1 /*
2 * Copyright (c) 2008, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
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24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.util.BitSet;
30 import java.util.List;
31 import java.util.ArrayList;
32 import java.util.Arrays;
33
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.CallerSensitive;
38 import sun.reflect.Reflection;
39 import sun.reflect.misc.ReflectUtil;
40 import sun.security.util.SecurityConstants;
41 import java.lang.invoke.LambdaForm.BasicType;
42 import static java.lang.invoke.LambdaForm.BasicType.*;
43 import static java.lang.invoke.MethodHandleStatics.*;
44 import static java.lang.invoke.MethodHandleNatives.Constants.*;
45 import java.util.concurrent.ConcurrentHashMap;
46
47 /**
48 * This class consists exclusively of static methods that operate on or return
49 * method handles. They fall into several categories:
50 * <ul>
51 * <li>Lookup methods which help create method handles for methods and fields.
52 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
53 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
54 * </ul>
55 *
56 * @author John Rose, JSR 292 EG
57 * @since 1.7
58 */
59 public class MethodHandles {
60
61 private MethodHandles() { } // do not instantiate
62
63 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
64 static { MethodHandleImpl.initStatics(); }
65 // See IMPL_LOOKUP below.
66
67 //// Method handle creation from ordinary methods.
68
69 /**
70 * Returns a {@link Lookup lookup object} with
71 * full capabilities to emulate all supported bytecode behaviors of the caller.
72 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
73 * Factory methods on the lookup object can create
74 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
75 * for any member that the caller has access to via bytecodes,
76 * including protected and private fields and methods.
77 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
78 * Do not store it in place where untrusted code can access it.
79 * <p>
80 * This method is caller sensitive, which means that it may return different
81 * values to different callers.
82 * <p>
83 * For any given caller class {@code C}, the lookup object returned by this call
84 * has equivalent capabilities to any lookup object
85 * supplied by the JVM to the bootstrap method of an
86 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
87 * executing in the same caller class {@code C}.
88 * @return a lookup object for the caller of this method, with private access
89 */
90 @CallerSensitive
91 public static Lookup lookup() {
92 return new Lookup(Reflection.getCallerClass());
93 }
94
95 /**
96 * Returns a {@link Lookup lookup object} which is trusted minimally.
97 * It can only be used to create method handles to
98 * publicly accessible fields and methods.
99 * <p>
100 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
101 * of this lookup object will be {@link java.lang.Object}.
102 *
103 * <p style="font-size:smaller;">
104 * <em>Discussion:</em>
105 * The lookup class can be changed to any other class {@code C} using an expression of the form
106 * {@link Lookup#in publicLookup().in(C.class)}.
107 * Since all classes have equal access to public names,
108 * such a change would confer no new access rights.
109 * A public lookup object is always subject to
110 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
111 * Also, it cannot access
112 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
113 * @return a lookup object which is trusted minimally
114 */
115 public static Lookup publicLookup() {
116 return Lookup.PUBLIC_LOOKUP;
117 }
118
119 /**
120 * Performs an unchecked "crack" of a
121 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
122 * The result is as if the user had obtained a lookup object capable enough
123 * to crack the target method handle, called
124 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
125 * on the target to obtain its symbolic reference, and then called
126 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
127 * to resolve the symbolic reference to a member.
128 * <p>
129 * If there is a security manager, its {@code checkPermission} method
130 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
131 * @param <T> the desired type of the result, either {@link Member} or a subtype
132 * @param target a direct method handle to crack into symbolic reference components
133 * @param expected a class object representing the desired result type {@code T}
134 * @return a reference to the method, constructor, or field object
135 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
136 * @exception NullPointerException if either argument is {@code null}
137 * @exception IllegalArgumentException if the target is not a direct method handle
138 * @exception ClassCastException if the member is not of the expected type
139 * @since 1.8
140 */
141 public static <T extends Member> T
142 reflectAs(Class<T> expected, MethodHandle target) {
143 SecurityManager smgr = System.getSecurityManager();
144 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
145 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
146 return lookup.revealDirect(target).reflectAs(expected, lookup);
147 }
148 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
149 static final private java.security.Permission ACCESS_PERMISSION =
150 new ReflectPermission("suppressAccessChecks");
151
152 /**
153 * A <em>lookup object</em> is a factory for creating method handles,
154 * when the creation requires access checking.
155 * Method handles do not perform
156 * access checks when they are called, but rather when they are created.
157 * Therefore, method handle access
158 * restrictions must be enforced when a method handle is created.
159 * The caller class against which those restrictions are enforced
160 * is known as the {@linkplain #lookupClass lookup class}.
161 * <p>
162 * A lookup class which needs to create method handles will call
163 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
164 * When the {@code Lookup} factory object is created, the identity of the lookup class is
165 * determined, and securely stored in the {@code Lookup} object.
166 * The lookup class (or its delegates) may then use factory methods
167 * on the {@code Lookup} object to create method handles for access-checked members.
168 * This includes all methods, constructors, and fields which are allowed to the lookup class,
169 * even private ones.
170 *
171 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
172 * The factory methods on a {@code Lookup} object correspond to all major
173 * use cases for methods, constructors, and fields.
174 * Each method handle created by a factory method is the functional
175 * equivalent of a particular <em>bytecode behavior</em>.
176 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
177 * Here is a summary of the correspondence between these factory methods and
178 * the behavior the resulting method handles:
179 * <table border=1 cellpadding=5 summary="lookup method behaviors">
180 * <tr>
181 * <th><a name="equiv"></a>lookup expression</th>
182 * <th>member</th>
183 * <th>bytecode behavior</th>
184 * </tr>
185 * <tr>
186 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
187 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
188 * </tr>
189 * <tr>
190 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
191 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
192 * </tr>
193 * <tr>
194 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
195 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
196 * </tr>
197 * <tr>
198 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
199 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
200 * </tr>
201 * <tr>
202 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
203 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
204 * </tr>
205 * <tr>
206 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
207 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
208 * </tr>
209 * <tr>
210 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
211 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
212 * </tr>
213 * <tr>
214 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
215 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
216 * </tr>
217 * <tr>
218 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
219 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
220 * </tr>
221 * <tr>
222 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
223 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
224 * </tr>
225 * <tr>
226 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
227 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
228 * </tr>
229 * <tr>
230 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
231 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
232 * </tr>
233 * <tr>
234 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
235 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
236 * </tr>
237 * </table>
238 *
239 * Here, the type {@code C} is the class or interface being searched for a member,
240 * documented as a parameter named {@code refc} in the lookup methods.
241 * The method type {@code MT} is composed from the return type {@code T}
242 * and the sequence of argument types {@code A*}.
243 * The constructor also has a sequence of argument types {@code A*} and
244 * is deemed to return the newly-created object of type {@code C}.
245 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
246 * The formal parameter {@code this} stands for the self-reference of type {@code C};
247 * if it is present, it is always the leading argument to the method handle invocation.
248 * (In the case of some {@code protected} members, {@code this} may be
249 * restricted in type to the lookup class; see below.)
250 * The name {@code arg} stands for all the other method handle arguments.
251 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
252 * stands for a null reference if the accessed method or field is static,
253 * and {@code this} otherwise.
254 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
255 * for reflective objects corresponding to the given members.
256 * <p>
257 * In cases where the given member is of variable arity (i.e., a method or constructor)
258 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
259 * In all other cases, the returned method handle will be of fixed arity.
260 * <p style="font-size:smaller;">
261 * <em>Discussion:</em>
262 * The equivalence between looked-up method handles and underlying
263 * class members and bytecode behaviors
264 * can break down in a few ways:
265 * <ul style="font-size:smaller;">
266 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
267 * the lookup can still succeed, even when there is no equivalent
268 * Java expression or bytecoded constant.
269 * <li>Likewise, if {@code T} or {@code MT}
270 * is not symbolically accessible from the lookup class's loader,
271 * the lookup can still succeed.
272 * For example, lookups for {@code MethodHandle.invokeExact} and
273 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
274 * <li>If there is a security manager installed, it can forbid the lookup
275 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
276 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
277 * constant is not subject to security manager checks.
278 * <li>If the looked-up method has a
279 * <a href="MethodHandle.html#maxarity">very large arity</a>,
280 * the method handle creation may fail, due to the method handle
281 * type having too many parameters.
282 * </ul>
283 *
284 * <h1><a name="access"></a>Access checking</h1>
285 * Access checks are applied in the factory methods of {@code Lookup},
286 * when a method handle is created.
287 * This is a key difference from the Core Reflection API, since
288 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
289 * performs access checking against every caller, on every call.
290 * <p>
291 * All access checks start from a {@code Lookup} object, which
292 * compares its recorded lookup class against all requests to
293 * create method handles.
294 * A single {@code Lookup} object can be used to create any number
295 * of access-checked method handles, all checked against a single
296 * lookup class.
297 * <p>
298 * A {@code Lookup} object can be shared with other trusted code,
299 * such as a metaobject protocol.
300 * A shared {@code Lookup} object delegates the capability
301 * to create method handles on private members of the lookup class.
302 * Even if privileged code uses the {@code Lookup} object,
303 * the access checking is confined to the privileges of the
304 * original lookup class.
305 * <p>
306 * A lookup can fail, because
307 * the containing class is not accessible to the lookup class, or
308 * because the desired class member is missing, or because the
309 * desired class member is not accessible to the lookup class, or
310 * because the lookup object is not trusted enough to access the member.
311 * In any of these cases, a {@code ReflectiveOperationException} will be
312 * thrown from the attempted lookup. The exact class will be one of
313 * the following:
314 * <ul>
315 * <li>NoSuchMethodException — if a method is requested but does not exist
316 * <li>NoSuchFieldException — if a field is requested but does not exist
317 * <li>IllegalAccessException — if the member exists but an access check fails
318 * </ul>
319 * <p>
320 * In general, the conditions under which a method handle may be
321 * looked up for a method {@code M} are no more restrictive than the conditions
322 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
323 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
324 * a method handle lookup will generally raise a corresponding
325 * checked exception, such as {@code NoSuchMethodException}.
326 * And the effect of invoking the method handle resulting from the lookup
327 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
328 * to executing the compiled, verified, and resolved call to {@code M}.
329 * The same point is true of fields and constructors.
330 * <p style="font-size:smaller;">
331 * <em>Discussion:</em>
332 * Access checks only apply to named and reflected methods,
333 * constructors, and fields.
334 * Other method handle creation methods, such as
335 * {@link MethodHandle#asType MethodHandle.asType},
336 * do not require any access checks, and are used
337 * independently of any {@code Lookup} object.
338 * <p>
339 * If the desired member is {@code protected}, the usual JVM rules apply,
340 * including the requirement that the lookup class must be either be in the
341 * same package as the desired member, or must inherit that member.
342 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
343 * In addition, if the desired member is a non-static field or method
344 * in a different package, the resulting method handle may only be applied
345 * to objects of the lookup class or one of its subclasses.
346 * This requirement is enforced by narrowing the type of the leading
347 * {@code this} parameter from {@code C}
348 * (which will necessarily be a superclass of the lookup class)
349 * to the lookup class itself.
350 * <p>
351 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
352 * that the receiver argument must match both the resolved method <em>and</em>
353 * the current class. Again, this requirement is enforced by narrowing the
354 * type of the leading parameter to the resulting method handle.
355 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
356 * <p>
357 * The JVM represents constructors and static initializer blocks as internal methods
358 * with special names ({@code "<init>"} and {@code "<clinit>"}).
359 * The internal syntax of invocation instructions allows them to refer to such internal
360 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
361 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
362 * <p>
363 * In some cases, access between nested classes is obtained by the Java compiler by creating
364 * an wrapper method to access a private method of another class
365 * in the same top-level declaration.
366 * For example, a nested class {@code C.D}
367 * can access private members within other related classes such as
368 * {@code C}, {@code C.D.E}, or {@code C.B},
369 * but the Java compiler may need to generate wrapper methods in
370 * those related classes. In such cases, a {@code Lookup} object on
371 * {@code C.E} would be unable to those private members.
372 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
373 * which can transform a lookup on {@code C.E} into one on any of those other
374 * classes, without special elevation of privilege.
375 * <p>
376 * The accesses permitted to a given lookup object may be limited,
377 * according to its set of {@link #lookupModes lookupModes},
378 * to a subset of members normally accessible to the lookup class.
379 * For example, the {@link MethodHandles#publicLookup publicLookup}
380 * method produces a lookup object which is only allowed to access
381 * public members in public classes.
382 * The caller sensitive method {@link MethodHandles#lookup lookup}
383 * produces a lookup object with full capabilities relative to
384 * its caller class, to emulate all supported bytecode behaviors.
385 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
386 * with fewer access modes than the original lookup object.
387 *
388 * <p style="font-size:smaller;">
389 * <a name="privacc"></a>
390 * <em>Discussion of private access:</em>
391 * We say that a lookup has <em>private access</em>
392 * if its {@linkplain #lookupModes lookup modes}
393 * include the possibility of accessing {@code private} members.
394 * As documented in the relevant methods elsewhere,
395 * only lookups with private access possess the following capabilities:
396 * <ul style="font-size:smaller;">
397 * <li>access private fields, methods, and constructors of the lookup class
398 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
399 * such as {@code Class.forName}
400 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
401 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
402 * for classes accessible to the lookup class
403 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
404 * within the same package member
405 * </ul>
406 * <p style="font-size:smaller;">
407 * Each of these permissions is a consequence of the fact that a lookup object
408 * with private access can be securely traced back to an originating class,
409 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
410 * can be reliably determined and emulated by method handles.
411 *
412 * <h1><a name="secmgr"></a>Security manager interactions</h1>
413 * Although bytecode instructions can only refer to classes in
414 * a related class loader, this API can search for methods in any
415 * class, as long as a reference to its {@code Class} object is
416 * available. Such cross-loader references are also possible with the
417 * Core Reflection API, and are impossible to bytecode instructions
418 * such as {@code invokestatic} or {@code getfield}.
419 * There is a {@linkplain java.lang.SecurityManager security manager API}
420 * to allow applications to check such cross-loader references.
421 * These checks apply to both the {@code MethodHandles.Lookup} API
422 * and the Core Reflection API
423 * (as found on {@link java.lang.Class Class}).
424 * <p>
425 * If a security manager is present, member lookups are subject to
426 * additional checks.
427 * From one to three calls are made to the security manager.
428 * Any of these calls can refuse access by throwing a
429 * {@link java.lang.SecurityException SecurityException}.
430 * Define {@code smgr} as the security manager,
431 * {@code lookc} as the lookup class of the current lookup object,
432 * {@code refc} as the containing class in which the member
433 * is being sought, and {@code defc} as the class in which the
434 * member is actually defined.
435 * The value {@code lookc} is defined as <em>not present</em>
436 * if the current lookup object does not have
437 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
438 * The calls are made according to the following rules:
439 * <ul>
440 * <li><b>Step 1:</b>
441 * If {@code lookc} is not present, or if its class loader is not
442 * the same as or an ancestor of the class loader of {@code refc},
443 * then {@link SecurityManager#checkPackageAccess
444 * smgr.checkPackageAccess(refcPkg)} is called,
445 * where {@code refcPkg} is the package of {@code refc}.
446 * <li><b>Step 2:</b>
447 * If the retrieved member is not public and
448 * {@code lookc} is not present, then
449 * {@link SecurityManager#checkPermission smgr.checkPermission}
450 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
451 * <li><b>Step 3:</b>
452 * If the retrieved member is not public,
453 * and if {@code lookc} is not present,
454 * and if {@code defc} and {@code refc} are different,
455 * then {@link SecurityManager#checkPackageAccess
456 * smgr.checkPackageAccess(defcPkg)} is called,
457 * where {@code defcPkg} is the package of {@code defc}.
458 * </ul>
459 * Security checks are performed after other access checks have passed.
460 * Therefore, the above rules presuppose a member that is public,
461 * or else that is being accessed from a lookup class that has
462 * rights to access the member.
463 *
464 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
465 * A small number of Java methods have a special property called caller sensitivity.
466 * A <em>caller-sensitive</em> method can behave differently depending on the
467 * identity of its immediate caller.
468 * <p>
469 * If a method handle for a caller-sensitive method is requested,
470 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
471 * but they take account of the lookup class in a special way.
472 * The resulting method handle behaves as if it were called
473 * from an instruction contained in the lookup class,
474 * so that the caller-sensitive method detects the lookup class.
475 * (By contrast, the invoker of the method handle is disregarded.)
476 * Thus, in the case of caller-sensitive methods,
477 * different lookup classes may give rise to
478 * differently behaving method handles.
479 * <p>
480 * In cases where the lookup object is
481 * {@link MethodHandles#publicLookup() publicLookup()},
482 * or some other lookup object without
483 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
484 * the lookup class is disregarded.
485 * In such cases, no caller-sensitive method handle can be created,
486 * access is forbidden, and the lookup fails with an
487 * {@code IllegalAccessException}.
488 * <p style="font-size:smaller;">
489 * <em>Discussion:</em>
490 * For example, the caller-sensitive method
491 * {@link java.lang.Class#forName(String) Class.forName(x)}
492 * can return varying classes or throw varying exceptions,
493 * depending on the class loader of the class that calls it.
494 * A public lookup of {@code Class.forName} will fail, because
495 * there is no reasonable way to determine its bytecode behavior.
496 * <p style="font-size:smaller;">
497 * If an application caches method handles for broad sharing,
498 * it should use {@code publicLookup()} to create them.
499 * If there is a lookup of {@code Class.forName}, it will fail,
500 * and the application must take appropriate action in that case.
501 * It may be that a later lookup, perhaps during the invocation of a
502 * bootstrap method, can incorporate the specific identity
503 * of the caller, making the method accessible.
504 * <p style="font-size:smaller;">
505 * The function {@code MethodHandles.lookup} is caller sensitive
506 * so that there can be a secure foundation for lookups.
507 * Nearly all other methods in the JSR 292 API rely on lookup
508 * objects to check access requests.
509 */
510 public static final
511 class Lookup {
512 /** The class on behalf of whom the lookup is being performed. */
513 private final Class<?> lookupClass;
514
515 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
516 private final int allowedModes;
517
518 /** A single-bit mask representing {@code public} access,
519 * which may contribute to the result of {@link #lookupModes lookupModes}.
520 * The value, {@code 0x01}, happens to be the same as the value of the
521 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
522 */
523 public static final int PUBLIC = Modifier.PUBLIC;
524
525 /** A single-bit mask representing {@code private} access,
526 * which may contribute to the result of {@link #lookupModes lookupModes}.
527 * The value, {@code 0x02}, happens to be the same as the value of the
528 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
529 */
530 public static final int PRIVATE = Modifier.PRIVATE;
531
532 /** A single-bit mask representing {@code protected} access,
533 * which may contribute to the result of {@link #lookupModes lookupModes}.
534 * The value, {@code 0x04}, happens to be the same as the value of the
535 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
536 */
537 public static final int PROTECTED = Modifier.PROTECTED;
538
539 /** A single-bit mask representing {@code package} access (default access),
540 * which may contribute to the result of {@link #lookupModes lookupModes}.
541 * The value is {@code 0x08}, which does not correspond meaningfully to
542 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
543 */
544 public static final int PACKAGE = Modifier.STATIC;
545
546 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
547 private static final int TRUSTED = -1;
548
549 private static int fixmods(int mods) {
550 mods &= (ALL_MODES - PACKAGE);
551 return (mods != 0) ? mods : PACKAGE;
552 }
553
554 /** Tells which class is performing the lookup. It is this class against
555 * which checks are performed for visibility and access permissions.
556 * <p>
557 * The class implies a maximum level of access permission,
558 * but the permissions may be additionally limited by the bitmask
559 * {@link #lookupModes lookupModes}, which controls whether non-public members
560 * can be accessed.
561 * @return the lookup class, on behalf of which this lookup object finds members
562 */
563 public Class<?> lookupClass() {
564 return lookupClass;
565 }
566
567 // This is just for calling out to MethodHandleImpl.
568 private Class<?> lookupClassOrNull() {
569 return (allowedModes == TRUSTED) ? null : lookupClass;
570 }
571
572 /** Tells which access-protection classes of members this lookup object can produce.
573 * The result is a bit-mask of the bits
574 * {@linkplain #PUBLIC PUBLIC (0x01)},
575 * {@linkplain #PRIVATE PRIVATE (0x02)},
576 * {@linkplain #PROTECTED PROTECTED (0x04)},
577 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
578 * <p>
579 * A freshly-created lookup object
580 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
581 * has all possible bits set, since the caller class can access all its own members.
582 * A lookup object on a new lookup class
583 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
584 * may have some mode bits set to zero.
585 * The purpose of this is to restrict access via the new lookup object,
586 * so that it can access only names which can be reached by the original
587 * lookup object, and also by the new lookup class.
588 * @return the lookup modes, which limit the kinds of access performed by this lookup object
589 */
590 public int lookupModes() {
591 return allowedModes & ALL_MODES;
592 }
593
594 /** Embody the current class (the lookupClass) as a lookup class
595 * for method handle creation.
596 * Must be called by from a method in this package,
597 * which in turn is called by a method not in this package.
598 */
599 Lookup(Class<?> lookupClass) {
600 this(lookupClass, ALL_MODES);
601 // make sure we haven't accidentally picked up a privileged class:
602 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
603 }
604
605 private Lookup(Class<?> lookupClass, int allowedModes) {
606 this.lookupClass = lookupClass;
607 this.allowedModes = allowedModes;
608 }
609
610 /**
611 * Creates a lookup on the specified new lookup class.
612 * The resulting object will report the specified
613 * class as its own {@link #lookupClass lookupClass}.
614 * <p>
615 * However, the resulting {@code Lookup} object is guaranteed
616 * to have no more access capabilities than the original.
617 * In particular, access capabilities can be lost as follows:<ul>
618 * <li>If the new lookup class differs from the old one,
619 * protected members will not be accessible by virtue of inheritance.
620 * (Protected members may continue to be accessible because of package sharing.)
621 * <li>If the new lookup class is in a different package
622 * than the old one, protected and default (package) members will not be accessible.
623 * <li>If the new lookup class is not within the same package member
624 * as the old one, private members will not be accessible.
625 * <li>If the new lookup class is not accessible to the old lookup class,
626 * then no members, not even public members, will be accessible.
627 * (In all other cases, public members will continue to be accessible.)
628 * </ul>
629 *
630 * @param requestedLookupClass the desired lookup class for the new lookup object
631 * @return a lookup object which reports the desired lookup class
632 * @throws NullPointerException if the argument is null
633 */
634 public Lookup in(Class<?> requestedLookupClass) {
635 requestedLookupClass.getClass(); // null check
636 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
637 return new Lookup(requestedLookupClass, ALL_MODES);
638 if (requestedLookupClass == this.lookupClass)
639 return this; // keep same capabilities
640 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
641 if ((newModes & PACKAGE) != 0
642 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
643 newModes &= ~(PACKAGE|PRIVATE);
644 }
645 // Allow nestmate lookups to be created without special privilege:
646 if ((newModes & PRIVATE) != 0
647 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
648 newModes &= ~PRIVATE;
649 }
650 if ((newModes & PUBLIC) != 0
651 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
652 // The requested class it not accessible from the lookup class.
653 // No permissions.
654 newModes = 0;
655 }
656 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
657 return new Lookup(requestedLookupClass, newModes);
658 }
659
660 // Make sure outer class is initialized first.
661 static { IMPL_NAMES.getClass(); }
662
663 /** Version of lookup which is trusted minimally.
664 * It can only be used to create method handles to
665 * publicly accessible members.
666 */
667 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
668
669 /** Package-private version of lookup which is trusted. */
670 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
671
672 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
673 String name = lookupClass.getName();
674 if (name.startsWith("java.lang.invoke."))
675 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
676
677 // For caller-sensitive MethodHandles.lookup()
678 // disallow lookup more restricted packages
679 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
680 if (name.startsWith("java.") ||
681 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
682 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
683 }
684 }
685 }
686
687 /**
688 * Displays the name of the class from which lookups are to be made.
689 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
690 * If there are restrictions on the access permitted to this lookup,
691 * this is indicated by adding a suffix to the class name, consisting
692 * of a slash and a keyword. The keyword represents the strongest
693 * allowed access, and is chosen as follows:
694 * <ul>
695 * <li>If no access is allowed, the suffix is "/noaccess".
696 * <li>If only public access is allowed, the suffix is "/public".
697 * <li>If only public and package access are allowed, the suffix is "/package".
698 * <li>If only public, package, and private access are allowed, the suffix is "/private".
699 * </ul>
700 * If none of the above cases apply, it is the case that full
701 * access (public, package, private, and protected) is allowed.
702 * In this case, no suffix is added.
703 * This is true only of an object obtained originally from
704 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
705 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
706 * always have restricted access, and will display a suffix.
707 * <p>
708 * (It may seem strange that protected access should be
709 * stronger than private access. Viewed independently from
710 * package access, protected access is the first to be lost,
711 * because it requires a direct subclass relationship between
712 * caller and callee.)
713 * @see #in
714 */
715 @Override
716 public String toString() {
717 String cname = lookupClass.getName();
718 switch (allowedModes) {
719 case 0: // no privileges
720 return cname + "/noaccess";
721 case PUBLIC:
722 return cname + "/public";
723 case PUBLIC|PACKAGE:
724 return cname + "/package";
725 case ALL_MODES & ~PROTECTED:
726 return cname + "/private";
727 case ALL_MODES:
728 return cname;
729 case TRUSTED:
730 return "/trusted"; // internal only; not exported
731 default: // Should not happen, but it's a bitfield...
732 cname = cname + "/" + Integer.toHexString(allowedModes);
733 assert(false) : cname;
734 return cname;
735 }
736 }
737
738 /**
739 * Produces a method handle for a static method.
740 * The type of the method handle will be that of the method.
741 * (Since static methods do not take receivers, there is no
742 * additional receiver argument inserted into the method handle type,
743 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
744 * The method and all its argument types must be accessible to the lookup object.
745 * <p>
746 * The returned method handle will have
747 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
748 * the method's variable arity modifier bit ({@code 0x0080}) is set.
749 * <p>
750 * If the returned method handle is invoked, the method's class will
751 * be initialized, if it has not already been initialized.
752 * <p><b>Example:</b>
753 * <blockquote><pre>{@code
754 import static java.lang.invoke.MethodHandles.*;
755 import static java.lang.invoke.MethodType.*;
756 ...
757 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
758 "asList", methodType(List.class, Object[].class));
759 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
760 * }</pre></blockquote>
761 * @param refc the class from which the method is accessed
762 * @param name the name of the method
763 * @param type the type of the method
764 * @return the desired method handle
765 * @throws NoSuchMethodException if the method does not exist
766 * @throws IllegalAccessException if access checking fails,
767 * or if the method is not {@code static},
768 * or if the method's variable arity modifier bit
769 * is set and {@code asVarargsCollector} fails
770 * @exception SecurityException if a security manager is present and it
771 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
772 * @throws NullPointerException if any argument is null
773 */
774 public
775 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
776 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
777 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
778 }
779
780 /**
781 * Produces a method handle for a virtual method.
782 * The type of the method handle will be that of the method,
783 * with the receiver type (usually {@code refc}) prepended.
784 * The method and all its argument types must be accessible to the lookup object.
785 * <p>
786 * When called, the handle will treat the first argument as a receiver
787 * and dispatch on the receiver's type to determine which method
788 * implementation to enter.
789 * (The dispatching action is identical with that performed by an
790 * {@code invokevirtual} or {@code invokeinterface} instruction.)
791 * <p>
792 * The first argument will be of type {@code refc} if the lookup
793 * class has full privileges to access the member. Otherwise
794 * the member must be {@code protected} and the first argument
795 * will be restricted in type to the lookup class.
796 * <p>
797 * The returned method handle will have
798 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
799 * the method's variable arity modifier bit ({@code 0x0080}) is set.
800 * <p>
801 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
802 * instructions and method handles produced by {@code findVirtual},
803 * if the class is {@code MethodHandle} and the name string is
804 * {@code invokeExact} or {@code invoke}, the resulting
805 * method handle is equivalent to one produced by
806 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
807 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
808 * with the same {@code type} argument.
809 *
810 * <b>Example:</b>
811 * <blockquote><pre>{@code
812 import static java.lang.invoke.MethodHandles.*;
813 import static java.lang.invoke.MethodType.*;
814 ...
815 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
816 "concat", methodType(String.class, String.class));
817 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
818 "hashCode", methodType(int.class));
819 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
820 "hashCode", methodType(int.class));
821 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
822 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
823 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
824 // interface method:
825 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
826 "subSequence", methodType(CharSequence.class, int.class, int.class));
827 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
828 // constructor "internal method" must be accessed differently:
829 MethodType MT_newString = methodType(void.class); //()V for new String()
830 try { assertEquals("impossible", lookup()
831 .findVirtual(String.class, "<init>", MT_newString));
832 } catch (NoSuchMethodException ex) { } // OK
833 MethodHandle MH_newString = publicLookup()
834 .findConstructor(String.class, MT_newString);
835 assertEquals("", (String) MH_newString.invokeExact());
836 * }</pre></blockquote>
837 *
838 * @param refc the class or interface from which the method is accessed
839 * @param name the name of the method
840 * @param type the type of the method, with the receiver argument omitted
841 * @return the desired method handle
842 * @throws NoSuchMethodException if the method does not exist
843 * @throws IllegalAccessException if access checking fails,
844 * or if the method is {@code static}
845 * or if the method's variable arity modifier bit
846 * is set and {@code asVarargsCollector} fails
847 * @exception SecurityException if a security manager is present and it
848 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
849 * @throws NullPointerException if any argument is null
850 */
851 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
852 if (refc == MethodHandle.class) {
853 MethodHandle mh = findVirtualForMH(name, type);
854 if (mh != null) return mh;
855 }
856 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
857 MemberName method = resolveOrFail(refKind, refc, name, type);
858 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
859 }
860 private MethodHandle findVirtualForMH(String name, MethodType type) {
861 // these names require special lookups because of the implicit MethodType argument
862 if ("invoke".equals(name))
863 return invoker(type);
864 if ("invokeExact".equals(name))
865 return exactInvoker(type);
866 if ("invokeBasic".equals(name))
867 return basicInvoker(type);
868 assert(!MemberName.isMethodHandleInvokeName(name));
869 return null;
870 }
871
872 /**
873 * Produces a method handle which creates an object and initializes it, using
874 * the constructor of the specified type.
875 * The parameter types of the method handle will be those of the constructor,
876 * while the return type will be a reference to the constructor's class.
877 * The constructor and all its argument types must be accessible to the lookup object.
878 * <p>
879 * The requested type must have a return type of {@code void}.
880 * (This is consistent with the JVM's treatment of constructor type descriptors.)
881 * <p>
882 * The returned method handle will have
883 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
884 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
885 * <p>
886 * If the returned method handle is invoked, the constructor's class will
887 * be initialized, if it has not already been initialized.
888 * <p><b>Example:</b>
889 * <blockquote><pre>{@code
890 import static java.lang.invoke.MethodHandles.*;
891 import static java.lang.invoke.MethodType.*;
892 ...
893 MethodHandle MH_newArrayList = publicLookup().findConstructor(
894 ArrayList.class, methodType(void.class, Collection.class));
895 Collection orig = Arrays.asList("x", "y");
896 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
897 assert(orig != copy);
898 assertEquals(orig, copy);
899 // a variable-arity constructor:
900 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
901 ProcessBuilder.class, methodType(void.class, String[].class));
902 ProcessBuilder pb = (ProcessBuilder)
903 MH_newProcessBuilder.invoke("x", "y", "z");
904 assertEquals("[x, y, z]", pb.command().toString());
905 * }</pre></blockquote>
906 * @param refc the class or interface from which the method is accessed
907 * @param type the type of the method, with the receiver argument omitted, and a void return type
908 * @return the desired method handle
909 * @throws NoSuchMethodException if the constructor does not exist
910 * @throws IllegalAccessException if access checking fails
911 * or if the method's variable arity modifier bit
912 * is set and {@code asVarargsCollector} fails
913 * @exception SecurityException if a security manager is present and it
914 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
915 * @throws NullPointerException if any argument is null
916 */
917 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
918 String name = "<init>";
919 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
920 return getDirectConstructor(refc, ctor);
921 }
922
923 /**
924 * Produces an early-bound method handle for a virtual method.
925 * It will bypass checks for overriding methods on the receiver,
926 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
927 * instruction from within the explicitly specified {@code specialCaller}.
928 * The type of the method handle will be that of the method,
929 * with a suitably restricted receiver type prepended.
930 * (The receiver type will be {@code specialCaller} or a subtype.)
931 * The method and all its argument types must be accessible
932 * to the lookup object.
933 * <p>
934 * Before method resolution,
935 * if the explicitly specified caller class is not identical with the
936 * lookup class, or if this lookup object does not have
937 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
938 * privileges, the access fails.
939 * <p>
940 * The returned method handle will have
941 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
942 * the method's variable arity modifier bit ({@code 0x0080}) is set.
943 * <p style="font-size:smaller;">
944 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
945 * even though the {@code invokespecial} instruction can refer to them
946 * in special circumstances. Use {@link #findConstructor findConstructor}
947 * to access instance initialization methods in a safe manner.)</em>
948 * <p><b>Example:</b>
949 * <blockquote><pre>{@code
950 import static java.lang.invoke.MethodHandles.*;
951 import static java.lang.invoke.MethodType.*;
952 ...
953 static class Listie extends ArrayList {
954 public String toString() { return "[wee Listie]"; }
955 static Lookup lookup() { return MethodHandles.lookup(); }
956 }
957 ...
958 // no access to constructor via invokeSpecial:
959 MethodHandle MH_newListie = Listie.lookup()
960 .findConstructor(Listie.class, methodType(void.class));
961 Listie l = (Listie) MH_newListie.invokeExact();
962 try { assertEquals("impossible", Listie.lookup().findSpecial(
963 Listie.class, "<init>", methodType(void.class), Listie.class));
964 } catch (NoSuchMethodException ex) { } // OK
965 // access to super and self methods via invokeSpecial:
966 MethodHandle MH_super = Listie.lookup().findSpecial(
967 ArrayList.class, "toString" , methodType(String.class), Listie.class);
968 MethodHandle MH_this = Listie.lookup().findSpecial(
969 Listie.class, "toString" , methodType(String.class), Listie.class);
970 MethodHandle MH_duper = Listie.lookup().findSpecial(
971 Object.class, "toString" , methodType(String.class), Listie.class);
972 assertEquals("[]", (String) MH_super.invokeExact(l));
973 assertEquals(""+l, (String) MH_this.invokeExact(l));
974 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
975 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
976 String.class, "toString", methodType(String.class), Listie.class));
977 } catch (IllegalAccessException ex) { } // OK
978 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
979 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
980 * }</pre></blockquote>
981 *
982 * @param refc the class or interface from which the method is accessed
983 * @param name the name of the method (which must not be "<init>")
984 * @param type the type of the method, with the receiver argument omitted
985 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
986 * @return the desired method handle
987 * @throws NoSuchMethodException if the method does not exist
988 * @throws IllegalAccessException if access checking fails
989 * or if the method's variable arity modifier bit
990 * is set and {@code asVarargsCollector} fails
991 * @exception SecurityException if a security manager is present and it
992 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
993 * @throws NullPointerException if any argument is null
994 */
995 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
996 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
997 checkSpecialCaller(specialCaller);
998 Lookup specialLookup = this.in(specialCaller);
999 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1000 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1001 }
1002
1003 /**
1004 * Produces a method handle giving read access to a non-static field.
1005 * The type of the method handle will have a return type of the field's
1006 * value type.
1007 * The method handle's single argument will be the instance containing
1008 * the field.
1009 * Access checking is performed immediately on behalf of the lookup class.
1010 * @param refc the class or interface from which the method is accessed
1011 * @param name the field's name
1012 * @param type the field's type
1013 * @return a method handle which can load values from the field
1014 * @throws NoSuchFieldException if the field does not exist
1015 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1016 * @exception SecurityException if a security manager is present and it
1017 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1018 * @throws NullPointerException if any argument is null
1019 */
1020 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1021 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1022 return getDirectField(REF_getField, refc, field);
1023 }
1024
1025 /**
1026 * Produces a method handle giving write access to a non-static field.
1027 * The type of the method handle will have a void return type.
1028 * The method handle will take two arguments, the instance containing
1029 * the field, and the value to be stored.
1030 * The second argument will be of the field's value type.
1031 * Access checking is performed immediately on behalf of the lookup class.
1032 * @param refc the class or interface from which the method is accessed
1033 * @param name the field's name
1034 * @param type the field's type
1035 * @return a method handle which can store values into the field
1036 * @throws NoSuchFieldException if the field does not exist
1037 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1038 * @exception SecurityException if a security manager is present and it
1039 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1040 * @throws NullPointerException if any argument is null
1041 */
1042 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1043 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1044 return getDirectField(REF_putField, refc, field);
1045 }
1046
1047 /**
1048 * Produces a method handle giving read access to a static field.
1049 * The type of the method handle will have a return type of the field's
1050 * value type.
1051 * The method handle will take no arguments.
1052 * Access checking is performed immediately on behalf of the lookup class.
1053 * <p>
1054 * If the returned method handle is invoked, the field's class will
1055 * be initialized, if it has not already been initialized.
1056 * @param refc the class or interface from which the method is accessed
1057 * @param name the field's name
1058 * @param type the field's type
1059 * @return a method handle which can load values from the field
1060 * @throws NoSuchFieldException if the field does not exist
1061 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1062 * @exception SecurityException if a security manager is present and it
1063 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1064 * @throws NullPointerException if any argument is null
1065 */
1066 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1067 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1068 return getDirectField(REF_getStatic, refc, field);
1069 }
1070
1071 /**
1072 * Produces a method handle giving write access to a static field.
1073 * The type of the method handle will have a void return type.
1074 * The method handle will take a single
1075 * argument, of the field's value type, the value to be stored.
1076 * Access checking is performed immediately on behalf of the lookup class.
1077 * <p>
1078 * If the returned method handle is invoked, the field's class will
1079 * be initialized, if it has not already been initialized.
1080 * @param refc the class or interface from which the method is accessed
1081 * @param name the field's name
1082 * @param type the field's type
1083 * @return a method handle which can store values into the field
1084 * @throws NoSuchFieldException if the field does not exist
1085 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1086 * @exception SecurityException if a security manager is present and it
1087 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1088 * @throws NullPointerException if any argument is null
1089 */
1090 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1091 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1092 return getDirectField(REF_putStatic, refc, field);
1093 }
1094
1095 /**
1096 * Produces an early-bound method handle for a non-static method.
1097 * The receiver must have a supertype {@code defc} in which a method
1098 * of the given name and type is accessible to the lookup class.
1099 * The method and all its argument types must be accessible to the lookup object.
1100 * The type of the method handle will be that of the method,
1101 * without any insertion of an additional receiver parameter.
1102 * The given receiver will be bound into the method handle,
1103 * so that every call to the method handle will invoke the
1104 * requested method on the given receiver.
1105 * <p>
1106 * The returned method handle will have
1107 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1108 * the method's variable arity modifier bit ({@code 0x0080}) is set
1109 * <em>and</em> the trailing array argument is not the only argument.
1110 * (If the trailing array argument is the only argument,
1111 * the given receiver value will be bound to it.)
1112 * <p>
1113 * This is equivalent to the following code:
1114 * <blockquote><pre>{@code
1115 import static java.lang.invoke.MethodHandles.*;
1116 import static java.lang.invoke.MethodType.*;
1117 ...
1118 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1119 MethodHandle mh1 = mh0.bindTo(receiver);
1120 MethodType mt1 = mh1.type();
1121 if (mh0.isVarargsCollector())
1122 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1123 return mh1;
1124 * }</pre></blockquote>
1125 * where {@code defc} is either {@code receiver.getClass()} or a super
1126 * type of that class, in which the requested method is accessible
1127 * to the lookup class.
1128 * (Note that {@code bindTo} does not preserve variable arity.)
1129 * @param receiver the object from which the method is accessed
1130 * @param name the name of the method
1131 * @param type the type of the method, with the receiver argument omitted
1132 * @return the desired method handle
1133 * @throws NoSuchMethodException if the method does not exist
1134 * @throws IllegalAccessException if access checking fails
1135 * or if the method's variable arity modifier bit
1136 * is set and {@code asVarargsCollector} fails
1137 * @exception SecurityException if a security manager is present and it
1138 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1139 * @throws NullPointerException if any argument is null
1140 * @see MethodHandle#bindTo
1141 * @see #findVirtual
1142 */
1143 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1144 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1145 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1146 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1147 return mh.bindArgumentL(0, receiver).setVarargs(method);
1148 }
1149
1150 /**
1151 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1152 * to <i>m</i>, if the lookup class has permission.
1153 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1154 * If <i>m</i> is virtual, overriding is respected on every call.
1155 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1156 * The type of the method handle will be that of the method,
1157 * with the receiver type prepended (but only if it is non-static).
1158 * If the method's {@code accessible} flag is not set,
1159 * access checking is performed immediately on behalf of the lookup class.
1160 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1161 * <p>
1162 * The returned method handle will have
1163 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1164 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1165 * <p>
1166 * If <i>m</i> is static, and
1167 * if the returned method handle is invoked, the method's class will
1168 * be initialized, if it has not already been initialized.
1169 * @param m the reflected method
1170 * @return a method handle which can invoke the reflected method
1171 * @throws IllegalAccessException if access checking fails
1172 * or if the method's variable arity modifier bit
1173 * is set and {@code asVarargsCollector} fails
1174 * @throws NullPointerException if the argument is null
1175 */
1176 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1177 if (m.getDeclaringClass() == MethodHandle.class) {
1178 MethodHandle mh = unreflectForMH(m);
1179 if (mh != null) return mh;
1180 }
1181 MemberName method = new MemberName(m);
1182 byte refKind = method.getReferenceKind();
1183 if (refKind == REF_invokeSpecial)
1184 refKind = REF_invokeVirtual;
1185 assert(method.isMethod());
1186 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1187 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1188 }
1189 private MethodHandle unreflectForMH(Method m) {
1190 // these names require special lookups because they throw UnsupportedOperationException
1191 if (MemberName.isMethodHandleInvokeName(m.getName()))
1192 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1193 return null;
1194 }
1195
1196 /**
1197 * Produces a method handle for a reflected method.
1198 * It will bypass checks for overriding methods on the receiver,
1199 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1200 * instruction from within the explicitly specified {@code specialCaller}.
1201 * The type of the method handle will be that of the method,
1202 * with a suitably restricted receiver type prepended.
1203 * (The receiver type will be {@code specialCaller} or a subtype.)
1204 * If the method's {@code accessible} flag is not set,
1205 * access checking is performed immediately on behalf of the lookup class,
1206 * as if {@code invokespecial} instruction were being linked.
1207 * <p>
1208 * Before method resolution,
1209 * if the explicitly specified caller class is not identical with the
1210 * lookup class, or if this lookup object does not have
1211 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1212 * privileges, the access fails.
1213 * <p>
1214 * The returned method handle will have
1215 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1216 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1217 * @param m the reflected method
1218 * @param specialCaller the class nominally calling the method
1219 * @return a method handle which can invoke the reflected method
1220 * @throws IllegalAccessException if access checking fails
1221 * or if the method's variable arity modifier bit
1222 * is set and {@code asVarargsCollector} fails
1223 * @throws NullPointerException if any argument is null
1224 */
1225 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1226 checkSpecialCaller(specialCaller);
1227 Lookup specialLookup = this.in(specialCaller);
1228 MemberName method = new MemberName(m, true);
1229 assert(method.isMethod());
1230 // ignore m.isAccessible: this is a new kind of access
1231 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1232 }
1233
1234 /**
1235 * Produces a method handle for a reflected constructor.
1236 * The type of the method handle will be that of the constructor,
1237 * with the return type changed to the declaring class.
1238 * The method handle will perform a {@code newInstance} operation,
1239 * creating a new instance of the constructor's class on the
1240 * arguments passed to the method handle.
1241 * <p>
1242 * If the constructor's {@code accessible} flag is not set,
1243 * access checking is performed immediately on behalf of the lookup class.
1244 * <p>
1245 * The returned method handle will have
1246 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1247 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1248 * <p>
1249 * If the returned method handle is invoked, the constructor's class will
1250 * be initialized, if it has not already been initialized.
1251 * @param c the reflected constructor
1252 * @return a method handle which can invoke the reflected constructor
1253 * @throws IllegalAccessException if access checking fails
1254 * or if the method's variable arity modifier bit
1255 * is set and {@code asVarargsCollector} fails
1256 * @throws NullPointerException if the argument is null
1257 */
1258 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1259 MemberName ctor = new MemberName(c);
1260 assert(ctor.isConstructor());
1261 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1262 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1263 }
1264
1265 /**
1266 * Produces a method handle giving read access to a reflected field.
1267 * The type of the method handle will have a return type of the field's
1268 * value type.
1269 * If the field is static, the method handle will take no arguments.
1270 * Otherwise, its single argument will be the instance containing
1271 * the field.
1272 * If the field's {@code accessible} flag is not set,
1273 * access checking is performed immediately on behalf of the lookup class.
1274 * <p>
1275 * If the field is static, and
1276 * if the returned method handle is invoked, the field's class will
1277 * be initialized, if it has not already been initialized.
1278 * @param f the reflected field
1279 * @return a method handle which can load values from the reflected field
1280 * @throws IllegalAccessException if access checking fails
1281 * @throws NullPointerException if the argument is null
1282 */
1283 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1284 return unreflectField(f, false);
1285 }
1286 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1287 MemberName field = new MemberName(f, isSetter);
1288 assert(isSetter
1289 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1290 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1291 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1292 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1293 }
1294
1295 /**
1296 * Produces a method handle giving write access to a reflected field.
1297 * The type of the method handle will have a void return type.
1298 * If the field is static, the method handle will take a single
1299 * argument, of the field's value type, the value to be stored.
1300 * Otherwise, the two arguments will be the instance containing
1301 * the field, and the value to be stored.
1302 * If the field's {@code accessible} flag is not set,
1303 * access checking is performed immediately on behalf of the lookup class.
1304 * <p>
1305 * If the field is static, and
1306 * if the returned method handle is invoked, the field's class will
1307 * be initialized, if it has not already been initialized.
1308 * @param f the reflected field
1309 * @return a method handle which can store values into the reflected field
1310 * @throws IllegalAccessException if access checking fails
1311 * @throws NullPointerException if the argument is null
1312 */
1313 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1314 return unreflectField(f, true);
1315 }
1316
1317 /**
1318 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1319 * created by this lookup object or a similar one.
1320 * Security and access checks are performed to ensure that this lookup object
1321 * is capable of reproducing the target method handle.
1322 * This means that the cracking may fail if target is a direct method handle
1323 * but was created by an unrelated lookup object.
1324 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1325 * and was created by a lookup object for a different class.
1326 * @param target a direct method handle to crack into symbolic reference components
1327 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1328 * @exception SecurityException if a security manager is present and it
1329 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1330 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1331 * @exception NullPointerException if the target is {@code null}
1332 * @see MethodHandleInfo
1333 * @since 1.8
1334 */
1335 public MethodHandleInfo revealDirect(MethodHandle target) {
1336 MemberName member = target.internalMemberName();
1337 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1338 throw newIllegalArgumentException("not a direct method handle");
1339 Class<?> defc = member.getDeclaringClass();
1340 byte refKind = member.getReferenceKind();
1341 assert(MethodHandleNatives.refKindIsValid(refKind));
1342 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1343 // Devirtualized method invocation is usually formally virtual.
1344 // To avoid creating extra MemberName objects for this common case,
1345 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1346 refKind = REF_invokeVirtual;
1347 if (refKind == REF_invokeVirtual && defc.isInterface())
1348 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1349 refKind = REF_invokeInterface;
1350 // Check SM permissions and member access before cracking.
1351 try {
1352 checkAccess(refKind, defc, member);
1353 checkSecurityManager(defc, member);
1354 } catch (IllegalAccessException ex) {
1355 throw new IllegalArgumentException(ex);
1356 }
1357 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1358 Class<?> callerClass = target.internalCallerClass();
1359 if (!hasPrivateAccess() || callerClass != lookupClass())
1360 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1361 }
1362 // Produce the handle to the results.
1363 return new InfoFromMemberName(this, member, refKind);
1364 }
1365
1366 /// Helper methods, all package-private.
1367
1368 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1369 checkSymbolicClass(refc); // do this before attempting to resolve
1370 name.getClass(); // NPE
1371 type.getClass(); // NPE
1372 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1373 NoSuchFieldException.class);
1374 }
1375
1376 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1377 checkSymbolicClass(refc); // do this before attempting to resolve
1378 name.getClass(); // NPE
1379 type.getClass(); // NPE
1380 checkMethodName(refKind, name); // NPE check on name
1381 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1382 NoSuchMethodException.class);
1383 }
1384
1385 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1386 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1387 member.getName().getClass(); // NPE
1388 member.getType().getClass(); // NPE
1389 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1390 ReflectiveOperationException.class);
1391 }
1392
1393 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1394 refc.getClass(); // NPE
1395 Class<?> caller = lookupClassOrNull();
1396 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1397 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1398 }
1399
1400 /** Check name for an illegal leading "<" character. */
1401 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1402 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1403 throw new NoSuchMethodException("illegal method name: "+name);
1404 }
1405
1406
1407 /**
1408 * Find my trustable caller class if m is a caller sensitive method.
1409 * If this lookup object has private access, then the caller class is the lookupClass.
1410 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1411 */
1412 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1413 Class<?> callerClass = null;
1414 if (MethodHandleNatives.isCallerSensitive(m)) {
1415 // Only lookups with private access are allowed to resolve caller-sensitive methods
1416 if (hasPrivateAccess()) {
1417 callerClass = lookupClass;
1418 } else {
1419 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1420 }
1421 }
1422 return callerClass;
1423 }
1424
1425 private boolean hasPrivateAccess() {
1426 return (allowedModes & PRIVATE) != 0;
1427 }
1428
1429 /**
1430 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1431 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1432 * If this lookup object has private access, then the caller class is the lookupClass.
1433 */
1434 void checkSecurityManager(Class<?> refc, MemberName m) {
1435 SecurityManager smgr = System.getSecurityManager();
1436 if (smgr == null) return;
1437 if (allowedModes == TRUSTED) return;
1438
1439 // Step 1:
1440 boolean fullPowerLookup = hasPrivateAccess();
1441 if (!fullPowerLookup ||
1442 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1443 ReflectUtil.checkPackageAccess(refc);
1444 }
1445
1446 // Step 2:
1447 if (m.isPublic()) return;
1448 if (!fullPowerLookup) {
1449 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1450 }
1451
1452 // Step 3:
1453 Class<?> defc = m.getDeclaringClass();
1454 if (!fullPowerLookup && defc != refc) {
1455 ReflectUtil.checkPackageAccess(defc);
1456 }
1457 }
1458
1459 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1460 boolean wantStatic = (refKind == REF_invokeStatic);
1461 String message;
1462 if (m.isConstructor())
1463 message = "expected a method, not a constructor";
1464 else if (!m.isMethod())
1465 message = "expected a method";
1466 else if (wantStatic != m.isStatic())
1467 message = wantStatic ? "expected a static method" : "expected a non-static method";
1468 else
1469 { checkAccess(refKind, refc, m); return; }
1470 throw m.makeAccessException(message, this);
1471 }
1472
1473 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1474 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1475 String message;
1476 if (wantStatic != m.isStatic())
1477 message = wantStatic ? "expected a static field" : "expected a non-static field";
1478 else
1479 { checkAccess(refKind, refc, m); return; }
1480 throw m.makeAccessException(message, this);
1481 }
1482
1483 /** Check public/protected/private bits on the symbolic reference class and its member. */
1484 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1485 assert(m.referenceKindIsConsistentWith(refKind) &&
1486 MethodHandleNatives.refKindIsValid(refKind) &&
1487 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1488 int allowedModes = this.allowedModes;
1489 if (allowedModes == TRUSTED) return;
1490 int mods = m.getModifiers();
1491 if (Modifier.isProtected(mods) &&
1492 refKind == REF_invokeVirtual &&
1493 m.getDeclaringClass() == Object.class &&
1494 m.getName().equals("clone") &&
1495 refc.isArray()) {
1496 // The JVM does this hack also.
1497 // (See ClassVerifier::verify_invoke_instructions
1498 // and LinkResolver::check_method_accessability.)
1499 // Because the JVM does not allow separate methods on array types,
1500 // there is no separate method for int[].clone.
1501 // All arrays simply inherit Object.clone.
1502 // But for access checking logic, we make Object.clone
1503 // (normally protected) appear to be public.
1504 // Later on, when the DirectMethodHandle is created,
1505 // its leading argument will be restricted to the
1506 // requested array type.
1507 // N.B. The return type is not adjusted, because
1508 // that is *not* the bytecode behavior.
1509 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1510 }
1511 if (Modifier.isFinal(mods) &&
1512 MethodHandleNatives.refKindIsSetter(refKind))
1513 throw m.makeAccessException("unexpected set of a final field", this);
1514 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1515 return; // common case
1516 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1517 if ((requestedModes & allowedModes) != 0) {
1518 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1519 mods, lookupClass(), allowedModes))
1520 return;
1521 } else {
1522 // Protected members can also be checked as if they were package-private.
1523 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1524 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1525 return;
1526 }
1527 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1528 }
1529
1530 String accessFailedMessage(Class<?> refc, MemberName m) {
1531 Class<?> defc = m.getDeclaringClass();
1532 int mods = m.getModifiers();
1533 // check the class first:
1534 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1535 (defc == refc ||
1536 Modifier.isPublic(refc.getModifiers())));
1537 if (!classOK && (allowedModes & PACKAGE) != 0) {
1538 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1539 (defc == refc ||
1540 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1541 }
1542 if (!classOK)
1543 return "class is not public";
1544 if (Modifier.isPublic(mods))
1545 return "access to public member failed"; // (how?)
1546 if (Modifier.isPrivate(mods))
1547 return "member is private";
1548 if (Modifier.isProtected(mods))
1549 return "member is protected";
1550 return "member is private to package";
1551 }
1552
1553 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1554
1555 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1556 int allowedModes = this.allowedModes;
1557 if (allowedModes == TRUSTED) return;
1558 if (!hasPrivateAccess()
1559 || (specialCaller != lookupClass()
1560 && !(ALLOW_NESTMATE_ACCESS &&
1561 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1562 throw new MemberName(specialCaller).
1563 makeAccessException("no private access for invokespecial", this);
1564 }
1565
1566 private boolean restrictProtectedReceiver(MemberName method) {
1567 // The accessing class only has the right to use a protected member
1568 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1569 if (!method.isProtected() || method.isStatic()
1570 || allowedModes == TRUSTED
1571 || method.getDeclaringClass() == lookupClass()
1572 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1573 || (ALLOW_NESTMATE_ACCESS &&
1574 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1575 return false;
1576 return true;
1577 }
1578 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1579 assert(!method.isStatic());
1580 // receiver type of mh is too wide; narrow to caller
1581 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1582 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1583 }
1584 MethodType rawType = mh.type();
1585 if (rawType.parameterType(0) == caller) return mh;
1586 MethodType narrowType = rawType.changeParameterType(0, caller);
1587 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1588 assert(mh.viewAsTypeChecks(narrowType, true));
1589 assert(mh instanceof DirectMethodHandle); // DirectMethodHandle.copyWith
1590 return mh.copyWith(narrowType, mh.form);
1591 }
1592
1593 /** Check access and get the requested method. */
1594 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1595 final boolean doRestrict = true;
1596 final boolean checkSecurity = true;
1597 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1598 }
1599 /** Check access and get the requested method, eliding receiver narrowing rules. */
1600 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1601 final boolean doRestrict = false;
1602 final boolean checkSecurity = true;
1603 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1604 }
1605 /** Check access and get the requested method, eliding security manager checks. */
1606 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1607 final boolean doRestrict = true;
1608 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1609 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1610 }
1611 /** Common code for all methods; do not call directly except from immediately above. */
1612 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1613 boolean checkSecurity,
1614 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1615 checkMethod(refKind, refc, method);
1616 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1617 if (checkSecurity)
1618 checkSecurityManager(refc, method);
1619 assert(!method.isMethodHandleInvoke());
1620
1621 if (refKind == REF_invokeSpecial &&
1622 refc != lookupClass() &&
1623 !refc.isInterface() &&
1624 refc != lookupClass().getSuperclass() &&
1625 refc.isAssignableFrom(lookupClass())) {
1626 assert(!method.getName().equals("<init>")); // not this code path
1627 // Per JVMS 6.5, desc. of invokespecial instruction:
1628 // If the method is in a superclass of the LC,
1629 // and if our original search was above LC.super,
1630 // repeat the search (symbolic lookup) from LC.super
1631 // and continue with the direct superclass of that class,
1632 // and so forth, until a match is found or no further superclasses exist.
1633 // FIXME: MemberName.resolve should handle this instead.
1634 Class<?> refcAsSuper = lookupClass();
1635 MemberName m2;
1636 do {
1637 refcAsSuper = refcAsSuper.getSuperclass();
1638 m2 = new MemberName(refcAsSuper,
1639 method.getName(),
1640 method.getMethodType(),
1641 REF_invokeSpecial);
1642 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1643 } while (m2 == null && // no method is found yet
1644 refc != refcAsSuper); // search up to refc
1645 if (m2 == null) throw new InternalError(method.toString());
1646 method = m2;
1647 refc = refcAsSuper;
1648 // redo basic checks
1649 checkMethod(refKind, refc, method);
1650 }
1651
1652 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1653 mh = maybeBindCaller(method, mh, callerClass);
1654 mh = mh.setVarargs(method);
1655 // Optionally narrow the receiver argument to refc using restrictReceiver.
1656 if (doRestrict &&
1657 (refKind == REF_invokeSpecial ||
1658 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1659 restrictProtectedReceiver(method))))
1660 mh = restrictReceiver(method, mh, lookupClass());
1661 return mh;
1662 }
1663 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1664 Class<?> callerClass)
1665 throws IllegalAccessException {
1666 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1667 return mh;
1668 Class<?> hostClass = lookupClass;
1669 if (!hasPrivateAccess()) // caller must have private access
1670 hostClass = callerClass; // callerClass came from a security manager style stack walk
1671 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1672 // Note: caller will apply varargs after this step happens.
1673 return cbmh;
1674 }
1675 /** Check access and get the requested field. */
1676 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1677 final boolean checkSecurity = true;
1678 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1679 }
1680 /** Check access and get the requested field, eliding security manager checks. */
1681 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1682 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1683 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1684 }
1685 /** Common code for all fields; do not call directly except from immediately above. */
1686 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1687 boolean checkSecurity) throws IllegalAccessException {
1688 checkField(refKind, refc, field);
1689 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1690 if (checkSecurity)
1691 checkSecurityManager(refc, field);
1692 MethodHandle mh = DirectMethodHandle.make(refc, field);
1693 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1694 restrictProtectedReceiver(field));
1695 if (doRestrict)
1696 mh = restrictReceiver(field, mh, lookupClass());
1697 return mh;
1698 }
1699 /** Check access and get the requested constructor. */
1700 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1701 final boolean checkSecurity = true;
1702 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1703 }
1704 /** Check access and get the requested constructor, eliding security manager checks. */
1705 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1706 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1707 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1708 }
1709 /** Common code for all constructors; do not call directly except from immediately above. */
1710 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1711 boolean checkSecurity) throws IllegalAccessException {
1712 assert(ctor.isConstructor());
1713 checkAccess(REF_newInvokeSpecial, refc, ctor);
1714 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1715 if (checkSecurity)
1716 checkSecurityManager(refc, ctor);
1717 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1718 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1719 }
1720
1721 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1722 */
1723 /*non-public*/
1724 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1725 if (!(type instanceof Class || type instanceof MethodType))
1726 throw new InternalError("unresolved MemberName");
1727 MemberName member = new MemberName(refKind, defc, name, type);
1728 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1729 if (mh != null) {
1730 checkSymbolicClass(defc);
1731 return mh;
1732 }
1733 // Treat MethodHandle.invoke and invokeExact specially.
1734 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1735 mh = findVirtualForMH(member.getName(), member.getMethodType());
1736 if (mh != null) {
1737 return mh;
1738 }
1739 }
1740 MemberName resolved = resolveOrFail(refKind, member);
1741 mh = getDirectMethodForConstant(refKind, defc, resolved);
1742 if (mh instanceof DirectMethodHandle
1743 && canBeCached(refKind, defc, resolved)) {
1744 MemberName key = mh.internalMemberName();
1745 if (key != null) {
1746 key = key.asNormalOriginal();
1747 }
1748 if (member.equals(key)) { // better safe than sorry
1749 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1750 }
1751 }
1752 return mh;
1753 }
1754 private
1755 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1756 if (refKind == REF_invokeSpecial) {
1757 return false;
1758 }
1759 if (!Modifier.isPublic(defc.getModifiers()) ||
1760 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1761 !member.isPublic() ||
1762 member.isCallerSensitive()) {
1763 return false;
1764 }
1765 ClassLoader loader = defc.getClassLoader();
1766 if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1767 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1768 boolean found = false;
1769 while (sysl != null) {
1770 if (loader == sysl) { found = true; break; }
1771 sysl = sysl.getParent();
1772 }
1773 if (!found) {
1774 return false;
1775 }
1776 }
1777 try {
1778 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1779 new MemberName(refKind, defc, member.getName(), member.getType()));
1780 checkSecurityManager(defc, resolved2);
1781 } catch (ReflectiveOperationException | SecurityException ex) {
1782 return false;
1783 }
1784 return true;
1785 }
1786 private
1787 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1788 throws ReflectiveOperationException {
1789 if (MethodHandleNatives.refKindIsField(refKind)) {
1790 return getDirectFieldNoSecurityManager(refKind, defc, member);
1791 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1792 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1793 } else if (refKind == REF_newInvokeSpecial) {
1794 return getDirectConstructorNoSecurityManager(defc, member);
1795 }
1796 // oops
1797 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1798 }
1799
1800 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1801 }
1802
1803 /**
1804 * Produces a method handle giving read access to elements of an array.
1805 * The type of the method handle will have a return type of the array's
1806 * element type. Its first argument will be the array type,
1807 * and the second will be {@code int}.
1808 * @param arrayClass an array type
1809 * @return a method handle which can load values from the given array type
1810 * @throws NullPointerException if the argument is null
1811 * @throws IllegalArgumentException if arrayClass is not an array type
1812 */
1813 public static
1814 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1815 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1816 }
1817
1818 /**
1819 * Produces a method handle giving write access to elements of an array.
1820 * The type of the method handle will have a void return type.
1821 * Its last argument will be the array's element type.
1822 * The first and second arguments will be the array type and int.
1823 * @param arrayClass the class of an array
1824 * @return a method handle which can store values into the array type
1825 * @throws NullPointerException if the argument is null
1826 * @throws IllegalArgumentException if arrayClass is not an array type
1827 */
1828 public static
1829 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1830 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1831 }
1832
1833 /// method handle invocation (reflective style)
1834
1835 /**
1836 * Produces a method handle which will invoke any method handle of the
1837 * given {@code type}, with a given number of trailing arguments replaced by
1838 * a single trailing {@code Object[]} array.
1839 * The resulting invoker will be a method handle with the following
1840 * arguments:
1841 * <ul>
1842 * <li>a single {@code MethodHandle} target
1843 * <li>zero or more leading values (counted by {@code leadingArgCount})
1844 * <li>an {@code Object[]} array containing trailing arguments
1845 * </ul>
1846 * <p>
1847 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1848 * the indicated {@code type}.
1849 * That is, if the target is exactly of the given {@code type}, it will behave
1850 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1851 * is used to convert the target to the required {@code type}.
1852 * <p>
1853 * The type of the returned invoker will not be the given {@code type}, but rather
1854 * will have all parameters except the first {@code leadingArgCount}
1855 * replaced by a single array of type {@code Object[]}, which will be
1856 * the final parameter.
1857 * <p>
1858 * Before invoking its target, the invoker will spread the final array, apply
1859 * reference casts as necessary, and unbox and widen primitive arguments.
1860 * If, when the invoker is called, the supplied array argument does
1861 * not have the correct number of elements, the invoker will throw
1862 * an {@link IllegalArgumentException} instead of invoking the target.
1863 * <p>
1864 * This method is equivalent to the following code (though it may be more efficient):
1865 * <blockquote><pre>{@code
1866 MethodHandle invoker = MethodHandles.invoker(type);
1867 int spreadArgCount = type.parameterCount() - leadingArgCount;
1868 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1869 return invoker;
1870 * }</pre></blockquote>
1871 * This method throws no reflective or security exceptions.
1872 * @param type the desired target type
1873 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1874 * @return a method handle suitable for invoking any method handle of the given type
1875 * @throws NullPointerException if {@code type} is null
1876 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1877 * the range from 0 to {@code type.parameterCount()} inclusive,
1878 * or if the resulting method handle's type would have
1879 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1880 */
1881 static public
1882 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1883 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1884 throw newIllegalArgumentException("bad argument count", leadingArgCount);
1885 return type.invokers().spreadInvoker(leadingArgCount);
1886 }
1887
1888 /**
1889 * Produces a special <em>invoker method handle</em> which can be used to
1890 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1891 * The resulting invoker will have a type which is
1892 * exactly equal to the desired type, except that it will accept
1893 * an additional leading argument of type {@code MethodHandle}.
1894 * <p>
1895 * This method is equivalent to the following code (though it may be more efficient):
1896 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1897 *
1898 * <p style="font-size:smaller;">
1899 * <em>Discussion:</em>
1900 * Invoker method handles can be useful when working with variable method handles
1901 * of unknown types.
1902 * For example, to emulate an {@code invokeExact} call to a variable method
1903 * handle {@code M}, extract its type {@code T},
1904 * look up the invoker method {@code X} for {@code T},
1905 * and call the invoker method, as {@code X.invoke(T, A...)}.
1906 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1907 * is unknown.)
1908 * If spreading, collecting, or other argument transformations are required,
1909 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1910 * method handle values, as long as they are compatible with the type of {@code X}.
1911 * <p style="font-size:smaller;">
1912 * <em>(Note: The invoker method is not available via the Core Reflection API.
1913 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1914 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1915 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1916 * <p>
1917 * This method throws no reflective or security exceptions.
1918 * @param type the desired target type
1919 * @return a method handle suitable for invoking any method handle of the given type
1920 * @throws IllegalArgumentException if the resulting method handle's type would have
1921 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1922 */
1923 static public
1924 MethodHandle exactInvoker(MethodType type) {
1925 return type.invokers().exactInvoker();
1926 }
1927
1928 /**
1929 * Produces a special <em>invoker method handle</em> which can be used to
1930 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1931 * The resulting invoker will have a type which is
1932 * exactly equal to the desired type, except that it will accept
1933 * an additional leading argument of type {@code MethodHandle}.
1934 * <p>
1935 * Before invoking its target, if the target differs from the expected type,
1936 * the invoker will apply reference casts as
1937 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1938 * Similarly, the return value will be converted as necessary.
1939 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1940 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1941 * <p>
1942 * This method is equivalent to the following code (though it may be more efficient):
1943 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1944 * <p style="font-size:smaller;">
1945 * <em>Discussion:</em>
1946 * A {@linkplain MethodType#genericMethodType general method type} is one which
1947 * mentions only {@code Object} arguments and return values.
1948 * An invoker for such a type is capable of calling any method handle
1949 * of the same arity as the general type.
1950 * <p style="font-size:smaller;">
1951 * <em>(Note: The invoker method is not available via the Core Reflection API.
1952 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1953 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1954 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1955 * <p>
1956 * This method throws no reflective or security exceptions.
1957 * @param type the desired target type
1958 * @return a method handle suitable for invoking any method handle convertible to the given type
1959 * @throws IllegalArgumentException if the resulting method handle's type would have
1960 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1961 */
1962 static public
1963 MethodHandle invoker(MethodType type) {
1964 return type.invokers().genericInvoker();
1965 }
1966
1967 static /*non-public*/
1968 MethodHandle basicInvoker(MethodType type) {
1969 return type.invokers().basicInvoker();
1970 }
1971
1972 /// method handle modification (creation from other method handles)
1973
1974 /**
1975 * Produces a method handle which adapts the type of the
1976 * given method handle to a new type by pairwise argument and return type conversion.
1977 * The original type and new type must have the same number of arguments.
1978 * The resulting method handle is guaranteed to report a type
1979 * which is equal to the desired new type.
1980 * <p>
1981 * If the original type and new type are equal, returns target.
1982 * <p>
1983 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1984 * and some additional conversions are also applied if those conversions fail.
1985 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1986 * if possible, before or instead of any conversions done by {@code asType}:
1987 * <ul>
1988 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1989 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1990 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1991 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1992 * the boolean is converted to a byte value, 1 for true, 0 for false.
1993 * (This treatment follows the usage of the bytecode verifier.)
1994 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1995 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1996 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1997 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1998 * then a Java casting conversion (JLS 5.5) is applied.
1999 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2000 * widening and/or narrowing.)
2001 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2002 * conversion will be applied at runtime, possibly followed
2003 * by a Java casting conversion (JLS 5.5) on the primitive value,
2004 * possibly followed by a conversion from byte to boolean by testing
2005 * the low-order bit.
2006 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2007 * and if the reference is null at runtime, a zero value is introduced.
2008 * </ul>
2009 * @param target the method handle to invoke after arguments are retyped
2010 * @param newType the expected type of the new method handle
2011 * @return a method handle which delegates to the target after performing
2012 * any necessary argument conversions, and arranges for any
2013 * necessary return value conversions
2014 * @throws NullPointerException if either argument is null
2015 * @throws WrongMethodTypeException if the conversion cannot be made
2016 * @see MethodHandle#asType
2017 */
2018 public static
2019 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2020 if (!target.type().isCastableTo(newType)) {
2021 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
2022 }
2023 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
2024 }
2025
2026 /**
2027 * Produces a method handle which adapts the calling sequence of the
2028 * given method handle to a new type, by reordering the arguments.
2029 * The resulting method handle is guaranteed to report a type
2030 * which is equal to the desired new type.
2031 * <p>
2032 * The given array controls the reordering.
2033 * Call {@code #I} the number of incoming parameters (the value
2034 * {@code newType.parameterCount()}, and call {@code #O} the number
2035 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2036 * Then the length of the reordering array must be {@code #O},
2037 * and each element must be a non-negative number less than {@code #I}.
2038 * For every {@code N} less than {@code #O}, the {@code N}-th
2039 * outgoing argument will be taken from the {@code I}-th incoming
2040 * argument, where {@code I} is {@code reorder[N]}.
2041 * <p>
2042 * No argument or return value conversions are applied.
2043 * The type of each incoming argument, as determined by {@code newType},
2044 * must be identical to the type of the corresponding outgoing parameter
2045 * or parameters in the target method handle.
2046 * The return type of {@code newType} must be identical to the return
2047 * type of the original target.
2048 * <p>
2049 * The reordering array need not specify an actual permutation.
2050 * An incoming argument will be duplicated if its index appears
2051 * more than once in the array, and an incoming argument will be dropped
2052 * if its index does not appear in the array.
2053 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2054 * incoming arguments which are not mentioned in the reordering array
2055 * are may be any type, as determined only by {@code newType}.
2056 * <blockquote><pre>{@code
2057 import static java.lang.invoke.MethodHandles.*;
2058 import static java.lang.invoke.MethodType.*;
2059 ...
2060 MethodType intfn1 = methodType(int.class, int.class);
2061 MethodType intfn2 = methodType(int.class, int.class, int.class);
2062 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2063 assert(sub.type().equals(intfn2));
2064 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2065 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2066 assert((int)rsub.invokeExact(1, 100) == 99);
2067 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2068 assert(add.type().equals(intfn2));
2069 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2070 assert(twice.type().equals(intfn1));
2071 assert((int)twice.invokeExact(21) == 42);
2072 * }</pre></blockquote>
2073 * @param target the method handle to invoke after arguments are reordered
2074 * @param newType the expected type of the new method handle
2075 * @param reorder an index array which controls the reordering
2076 * @return a method handle which delegates to the target after it
2077 * drops unused arguments and moves and/or duplicates the other arguments
2078 * @throws NullPointerException if any argument is null
2079 * @throws IllegalArgumentException if the index array length is not equal to
2080 * the arity of the target, or if any index array element
2081 * not a valid index for a parameter of {@code newType},
2082 * or if two corresponding parameter types in
2083 * {@code target.type()} and {@code newType} are not identical,
2084 */
2085 public static
2086 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2087 reorder = reorder.clone();
2088 permuteArgumentChecks(reorder, newType, target.type());
2089 // first detect dropped arguments and handle them separately
2090 MethodHandle originalTarget = target;
2091 int newArity = newType.parameterCount();
2092 for (int dropIdx; (dropIdx = findFirstDrop(reorder, newArity)) >= 0; ) {
2093 // dropIdx is missing from reorder; add it in at the end
2094 int oldArity = reorder.length;
2095 target = dropArguments(target, oldArity, newType.parameterType(dropIdx));
2096 reorder = Arrays.copyOf(reorder, oldArity+1);
2097 reorder[oldArity] = dropIdx;
2098 }
2099 assert(target == originalTarget || permuteArgumentChecks(reorder, newType, target.type()));
2100 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2101 BoundMethodHandle result = target.rebind();
2102 LambdaForm form = result.form.permuteArguments(1, reorder, basicTypes(newType.parameterList()));
2103 return result.copyWith(newType, form);
2104 }
2105
2106 /** Return the first value in [0..newArity-1] that is not present in reorder. */
2107 private static int findFirstDrop(int[] reorder, int newArity) {
2108 final int BIT_LIMIT = 63; // max number of bits in bit mask
2109 if (newArity < BIT_LIMIT) {
2110 long mask = 0;
2111 for (int arg : reorder) {
2112 assert(arg < newArity);
2113 mask |= (1 << arg);
2114 }
2115 if (mask == (1 << newArity) - 1) {
2116 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2117 return -1;
2118 }
2119 // find first zero
2120 long zeroBit = Long.lowestOneBit(~mask);
2121 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2122 assert(zeroPos < newArity);
2123 return zeroPos;
2124 }
2125 BitSet mask = new BitSet(newArity);
2126 for (int arg : reorder) {
2127 assert(arg < newArity);
2128 mask.set(arg);
2129 }
2130 int zeroPos = mask.nextClearBit(0);
2131 if (zeroPos == newArity)
2132 return -1;
2133 return zeroPos;
2134 }
2135
2136 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2137 if (newType.returnType() != oldType.returnType())
2138 throw newIllegalArgumentException("return types do not match",
2139 oldType, newType);
2140 if (reorder.length == oldType.parameterCount()) {
2141 int limit = newType.parameterCount();
2142 boolean bad = false;
2143 for (int j = 0; j < reorder.length; j++) {
2144 int i = reorder[j];
2145 if (i < 0 || i >= limit) {
2146 bad = true; break;
2147 }
2148 Class<?> src = newType.parameterType(i);
2149 Class<?> dst = oldType.parameterType(j);
2150 if (src != dst)
2151 throw newIllegalArgumentException("parameter types do not match after reorder",
2152 oldType, newType);
2153 }
2154 if (!bad) return true;
2155 }
2156 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2157 }
2158
2159 /**
2160 * Produces a method handle of the requested return type which returns the given
2161 * constant value every time it is invoked.
2162 * <p>
2163 * Before the method handle is returned, the passed-in value is converted to the requested type.
2164 * If the requested type is primitive, widening primitive conversions are attempted,
2165 * else reference conversions are attempted.
2166 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2167 * @param type the return type of the desired method handle
2168 * @param value the value to return
2169 * @return a method handle of the given return type and no arguments, which always returns the given value
2170 * @throws NullPointerException if the {@code type} argument is null
2171 * @throws ClassCastException if the value cannot be converted to the required return type
2172 * @throws IllegalArgumentException if the given type is {@code void.class}
2173 */
2174 public static
2175 MethodHandle constant(Class<?> type, Object value) {
2176 if (type.isPrimitive()) {
2177 if (type == void.class)
2178 throw newIllegalArgumentException("void type");
2179 Wrapper w = Wrapper.forPrimitiveType(type);
2180 return insertArguments(identity(type), 0, w.convert(value, type));
2181 } else {
2182 return identity(type).bindTo(type.cast(value));
2183 }
2184 }
2185
2186 /**
2187 * Produces a method handle which returns its sole argument when invoked.
2188 * @param type the type of the sole parameter and return value of the desired method handle
2189 * @return a unary method handle which accepts and returns the given type
2190 * @throws NullPointerException if the argument is null
2191 * @throws IllegalArgumentException if the given type is {@code void.class}
2192 */
2193 public static
2194 MethodHandle identity(Class<?> type) {
2195 if (type == void.class)
2196 throw newIllegalArgumentException("void type");
2197 else if (type == Object.class)
2198 return ValueConversions.identity();
2199 else if (type.isPrimitive())
2200 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
2201 else
2202 return MethodHandleImpl.makeReferenceIdentity(type);
2203 }
2204
2205 /**
2206 * Provides a target method handle with one or more <em>bound arguments</em>
2207 * in advance of the method handle's invocation.
2208 * The formal parameters to the target corresponding to the bound
2209 * arguments are called <em>bound parameters</em>.
2210 * Returns a new method handle which saves away the bound arguments.
2211 * When it is invoked, it receives arguments for any non-bound parameters,
2212 * binds the saved arguments to their corresponding parameters,
2213 * and calls the original target.
2214 * <p>
2215 * The type of the new method handle will drop the types for the bound
2216 * parameters from the original target type, since the new method handle
2217 * will no longer require those arguments to be supplied by its callers.
2218 * <p>
2219 * Each given argument object must match the corresponding bound parameter type.
2220 * If a bound parameter type is a primitive, the argument object
2221 * must be a wrapper, and will be unboxed to produce the primitive value.
2222 * <p>
2223 * The {@code pos} argument selects which parameters are to be bound.
2224 * It may range between zero and <i>N-L</i> (inclusively),
2225 * where <i>N</i> is the arity of the target method handle
2226 * and <i>L</i> is the length of the values array.
2227 * @param target the method handle to invoke after the argument is inserted
2228 * @param pos where to insert the argument (zero for the first)
2229 * @param values the series of arguments to insert
2230 * @return a method handle which inserts an additional argument,
2231 * before calling the original method handle
2232 * @throws NullPointerException if the target or the {@code values} array is null
2233 * @see MethodHandle#bindTo
2234 */
2235 public static
2236 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2237 int insCount = values.length;
2238 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
2239 if (insCount == 0) return target;
2240 BoundMethodHandle result = target.rebind();
2241 for (int i = 0; i < insCount; i++) {
2242 Object value = values[i];
2243 Class<?> ptype = ptypes[pos+i];
2244 if (ptype.isPrimitive()) {
2245 result = insertArgumentPrimitive(result, pos, ptype, value);
2246 } else {
2247 value = ptype.cast(value); // throw CCE if needed
2248 result = result.bindArgumentL(pos, value);
2249 }
2250 }
2251 return result;
2252 }
2253
2254 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
2255 Class<?> ptype, Object value) {
2256 Wrapper w = Wrapper.forPrimitiveType(ptype);
2257 // perform unboxing and/or primitive conversion
2258 value = w.convert(value, ptype);
2259 switch (w) {
2260 case INT: return result.bindArgumentI(pos, (int)value);
2261 case LONG: return result.bindArgumentJ(pos, (long)value);
2262 case FLOAT: return result.bindArgumentF(pos, (float)value);
2263 case DOUBLE: return result.bindArgumentD(pos, (double)value);
2264 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
2265 }
2266 }
2267
2268 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
2269 MethodType oldType = target.type();
2270 int outargs = oldType.parameterCount();
2271 int inargs = outargs - insCount;
2272 if (inargs < 0)
2273 throw newIllegalArgumentException("too many values to insert");
2274 if (pos < 0 || pos > inargs)
2275 throw newIllegalArgumentException("no argument type to append");
2276 return oldType.ptypes();
2277 }
2278
2279 /**
2280 * Produces a method handle which will discard some dummy arguments
2281 * before calling some other specified <i>target</i> method handle.
2282 * The type of the new method handle will be the same as the target's type,
2283 * except it will also include the dummy argument types,
2284 * at some given position.
2285 * <p>
2286 * The {@code pos} argument may range between zero and <i>N</i>,
2287 * where <i>N</i> is the arity of the target.
2288 * If {@code pos} is zero, the dummy arguments will precede
2289 * the target's real arguments; if {@code pos} is <i>N</i>
2290 * they will come after.
2291 * <p>
2292 * <b>Example:</b>
2293 * <blockquote><pre>{@code
2294 import static java.lang.invoke.MethodHandles.*;
2295 import static java.lang.invoke.MethodType.*;
2296 ...
2297 MethodHandle cat = lookup().findVirtual(String.class,
2298 "concat", methodType(String.class, String.class));
2299 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2300 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2301 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2302 assertEquals(bigType, d0.type());
2303 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2304 * }</pre></blockquote>
2305 * <p>
2306 * This method is also equivalent to the following code:
2307 * <blockquote><pre>
2308 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2309 * </pre></blockquote>
2310 * @param target the method handle to invoke after the arguments are dropped
2311 * @param valueTypes the type(s) of the argument(s) to drop
2312 * @param pos position of first argument to drop (zero for the leftmost)
2313 * @return a method handle which drops arguments of the given types,
2314 * before calling the original method handle
2315 * @throws NullPointerException if the target is null,
2316 * or if the {@code valueTypes} list or any of its elements is null
2317 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2318 * or if {@code pos} is negative or greater than the arity of the target,
2319 * or if the new method handle's type would have too many parameters
2320 */
2321 public static
2322 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2323 MethodType oldType = target.type(); // get NPE
2324 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
2325 if (dropped == 0) return target;
2326 BoundMethodHandle result = target.rebind();
2327 LambdaForm lform = result.form;
2328 lform = lform.addArguments(pos, valueTypes);
2329 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
2330 result = result.copyWith(newType, lform);
2331 return result;
2332 }
2333
2334 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
2335 int dropped = valueTypes.size();
2336 MethodType.checkSlotCount(dropped);
2337 int outargs = oldType.parameterCount();
2338 int inargs = outargs + dropped;
2339 if (pos < 0 || pos > outargs)
2340 throw newIllegalArgumentException("no argument type to remove"
2341 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
2342 );
2343 return dropped;
2344 }
2345
2346 /**
2347 * Produces a method handle which will discard some dummy arguments
2348 * before calling some other specified <i>target</i> method handle.
2349 * The type of the new method handle will be the same as the target's type,
2350 * except it will also include the dummy argument types,
2351 * at some given position.
2352 * <p>
2353 * The {@code pos} argument may range between zero and <i>N</i>,
2354 * where <i>N</i> is the arity of the target.
2355 * If {@code pos} is zero, the dummy arguments will precede
2356 * the target's real arguments; if {@code pos} is <i>N</i>
2357 * they will come after.
2358 * <p>
2359 * <b>Example:</b>
2360 * <blockquote><pre>{@code
2361 import static java.lang.invoke.MethodHandles.*;
2362 import static java.lang.invoke.MethodType.*;
2363 ...
2364 MethodHandle cat = lookup().findVirtual(String.class,
2365 "concat", methodType(String.class, String.class));
2366 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2367 MethodHandle d0 = dropArguments(cat, 0, String.class);
2368 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2369 MethodHandle d1 = dropArguments(cat, 1, String.class);
2370 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2371 MethodHandle d2 = dropArguments(cat, 2, String.class);
2372 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2373 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2374 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2375 * }</pre></blockquote>
2376 * <p>
2377 * This method is also equivalent to the following code:
2378 * <blockquote><pre>
2379 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2380 * </pre></blockquote>
2381 * @param target the method handle to invoke after the arguments are dropped
2382 * @param valueTypes the type(s) of the argument(s) to drop
2383 * @param pos position of first argument to drop (zero for the leftmost)
2384 * @return a method handle which drops arguments of the given types,
2385 * before calling the original method handle
2386 * @throws NullPointerException if the target is null,
2387 * or if the {@code valueTypes} array or any of its elements is null
2388 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2389 * or if {@code pos} is negative or greater than the arity of the target,
2390 * or if the new method handle's type would have
2391 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2392 */
2393 public static
2394 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2395 return dropArguments(target, pos, Arrays.asList(valueTypes));
2396 }
2397
2398 /**
2399 * Adapts a target method handle by pre-processing
2400 * one or more of its arguments, each with its own unary filter function,
2401 * and then calling the target with each pre-processed argument
2402 * replaced by the result of its corresponding filter function.
2403 * <p>
2404 * The pre-processing is performed by one or more method handles,
2405 * specified in the elements of the {@code filters} array.
2406 * The first element of the filter array corresponds to the {@code pos}
2407 * argument of the target, and so on in sequence.
2408 * <p>
2409 * Null arguments in the array are treated as identity functions,
2410 * and the corresponding arguments left unchanged.
2411 * (If there are no non-null elements in the array, the original target is returned.)
2412 * Each filter is applied to the corresponding argument of the adapter.
2413 * <p>
2414 * If a filter {@code F} applies to the {@code N}th argument of
2415 * the target, then {@code F} must be a method handle which
2416 * takes exactly one argument. The type of {@code F}'s sole argument
2417 * replaces the corresponding argument type of the target
2418 * in the resulting adapted method handle.
2419 * The return type of {@code F} must be identical to the corresponding
2420 * parameter type of the target.
2421 * <p>
2422 * It is an error if there are elements of {@code filters}
2423 * (null or not)
2424 * which do not correspond to argument positions in the target.
2425 * <p><b>Example:</b>
2426 * <blockquote><pre>{@code
2427 import static java.lang.invoke.MethodHandles.*;
2428 import static java.lang.invoke.MethodType.*;
2429 ...
2430 MethodHandle cat = lookup().findVirtual(String.class,
2431 "concat", methodType(String.class, String.class));
2432 MethodHandle upcase = lookup().findVirtual(String.class,
2433 "toUpperCase", methodType(String.class));
2434 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2435 MethodHandle f0 = filterArguments(cat, 0, upcase);
2436 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2437 MethodHandle f1 = filterArguments(cat, 1, upcase);
2438 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2439 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2440 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2441 * }</pre></blockquote>
2442 * <p> Here is pseudocode for the resulting adapter:
2443 * <blockquote><pre>{@code
2444 * V target(P... p, A[i]... a[i], B... b);
2445 * A[i] filter[i](V[i]);
2446 * T adapter(P... p, V[i]... v[i], B... b) {
2447 * return target(p..., f[i](v[i])..., b...);
2448 * }
2449 * }</pre></blockquote>
2450 *
2451 * @param target the method handle to invoke after arguments are filtered
2452 * @param pos the position of the first argument to filter
2453 * @param filters method handles to call initially on filtered arguments
2454 * @return method handle which incorporates the specified argument filtering logic
2455 * @throws NullPointerException if the target is null
2456 * or if the {@code filters} array is null
2457 * @throws IllegalArgumentException if a non-null element of {@code filters}
2458 * does not match a corresponding argument type of target as described above,
2459 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2460 * or if the resulting method handle's type would have
2461 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2462 */
2463 public static
2464 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2465 MethodType targetType = target.type();
2466 MethodHandle adapter = target;
2467 MethodType adapterType = null;
2468 assert((adapterType = targetType) != null);
2469 int maxPos = targetType.parameterCount();
2470 if (pos + filters.length > maxPos)
2471 throw newIllegalArgumentException("too many filters");
2472 int curPos = pos-1; // pre-incremented
2473 for (MethodHandle filter : filters) {
2474 curPos += 1;
2475 if (filter == null) continue; // ignore null elements of filters
2476 adapter = filterArgument(adapter, curPos, filter);
2477 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
2478 }
2479 assert(adapterType.equals(adapter.type()));
2480 return adapter;
2481 }
2482
2483 /*non-public*/ static
2484 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2485 MethodType targetType = target.type();
2486 MethodType filterType = filter.type();
2487 if (filterType.parameterCount() != 1
2488 || filterType.returnType() != targetType.parameterType(pos))
2489 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2490 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2491 }
2492
2493 /**
2494 * Adapts a target method handle by pre-processing
2495 * a sub-sequence of its arguments with a filter (another method handle).
2496 * The pre-processed arguments are replaced by the result (if any) of the
2497 * filter function.
2498 * The target is then called on the modified (usually shortened) argument list.
2499 * <p>
2500 * If the filter returns a value, the target must accept that value as
2501 * its argument in position {@code pos}, preceded and/or followed by
2502 * any arguments not passed to the filter.
2503 * If the filter returns void, the target must accept all arguments
2504 * not passed to the filter.
2505 * No arguments are reordered, and a result returned from the filter
2506 * replaces (in order) the whole subsequence of arguments originally
2507 * passed to the adapter.
2508 * <p>
2509 * The argument types (if any) of the filter
2510 * replace zero or one argument types of the target, at position {@code pos},
2511 * in the resulting adapted method handle.
2512 * The return type of the filter (if any) must be identical to the
2513 * argument type of the target at position {@code pos}, and that target argument
2514 * is supplied by the return value of the filter.
2515 * <p>
2516 * In all cases, {@code pos} must be greater than or equal to zero, and
2517 * {@code pos} must also be less than or equal to the target's arity.
2518 * <p><b>Example:</b>
2519 * <blockquote><pre>{@code
2520 import static java.lang.invoke.MethodHandles.*;
2521 import static java.lang.invoke.MethodType.*;
2522 ...
2523 MethodHandle deepToString = publicLookup()
2524 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2525
2526 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2527 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2528
2529 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2530 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2531
2532 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2533 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2534 assertEquals("[top, [up, down], strange]",
2535 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2536
2537 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2538 assertEquals("[top, [up, down], [strange]]",
2539 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2540
2541 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2542 assertEquals("[top, [[up, down, strange], charm], bottom]",
2543 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2544 * }</pre></blockquote>
2545 * <p> Here is pseudocode for the resulting adapter:
2546 * <blockquote><pre>{@code
2547 * T target(A...,V,C...);
2548 * V filter(B...);
2549 * T adapter(A... a,B... b,C... c) {
2550 * V v = filter(b...);
2551 * return target(a...,v,c...);
2552 * }
2553 * // and if the filter has no arguments:
2554 * T target2(A...,V,C...);
2555 * V filter2();
2556 * T adapter2(A... a,C... c) {
2557 * V v = filter2();
2558 * return target2(a...,v,c...);
2559 * }
2560 * // and if the filter has a void return:
2561 * T target3(A...,C...);
2562 * void filter3(B...);
2563 * void adapter3(A... a,B... b,C... c) {
2564 * filter3(b...);
2565 * return target3(a...,c...);
2566 * }
2567 * }</pre></blockquote>
2568 * <p>
2569 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2570 * one which first "folds" the affected arguments, and then drops them, in separate
2571 * steps as follows:
2572 * <blockquote><pre>{@code
2573 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2574 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2575 * }</pre></blockquote>
2576 * If the target method handle consumes no arguments besides than the result
2577 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2578 * is equivalent to {@code filterReturnValue(coll, mh)}.
2579 * If the filter method handle {@code coll} consumes one argument and produces
2580 * a non-void result, then {@code collectArguments(mh, N, coll)}
2581 * is equivalent to {@code filterArguments(mh, N, coll)}.
2582 * Other equivalences are possible but would require argument permutation.
2583 *
2584 * @param target the method handle to invoke after filtering the subsequence of arguments
2585 * @param pos the position of the first adapter argument to pass to the filter,
2586 * and/or the target argument which receives the result of the filter
2587 * @param filter method handle to call on the subsequence of arguments
2588 * @return method handle which incorporates the specified argument subsequence filtering logic
2589 * @throws NullPointerException if either argument is null
2590 * @throws IllegalArgumentException if the return type of {@code filter}
2591 * is non-void and is not the same as the {@code pos} argument of the target,
2592 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2593 * or if the resulting method handle's type would have
2594 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2595 * @see MethodHandles#foldArguments
2596 * @see MethodHandles#filterArguments
2597 * @see MethodHandles#filterReturnValue
2598 */
2599 public static
2600 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2601 MethodType targetType = target.type();
2602 MethodType filterType = filter.type();
2603 if (filterType.returnType() != void.class &&
2604 filterType.returnType() != targetType.parameterType(pos))
2605 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2606 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2607 }
2608
2609 /**
2610 * Adapts a target method handle by post-processing
2611 * its return value (if any) with a filter (another method handle).
2612 * The result of the filter is returned from the adapter.
2613 * <p>
2614 * If the target returns a value, the filter must accept that value as
2615 * its only argument.
2616 * If the target returns void, the filter must accept no arguments.
2617 * <p>
2618 * The return type of the filter
2619 * replaces the return type of the target
2620 * in the resulting adapted method handle.
2621 * The argument type of the filter (if any) must be identical to the
2622 * return type of the target.
2623 * <p><b>Example:</b>
2624 * <blockquote><pre>{@code
2625 import static java.lang.invoke.MethodHandles.*;
2626 import static java.lang.invoke.MethodType.*;
2627 ...
2628 MethodHandle cat = lookup().findVirtual(String.class,
2629 "concat", methodType(String.class, String.class));
2630 MethodHandle length = lookup().findVirtual(String.class,
2631 "length", methodType(int.class));
2632 System.out.println((String) cat.invokeExact("x", "y")); // xy
2633 MethodHandle f0 = filterReturnValue(cat, length);
2634 System.out.println((int) f0.invokeExact("x", "y")); // 2
2635 * }</pre></blockquote>
2636 * <p> Here is pseudocode for the resulting adapter:
2637 * <blockquote><pre>{@code
2638 * V target(A...);
2639 * T filter(V);
2640 * T adapter(A... a) {
2641 * V v = target(a...);
2642 * return filter(v);
2643 * }
2644 * // and if the target has a void return:
2645 * void target2(A...);
2646 * T filter2();
2647 * T adapter2(A... a) {
2648 * target2(a...);
2649 * return filter2();
2650 * }
2651 * // and if the filter has a void return:
2652 * V target3(A...);
2653 * void filter3(V);
2654 * void adapter3(A... a) {
2655 * V v = target3(a...);
2656 * filter3(v);
2657 * }
2658 * }</pre></blockquote>
2659 * @param target the method handle to invoke before filtering the return value
2660 * @param filter method handle to call on the return value
2661 * @return method handle which incorporates the specified return value filtering logic
2662 * @throws NullPointerException if either argument is null
2663 * @throws IllegalArgumentException if the argument list of {@code filter}
2664 * does not match the return type of target as described above
2665 */
2666 public static
2667 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2668 MethodType targetType = target.type();
2669 MethodType filterType = filter.type();
2670 Class<?> rtype = targetType.returnType();
2671 int filterValues = filterType.parameterCount();
2672 if (filterValues == 0
2673 ? (rtype != void.class)
2674 : (rtype != filterType.parameterType(0)))
2675 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2676 // result = fold( lambda(retval, arg...) { filter(retval) },
2677 // lambda( arg...) { target(arg...) } )
2678 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2679 }
2680
2681 /**
2682 * Adapts a target method handle by pre-processing
2683 * some of its arguments, and then calling the target with
2684 * the result of the pre-processing, inserted into the original
2685 * sequence of arguments.
2686 * <p>
2687 * The pre-processing is performed by {@code combiner}, a second method handle.
2688 * Of the arguments passed to the adapter, the first {@code N} arguments
2689 * are copied to the combiner, which is then called.
2690 * (Here, {@code N} is defined as the parameter count of the combiner.)
2691 * After this, control passes to the target, with any result
2692 * from the combiner inserted before the original {@code N} incoming
2693 * arguments.
2694 * <p>
2695 * If the combiner returns a value, the first parameter type of the target
2696 * must be identical with the return type of the combiner, and the next
2697 * {@code N} parameter types of the target must exactly match the parameters
2698 * of the combiner.
2699 * <p>
2700 * If the combiner has a void return, no result will be inserted,
2701 * and the first {@code N} parameter types of the target
2702 * must exactly match the parameters of the combiner.
2703 * <p>
2704 * The resulting adapter is the same type as the target, except that the
2705 * first parameter type is dropped,
2706 * if it corresponds to the result of the combiner.
2707 * <p>
2708 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2709 * that either the combiner or the target does not wish to receive.
2710 * If some of the incoming arguments are destined only for the combiner,
2711 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2712 * arguments will not need to be live on the stack on entry to the
2713 * target.)
2714 * <p><b>Example:</b>
2715 * <blockquote><pre>{@code
2716 import static java.lang.invoke.MethodHandles.*;
2717 import static java.lang.invoke.MethodType.*;
2718 ...
2719 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2720 "println", methodType(void.class, String.class))
2721 .bindTo(System.out);
2722 MethodHandle cat = lookup().findVirtual(String.class,
2723 "concat", methodType(String.class, String.class));
2724 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2725 MethodHandle catTrace = foldArguments(cat, trace);
2726 // also prints "boo":
2727 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2728 * }</pre></blockquote>
2729 * <p> Here is pseudocode for the resulting adapter:
2730 * <blockquote><pre>{@code
2731 * // there are N arguments in A...
2732 * T target(V, A[N]..., B...);
2733 * V combiner(A...);
2734 * T adapter(A... a, B... b) {
2735 * V v = combiner(a...);
2736 * return target(v, a..., b...);
2737 * }
2738 * // and if the combiner has a void return:
2739 * T target2(A[N]..., B...);
2740 * void combiner2(A...);
2741 * T adapter2(A... a, B... b) {
2742 * combiner2(a...);
2743 * return target2(a..., b...);
2744 * }
2745 * }</pre></blockquote>
2746 * @param target the method handle to invoke after arguments are combined
2747 * @param combiner method handle to call initially on the incoming arguments
2748 * @return method handle which incorporates the specified argument folding logic
2749 * @throws NullPointerException if either argument is null
2750 * @throws IllegalArgumentException if {@code combiner}'s return type
2751 * is non-void and not the same as the first argument type of
2752 * the target, or if the initial {@code N} argument types
2753 * of the target
2754 * (skipping one matching the {@code combiner}'s return type)
2755 * are not identical with the argument types of {@code combiner}
2756 */
2757 public static
2758 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2759 int pos = 0;
2760 MethodType targetType = target.type();
2761 MethodType combinerType = combiner.type();
2762 int foldPos = pos;
2763 int foldArgs = combinerType.parameterCount();
2764 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2765 int afterInsertPos = foldPos + foldVals;
2766 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2767 if (ok && !(combinerType.parameterList()
2768 .equals(targetType.parameterList().subList(afterInsertPos,
2769 afterInsertPos + foldArgs))))
2770 ok = false;
2771 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2772 ok = false;
2773 if (!ok)
2774 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2775 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2776 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2777 }
2778
2779 /**
2780 * Makes a method handle which adapts a target method handle,
2781 * by guarding it with a test, a boolean-valued method handle.
2782 * If the guard fails, a fallback handle is called instead.
2783 * All three method handles must have the same corresponding
2784 * argument and return types, except that the return type
2785 * of the test must be boolean, and the test is allowed
2786 * to have fewer arguments than the other two method handles.
2787 * <p> Here is pseudocode for the resulting adapter:
2788 * <blockquote><pre>{@code
2789 * boolean test(A...);
2790 * T target(A...,B...);
2791 * T fallback(A...,B...);
2792 * T adapter(A... a,B... b) {
2793 * if (test(a...))
2794 * return target(a..., b...);
2795 * else
2796 * return fallback(a..., b...);
2797 * }
2798 * }</pre></blockquote>
2799 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2800 * be modified by execution of the test, and so are passed unchanged
2801 * from the caller to the target or fallback as appropriate.
2802 * @param test method handle used for test, must return boolean
2803 * @param target method handle to call if test passes
2804 * @param fallback method handle to call if test fails
2805 * @return method handle which incorporates the specified if/then/else logic
2806 * @throws NullPointerException if any argument is null
2807 * @throws IllegalArgumentException if {@code test} does not return boolean,
2808 * or if all three method types do not match (with the return
2809 * type of {@code test} changed to match that of the target).
2810 */
2811 public static
2812 MethodHandle guardWithTest(MethodHandle test,
2813 MethodHandle target,
2814 MethodHandle fallback) {
2815 MethodType gtype = test.type();
2816 MethodType ttype = target.type();
2817 MethodType ftype = fallback.type();
2818 if (!ttype.equals(ftype))
2819 throw misMatchedTypes("target and fallback types", ttype, ftype);
2820 if (gtype.returnType() != boolean.class)
2821 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2822 List<Class<?>> targs = ttype.parameterList();
2823 List<Class<?>> gargs = gtype.parameterList();
2824 if (!targs.equals(gargs)) {
2825 int gpc = gargs.size(), tpc = targs.size();
2826 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2827 throw misMatchedTypes("target and test types", ttype, gtype);
2828 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2829 gtype = test.type();
2830 }
2831 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2832 }
2833
2834 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2835 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2836 }
2837
2838 /**
2839 * Makes a method handle which adapts a target method handle,
2840 * by running it inside an exception handler.
2841 * If the target returns normally, the adapter returns that value.
2842 * If an exception matching the specified type is thrown, the fallback
2843 * handle is called instead on the exception, plus the original arguments.
2844 * <p>
2845 * The target and handler must have the same corresponding
2846 * argument and return types, except that handler may omit trailing arguments
2847 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2848 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2849 * <p> Here is pseudocode for the resulting adapter:
2850 * <blockquote><pre>{@code
2851 * T target(A..., B...);
2852 * T handler(ExType, A...);
2853 * T adapter(A... a, B... b) {
2854 * try {
2855 * return target(a..., b...);
2856 * } catch (ExType ex) {
2857 * return handler(ex, a...);
2858 * }
2859 * }
2860 * }</pre></blockquote>
2861 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2862 * be modified by execution of the target, and so are passed unchanged
2863 * from the caller to the handler, if the handler is invoked.
2864 * <p>
2865 * The target and handler must return the same type, even if the handler
2866 * always throws. (This might happen, for instance, because the handler
2867 * is simulating a {@code finally} clause).
2868 * To create such a throwing handler, compose the handler creation logic
2869 * with {@link #throwException throwException},
2870 * in order to create a method handle of the correct return type.
2871 * @param target method handle to call
2872 * @param exType the type of exception which the handler will catch
2873 * @param handler method handle to call if a matching exception is thrown
2874 * @return method handle which incorporates the specified try/catch logic
2875 * @throws NullPointerException if any argument is null
2876 * @throws IllegalArgumentException if {@code handler} does not accept
2877 * the given exception type, or if the method handle types do
2878 * not match in their return types and their
2879 * corresponding parameters
2880 */
2881 public static
2882 MethodHandle catchException(MethodHandle target,
2883 Class<? extends Throwable> exType,
2884 MethodHandle handler) {
2885 MethodType ttype = target.type();
2886 MethodType htype = handler.type();
2887 if (htype.parameterCount() < 1 ||
2888 !htype.parameterType(0).isAssignableFrom(exType))
2889 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2890 if (htype.returnType() != ttype.returnType())
2891 throw misMatchedTypes("target and handler return types", ttype, htype);
2892 List<Class<?>> targs = ttype.parameterList();
2893 List<Class<?>> hargs = htype.parameterList();
2894 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2895 if (!targs.equals(hargs)) {
2896 int hpc = hargs.size(), tpc = targs.size();
2897 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2898 throw misMatchedTypes("target and handler types", ttype, htype);
2899 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2900 htype = handler.type();
2901 }
2902 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2903 }
2904
2905 /**
2906 * Produces a method handle which will throw exceptions of the given {@code exType}.
2907 * The method handle will accept a single argument of {@code exType},
2908 * and immediately throw it as an exception.
2909 * The method type will nominally specify a return of {@code returnType}.
2910 * The return type may be anything convenient: It doesn't matter to the
2911 * method handle's behavior, since it will never return normally.
2912 * @param returnType the return type of the desired method handle
2913 * @param exType the parameter type of the desired method handle
2914 * @return method handle which can throw the given exceptions
2915 * @throws NullPointerException if either argument is null
2916 */
2917 public static
2918 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2919 if (!Throwable.class.isAssignableFrom(exType))
2920 throw new ClassCastException(exType.getName());
2921 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2922 }
2923 }