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 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.util.List;
30 import java.util.ArrayList;
31 import java.util.Arrays;
32
33 import sun.invoke.util.ValueConversions;
34 import sun.invoke.util.VerifyAccess;
35 import sun.invoke.util.Wrapper;
36 import sun.reflect.CallerSensitive;
37 import sun.reflect.Reflection;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40 import java.lang.invoke.LambdaForm.BasicType;
41 import static java.lang.invoke.LambdaForm.BasicType.*;
42 import static java.lang.invoke.MethodHandleStatics.*;
43 import static java.lang.invoke.MethodHandleNatives.Constants.*;
44 import java.util.concurrent.ConcurrentHashMap;
45
46 /**
47 * This class consists exclusively of static methods that operate on or return
48 * method handles. They fall into several categories:
49 * <ul>
50 * <li>Lookup methods which help create method handles for methods and fields.
51 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
52 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
53 * </ul>
54 *
55 * @author John Rose, JSR 292 EG
56 * @since 1.7
57 */
58 public class MethodHandles {
59
60 private MethodHandles() { } // do not instantiate
61
62 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
63 static { MethodHandleImpl.initStatics(); }
64 // See IMPL_LOOKUP below.
65
66 //// Method handle creation from ordinary methods.
67
68 /**
69 * Returns a {@link Lookup lookup object} with
70 * full capabilities to emulate all supported bytecode behaviors of the caller.
71 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
72 * Factory methods on the lookup object can create
73 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
74 * for any member that the caller has access to via bytecodes,
75 * including protected and private fields and methods.
76 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
77 * Do not store it in place where untrusted code can access it.
78 * <p>
79 * This method is caller sensitive, which means that it may return different
80 * values to different callers.
81 * <p>
82 * For any given caller class {@code C}, the lookup object returned by this call
83 * has equivalent capabilities to any lookup object
84 * supplied by the JVM to the bootstrap method of an
85 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
86 * executing in the same caller class {@code C}.
87 * @return a lookup object for the caller of this method, with private access
88 */
89 @CallerSensitive
90 public static Lookup lookup() {
91 return new Lookup(Reflection.getCallerClass());
92 }
93
94 /**
95 * Returns a {@link Lookup lookup object} which is trusted minimally.
96 * It can only be used to create method handles to
97 * publicly accessible fields and methods.
98 * <p>
99 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
100 * of this lookup object will be {@link java.lang.Object}.
101 *
102 * <p style="font-size:smaller;">
103 * <em>Discussion:</em>
104 * The lookup class can be changed to any other class {@code C} using an expression of the form
105 * {@link Lookup#in publicLookup().in(C.class)}.
106 * Since all classes have equal access to public names,
107 * such a change would confer no new access rights.
108 * A public lookup object is always subject to
109 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
110 * Also, it cannot access
111 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
112 * @return a lookup object which is trusted minimally
113 */
114 public static Lookup publicLookup() {
115 return Lookup.PUBLIC_LOOKUP;
116 }
117
118 /**
119 * Performs an unchecked "crack" of a
120 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
121 * The result is as if the user had obtained a lookup object capable enough
122 * to crack the target method handle, called
123 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
124 * on the target to obtain its symbolic reference, and then called
125 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
126 * to resolve the symbolic reference to a member.
127 * <p>
128 * If there is a security manager, its {@code checkPermission} method
129 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
130 * @param <T> the desired type of the result, either {@link Member} or a subtype
131 * @param target a direct method handle to crack into symbolic reference components
132 * @param expected a class object representing the desired result type {@code T}
133 * @return a reference to the method, constructor, or field object
134 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
135 * @exception NullPointerException if either argument is {@code null}
136 * @exception IllegalArgumentException if the target is not a direct method handle
137 * @exception ClassCastException if the member is not of the expected type
138 * @since 1.8
139 */
140 public static <T extends Member> T
141 reflectAs(Class<T> expected, MethodHandle target) {
142 SecurityManager smgr = System.getSecurityManager();
143 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
144 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
145 return lookup.revealDirect(target).reflectAs(expected, lookup);
146 }
147 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
148 static final private java.security.Permission ACCESS_PERMISSION =
149 new ReflectPermission("suppressAccessChecks");
150
151 /**
152 * A <em>lookup object</em> is a factory for creating method handles,
153 * when the creation requires access checking.
154 * Method handles do not perform
155 * access checks when they are called, but rather when they are created.
156 * Therefore, method handle access
157 * restrictions must be enforced when a method handle is created.
158 * The caller class against which those restrictions are enforced
159 * is known as the {@linkplain #lookupClass lookup class}.
160 * <p>
161 * A lookup class which needs to create method handles will call
162 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
163 * When the {@code Lookup} factory object is created, the identity of the lookup class is
164 * determined, and securely stored in the {@code Lookup} object.
165 * The lookup class (or its delegates) may then use factory methods
166 * on the {@code Lookup} object to create method handles for access-checked members.
167 * This includes all methods, constructors, and fields which are allowed to the lookup class,
168 * even private ones.
169 *
170 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
171 * The factory methods on a {@code Lookup} object correspond to all major
172 * use cases for methods, constructors, and fields.
173 * Each method handle created by a factory method is the functional
174 * equivalent of a particular <em>bytecode behavior</em>.
175 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
176 * Here is a summary of the correspondence between these factory methods and
177 * the behavior the resulting method handles:
178 * <table border=1 cellpadding=5 summary="lookup method behaviors">
179 * <tr>
180 * <th><a name="equiv"></a>lookup expression</th>
181 * <th>member</th>
182 * <th>bytecode behavior</th>
183 * </tr>
184 * <tr>
185 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
186 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
187 * </tr>
188 * <tr>
189 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
190 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
191 * </tr>
192 * <tr>
193 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
194 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
195 * </tr>
196 * <tr>
197 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
198 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
199 * </tr>
200 * <tr>
201 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
202 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
203 * </tr>
204 * <tr>
205 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
206 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
207 * </tr>
208 * <tr>
209 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
210 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
211 * </tr>
212 * <tr>
213 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
214 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
215 * </tr>
216 * <tr>
217 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
218 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
219 * </tr>
220 * <tr>
221 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
222 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
223 * </tr>
224 * <tr>
225 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
226 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
227 * </tr>
228 * <tr>
229 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
230 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
231 * </tr>
232 * <tr>
233 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
234 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
235 * </tr>
236 * </table>
237 *
238 * Here, the type {@code C} is the class or interface being searched for a member,
239 * documented as a parameter named {@code refc} in the lookup methods.
240 * The method type {@code MT} is composed from the return type {@code T}
241 * and the sequence of argument types {@code A*}.
242 * The constructor also has a sequence of argument types {@code A*} and
243 * is deemed to return the newly-created object of type {@code C}.
244 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
245 * The formal parameter {@code this} stands for the self-reference of type {@code C};
246 * if it is present, it is always the leading argument to the method handle invocation.
247 * (In the case of some {@code protected} members, {@code this} may be
248 * restricted in type to the lookup class; see below.)
249 * The name {@code arg} stands for all the other method handle arguments.
250 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
251 * stands for a null reference if the accessed method or field is static,
252 * and {@code this} otherwise.
253 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
254 * for reflective objects corresponding to the given members.
255 * <p>
256 * In cases where the given member is of variable arity (i.e., a method or constructor)
257 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
258 * In all other cases, the returned method handle will be of fixed arity.
259 * <p style="font-size:smaller;">
260 * <em>Discussion:</em>
261 * The equivalence between looked-up method handles and underlying
262 * class members and bytecode behaviors
263 * can break down in a few ways:
264 * <ul style="font-size:smaller;">
265 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
266 * the lookup can still succeed, even when there is no equivalent
267 * Java expression or bytecoded constant.
268 * <li>Likewise, if {@code T} or {@code MT}
269 * is not symbolically accessible from the lookup class's loader,
270 * the lookup can still succeed.
271 * For example, lookups for {@code MethodHandle.invokeExact} and
272 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
273 * <li>If there is a security manager installed, it can forbid the lookup
274 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
275 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
276 * constant is not subject to security manager checks.
277 * <li>If the looked-up method has a
278 * <a href="MethodHandle.html#maxarity">very large arity</a>,
279 * the method handle creation may fail, due to the method handle
280 * type having too many parameters.
281 * </ul>
282 *
283 * <h1><a name="access"></a>Access checking</h1>
284 * Access checks are applied in the factory methods of {@code Lookup},
285 * when a method handle is created.
286 * This is a key difference from the Core Reflection API, since
287 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
288 * performs access checking against every caller, on every call.
289 * <p>
290 * All access checks start from a {@code Lookup} object, which
291 * compares its recorded lookup class against all requests to
292 * create method handles.
293 * A single {@code Lookup} object can be used to create any number
294 * of access-checked method handles, all checked against a single
295 * lookup class.
296 * <p>
297 * A {@code Lookup} object can be shared with other trusted code,
298 * such as a metaobject protocol.
299 * A shared {@code Lookup} object delegates the capability
300 * to create method handles on private members of the lookup class.
301 * Even if privileged code uses the {@code Lookup} object,
302 * the access checking is confined to the privileges of the
303 * original lookup class.
304 * <p>
305 * A lookup can fail, because
306 * the containing class is not accessible to the lookup class, or
307 * because the desired class member is missing, or because the
308 * desired class member is not accessible to the lookup class, or
309 * because the lookup object is not trusted enough to access the member.
310 * In any of these cases, a {@code ReflectiveOperationException} will be
311 * thrown from the attempted lookup. The exact class will be one of
312 * the following:
313 * <ul>
314 * <li>NoSuchMethodException — if a method is requested but does not exist
315 * <li>NoSuchFieldException — if a field is requested but does not exist
316 * <li>IllegalAccessException — if the member exists but an access check fails
317 * </ul>
318 * <p>
319 * In general, the conditions under which a method handle may be
320 * looked up for a method {@code M} are no more restrictive than the conditions
321 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
322 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
323 * a method handle lookup will generally raise a corresponding
324 * checked exception, such as {@code NoSuchMethodException}.
325 * And the effect of invoking the method handle resulting from the lookup
326 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
327 * to executing the compiled, verified, and resolved call to {@code M}.
328 * The same point is true of fields and constructors.
329 * <p style="font-size:smaller;">
330 * <em>Discussion:</em>
331 * Access checks only apply to named and reflected methods,
332 * constructors, and fields.
333 * Other method handle creation methods, such as
334 * {@link MethodHandle#asType MethodHandle.asType},
335 * do not require any access checks, and are used
336 * independently of any {@code Lookup} object.
337 * <p>
338 * If the desired member is {@code protected}, the usual JVM rules apply,
339 * including the requirement that the lookup class must be either be in the
340 * same package as the desired member, or must inherit that member.
341 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
342 * In addition, if the desired member is a non-static field or method
343 * in a different package, the resulting method handle may only be applied
344 * to objects of the lookup class or one of its subclasses.
345 * This requirement is enforced by narrowing the type of the leading
346 * {@code this} parameter from {@code C}
347 * (which will necessarily be a superclass of the lookup class)
348 * to the lookup class itself.
349 * <p>
350 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
351 * that the receiver argument must match both the resolved method <em>and</em>
352 * the current class. Again, this requirement is enforced by narrowing the
353 * type of the leading parameter to the resulting method handle.
354 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
355 * <p>
356 * The JVM represents constructors and static initializer blocks as internal methods
357 * with special names ({@code "<init>"} and {@code "<clinit>"}).
358 * The internal syntax of invocation instructions allows them to refer to such internal
359 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
360 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
361 * <p>
362 * In some cases, access between nested classes is obtained by the Java compiler by creating
363 * an wrapper method to access a private method of another class
364 * in the same top-level declaration.
365 * For example, a nested class {@code C.D}
366 * can access private members within other related classes such as
367 * {@code C}, {@code C.D.E}, or {@code C.B},
368 * but the Java compiler may need to generate wrapper methods in
369 * those related classes. In such cases, a {@code Lookup} object on
370 * {@code C.E} would be unable to those private members.
371 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
372 * which can transform a lookup on {@code C.E} into one on any of those other
373 * classes, without special elevation of privilege.
374 * <p>
375 * The accesses permitted to a given lookup object may be limited,
376 * according to its set of {@link #lookupModes lookupModes},
377 * to a subset of members normally accessible to the lookup class.
378 * For example, the {@link MethodHandles#publicLookup publicLookup}
379 * method produces a lookup object which is only allowed to access
380 * public members in public classes.
381 * The caller sensitive method {@link MethodHandles#lookup lookup}
382 * produces a lookup object with full capabilities relative to
383 * its caller class, to emulate all supported bytecode behaviors.
384 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
385 * with fewer access modes than the original lookup object.
386 *
387 * <p style="font-size:smaller;">
388 * <a name="privacc"></a>
389 * <em>Discussion of private access:</em>
390 * We say that a lookup has <em>private access</em>
391 * if its {@linkplain #lookupModes lookup modes}
392 * include the possibility of accessing {@code private} members.
393 * As documented in the relevant methods elsewhere,
394 * only lookups with private access possess the following capabilities:
395 * <ul style="font-size:smaller;">
396 * <li>access private fields, methods, and constructors of the lookup class
397 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
398 * such as {@code Class.forName}
399 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
400 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
401 * for classes accessible to the lookup class
402 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
403 * within the same package member
404 * </ul>
405 * <p style="font-size:smaller;">
406 * Each of these permissions is a consequence of the fact that a lookup object
407 * with private access can be securely traced back to an originating class,
408 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
409 * can be reliably determined and emulated by method handles.
410 *
411 * <h1><a name="secmgr"></a>Security manager interactions</h1>
412 * Although bytecode instructions can only refer to classes in
413 * a related class loader, this API can search for methods in any
414 * class, as long as a reference to its {@code Class} object is
415 * available. Such cross-loader references are also possible with the
416 * Core Reflection API, and are impossible to bytecode instructions
417 * such as {@code invokestatic} or {@code getfield}.
418 * There is a {@linkplain java.lang.SecurityManager security manager API}
419 * to allow applications to check such cross-loader references.
420 * These checks apply to both the {@code MethodHandles.Lookup} API
421 * and the Core Reflection API
422 * (as found on {@link java.lang.Class Class}).
423 * <p>
424 * If a security manager is present, member lookups are subject to
425 * additional checks.
426 * From one to three calls are made to the security manager.
427 * Any of these calls can refuse access by throwing a
428 * {@link java.lang.SecurityException SecurityException}.
429 * Define {@code smgr} as the security manager,
430 * {@code lookc} as the lookup class of the current lookup object,
431 * {@code refc} as the containing class in which the member
432 * is being sought, and {@code defc} as the class in which the
433 * member is actually defined.
434 * The value {@code lookc} is defined as <em>not present</em>
435 * if the current lookup object does not have
436 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
437 * The calls are made according to the following rules:
438 * <ul>
439 * <li><b>Step 1:</b>
440 * If {@code lookc} is not present, or if its class loader is not
441 * the same as or an ancestor of the class loader of {@code refc},
442 * then {@link SecurityManager#checkPackageAccess
443 * smgr.checkPackageAccess(refcPkg)} is called,
444 * where {@code refcPkg} is the package of {@code refc}.
445 * <li><b>Step 2:</b>
446 * If the retrieved member is not public and
447 * {@code lookc} is not present, then
448 * {@link SecurityManager#checkPermission smgr.checkPermission}
449 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
450 * <li><b>Step 3:</b>
451 * If the retrieved member is not public,
452 * and if {@code lookc} is not present,
453 * and if {@code defc} and {@code refc} are different,
454 * then {@link SecurityManager#checkPackageAccess
455 * smgr.checkPackageAccess(defcPkg)} is called,
456 * where {@code defcPkg} is the package of {@code defc}.
457 * </ul>
458 * Security checks are performed after other access checks have passed.
459 * Therefore, the above rules presuppose a member that is public,
460 * or else that is being accessed from a lookup class that has
461 * rights to access the member.
462 *
463 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
464 * A small number of Java methods have a special property called caller sensitivity.
465 * A <em>caller-sensitive</em> method can behave differently depending on the
466 * identity of its immediate caller.
467 * <p>
468 * If a method handle for a caller-sensitive method is requested,
469 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
470 * but they take account of the lookup class in a special way.
471 * The resulting method handle behaves as if it were called
472 * from an instruction contained in the lookup class,
473 * so that the caller-sensitive method detects the lookup class.
474 * (By contrast, the invoker of the method handle is disregarded.)
475 * Thus, in the case of caller-sensitive methods,
476 * different lookup classes may give rise to
477 * differently behaving method handles.
478 * <p>
479 * In cases where the lookup object is
480 * {@link MethodHandles#publicLookup() publicLookup()},
481 * or some other lookup object without
482 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
483 * the lookup class is disregarded.
484 * In such cases, no caller-sensitive method handle can be created,
485 * access is forbidden, and the lookup fails with an
486 * {@code IllegalAccessException}.
487 * <p style="font-size:smaller;">
488 * <em>Discussion:</em>
489 * For example, the caller-sensitive method
490 * {@link java.lang.Class#forName(String) Class.forName(x)}
491 * can return varying classes or throw varying exceptions,
492 * depending on the class loader of the class that calls it.
493 * A public lookup of {@code Class.forName} will fail, because
494 * there is no reasonable way to determine its bytecode behavior.
495 * <p style="font-size:smaller;">
496 * If an application caches method handles for broad sharing,
497 * it should use {@code publicLookup()} to create them.
498 * If there is a lookup of {@code Class.forName}, it will fail,
499 * and the application must take appropriate action in that case.
500 * It may be that a later lookup, perhaps during the invocation of a
501 * bootstrap method, can incorporate the specific identity
502 * of the caller, making the method accessible.
503 * <p style="font-size:smaller;">
504 * The function {@code MethodHandles.lookup} is caller sensitive
505 * so that there can be a secure foundation for lookups.
506 * Nearly all other methods in the JSR 292 API rely on lookup
507 * objects to check access requests.
508 */
509 public static final
510 class Lookup {
511 /** The class on behalf of whom the lookup is being performed. */
512 private final Class<?> lookupClass;
513
514 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
515 private final int allowedModes;
516
517 /** A single-bit mask representing {@code public} access,
518 * which may contribute to the result of {@link #lookupModes lookupModes}.
519 * The value, {@code 0x01}, happens to be the same as the value of the
520 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
521 */
522 public static final int PUBLIC = Modifier.PUBLIC;
523
524 /** A single-bit mask representing {@code private} access,
525 * which may contribute to the result of {@link #lookupModes lookupModes}.
526 * The value, {@code 0x02}, happens to be the same as the value of the
527 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
528 */
529 public static final int PRIVATE = Modifier.PRIVATE;
530
531 /** A single-bit mask representing {@code protected} access,
532 * which may contribute to the result of {@link #lookupModes lookupModes}.
533 * The value, {@code 0x04}, happens to be the same as the value of the
534 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
535 */
536 public static final int PROTECTED = Modifier.PROTECTED;
537
538 /** A single-bit mask representing {@code package} access (default access),
539 * which may contribute to the result of {@link #lookupModes lookupModes}.
540 * The value is {@code 0x08}, which does not correspond meaningfully to
541 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
542 */
543 public static final int PACKAGE = Modifier.STATIC;
544
545 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
546 private static final int TRUSTED = -1;
547
548 private static int fixmods(int mods) {
549 mods &= (ALL_MODES - PACKAGE);
550 return (mods != 0) ? mods : PACKAGE;
551 }
552
553 /** Tells which class is performing the lookup. It is this class against
554 * which checks are performed for visibility and access permissions.
555 * <p>
556 * The class implies a maximum level of access permission,
557 * but the permissions may be additionally limited by the bitmask
558 * {@link #lookupModes lookupModes}, which controls whether non-public members
559 * can be accessed.
560 * @return the lookup class, on behalf of which this lookup object finds members
561 */
562 public Class<?> lookupClass() {
563 return lookupClass;
564 }
565
566 // This is just for calling out to MethodHandleImpl.
567 private Class<?> lookupClassOrNull() {
568 return (allowedModes == TRUSTED) ? null : lookupClass;
569 }
570
571 /** Tells which access-protection classes of members this lookup object can produce.
572 * The result is a bit-mask of the bits
573 * {@linkplain #PUBLIC PUBLIC (0x01)},
574 * {@linkplain #PRIVATE PRIVATE (0x02)},
575 * {@linkplain #PROTECTED PROTECTED (0x04)},
576 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
577 * <p>
578 * A freshly-created lookup object
579 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
580 * has all possible bits set, since the caller class can access all its own members.
581 * A lookup object on a new lookup class
582 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
583 * may have some mode bits set to zero.
584 * The purpose of this is to restrict access via the new lookup object,
585 * so that it can access only names which can be reached by the original
586 * lookup object, and also by the new lookup class.
587 * @return the lookup modes, which limit the kinds of access performed by this lookup object
588 */
589 public int lookupModes() {
590 return allowedModes & ALL_MODES;
591 }
592
593 /** Embody the current class (the lookupClass) as a lookup class
594 * for method handle creation.
595 * Must be called by from a method in this package,
596 * which in turn is called by a method not in this package.
597 */
598 Lookup(Class<?> lookupClass) {
599 this(lookupClass, ALL_MODES);
600 // make sure we haven't accidentally picked up a privileged class:
601 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
602 }
603
604 private Lookup(Class<?> lookupClass, int allowedModes) {
605 this.lookupClass = lookupClass;
606 this.allowedModes = allowedModes;
607 }
608
609 /**
610 * Creates a lookup on the specified new lookup class.
611 * The resulting object will report the specified
612 * class as its own {@link #lookupClass lookupClass}.
613 * <p>
614 * However, the resulting {@code Lookup} object is guaranteed
615 * to have no more access capabilities than the original.
616 * In particular, access capabilities can be lost as follows:<ul>
617 * <li>If the new lookup class differs from the old one,
618 * protected members will not be accessible by virtue of inheritance.
619 * (Protected members may continue to be accessible because of package sharing.)
620 * <li>If the new lookup class is in a different package
621 * than the old one, protected and default (package) members will not be accessible.
622 * <li>If the new lookup class is not within the same package member
623 * as the old one, private members will not be accessible.
624 * <li>If the new lookup class is not accessible to the old lookup class,
625 * then no members, not even public members, will be accessible.
626 * (In all other cases, public members will continue to be accessible.)
627 * </ul>
628 *
629 * @param requestedLookupClass the desired lookup class for the new lookup object
630 * @return a lookup object which reports the desired lookup class
631 * @throws NullPointerException if the argument is null
632 */
633 public Lookup in(Class<?> requestedLookupClass) {
634 requestedLookupClass.getClass(); // null check
635 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
636 return new Lookup(requestedLookupClass, ALL_MODES);
637 if (requestedLookupClass == this.lookupClass)
638 return this; // keep same capabilities
639 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
640 if ((newModes & PACKAGE) != 0
641 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
642 newModes &= ~(PACKAGE|PRIVATE);
643 }
644 // Allow nestmate lookups to be created without special privilege:
645 if ((newModes & PRIVATE) != 0
646 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
647 newModes &= ~PRIVATE;
648 }
649 if ((newModes & PUBLIC) != 0
650 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
651 // The requested class it not accessible from the lookup class.
652 // No permissions.
653 newModes = 0;
654 }
655 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
656 return new Lookup(requestedLookupClass, newModes);
657 }
658
659 // Make sure outer class is initialized first.
660 static { IMPL_NAMES.getClass(); }
661
662 /** Version of lookup which is trusted minimally.
663 * It can only be used to create method handles to
664 * publicly accessible members.
665 */
666 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
667
668 /** Package-private version of lookup which is trusted. */
669 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
670
671 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
672 String name = lookupClass.getName();
673 if (name.startsWith("java.lang.invoke."))
674 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
675
676 // For caller-sensitive MethodHandles.lookup()
677 // disallow lookup more restricted packages
678 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
679 if (name.startsWith("java.") ||
680 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
681 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
682 }
683 }
684 }
685
686 /**
687 * Displays the name of the class from which lookups are to be made.
688 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
689 * If there are restrictions on the access permitted to this lookup,
690 * this is indicated by adding a suffix to the class name, consisting
691 * of a slash and a keyword. The keyword represents the strongest
692 * allowed access, and is chosen as follows:
693 * <ul>
694 * <li>If no access is allowed, the suffix is "/noaccess".
695 * <li>If only public access is allowed, the suffix is "/public".
696 * <li>If only public and package access are allowed, the suffix is "/package".
697 * <li>If only public, package, and private access are allowed, the suffix is "/private".
698 * </ul>
699 * If none of the above cases apply, it is the case that full
700 * access (public, package, private, and protected) is allowed.
701 * In this case, no suffix is added.
702 * This is true only of an object obtained originally from
703 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
704 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
705 * always have restricted access, and will display a suffix.
706 * <p>
707 * (It may seem strange that protected access should be
708 * stronger than private access. Viewed independently from
709 * package access, protected access is the first to be lost,
710 * because it requires a direct subclass relationship between
711 * caller and callee.)
712 * @see #in
713 */
714 @Override
715 public String toString() {
716 String cname = lookupClass.getName();
717 switch (allowedModes) {
718 case 0: // no privileges
719 return cname + "/noaccess";
720 case PUBLIC:
721 return cname + "/public";
722 case PUBLIC|PACKAGE:
723 return cname + "/package";
724 case ALL_MODES & ~PROTECTED:
725 return cname + "/private";
726 case ALL_MODES:
727 return cname;
728 case TRUSTED:
729 return "/trusted"; // internal only; not exported
730 default: // Should not happen, but it's a bitfield...
731 cname = cname + "/" + Integer.toHexString(allowedModes);
732 assert(false) : cname;
733 return cname;
734 }
735 }
736
737 /**
738 * Produces a method handle for a static method.
739 * The type of the method handle will be that of the method.
740 * (Since static methods do not take receivers, there is no
741 * additional receiver argument inserted into the method handle type,
742 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
743 * The method and all its argument types must be accessible to the lookup object.
744 * <p>
745 * The returned method handle will have
746 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
747 * the method's variable arity modifier bit ({@code 0x0080}) is set.
748 * <p>
749 * If the returned method handle is invoked, the method's class will
750 * be initialized, if it has not already been initialized.
751 * <p><b>Example:</b>
752 * <blockquote><pre>{@code
753 import static java.lang.invoke.MethodHandles.*;
754 import static java.lang.invoke.MethodType.*;
755 ...
756 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
757 "asList", methodType(List.class, Object[].class));
758 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
759 * }</pre></blockquote>
760 * @param refc the class from which the method is accessed
761 * @param name the name of the method
762 * @param type the type of the method
763 * @return the desired method handle
764 * @throws NoSuchMethodException if the method does not exist
765 * @throws IllegalAccessException if access checking fails,
766 * or if the method is not {@code static},
767 * or if the method's variable arity modifier bit
768 * is set and {@code asVarargsCollector} fails
769 * @exception SecurityException if a security manager is present and it
770 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
771 * @throws NullPointerException if any argument is null
772 */
773 public
774 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
775 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
776 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
777 }
778
779 /**
780 * Produces a method handle for a virtual method.
781 * The type of the method handle will be that of the method,
782 * with the receiver type (usually {@code refc}) prepended.
783 * The method and all its argument types must be accessible to the lookup object.
784 * <p>
785 * When called, the handle will treat the first argument as a receiver
786 * and dispatch on the receiver's type to determine which method
787 * implementation to enter.
788 * (The dispatching action is identical with that performed by an
789 * {@code invokevirtual} or {@code invokeinterface} instruction.)
790 * <p>
791 * The first argument will be of type {@code refc} if the lookup
792 * class has full privileges to access the member. Otherwise
793 * the member must be {@code protected} and the first argument
794 * will be restricted in type to the lookup class.
795 * <p>
796 * The returned method handle will have
797 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
798 * the method's variable arity modifier bit ({@code 0x0080}) is set.
799 * <p>
800 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
801 * instructions and method handles produced by {@code findVirtual},
802 * if the class is {@code MethodHandle} and the name string is
803 * {@code invokeExact} or {@code invoke}, the resulting
804 * method handle is equivalent to one produced by
805 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
806 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
807 * with the same {@code type} argument.
808 *
809 * <b>Example:</b>
810 * <blockquote><pre>{@code
811 import static java.lang.invoke.MethodHandles.*;
812 import static java.lang.invoke.MethodType.*;
813 ...
814 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
815 "concat", methodType(String.class, String.class));
816 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
817 "hashCode", methodType(int.class));
818 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
819 "hashCode", methodType(int.class));
820 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
821 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
822 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
823 // interface method:
824 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
825 "subSequence", methodType(CharSequence.class, int.class, int.class));
826 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
827 // constructor "internal method" must be accessed differently:
828 MethodType MT_newString = methodType(void.class); //()V for new String()
829 try { assertEquals("impossible", lookup()
830 .findVirtual(String.class, "<init>", MT_newString));
831 } catch (NoSuchMethodException ex) { } // OK
832 MethodHandle MH_newString = publicLookup()
833 .findConstructor(String.class, MT_newString);
834 assertEquals("", (String) MH_newString.invokeExact());
835 * }</pre></blockquote>
836 *
837 * @param refc the class or interface from which the method is accessed
838 * @param name the name of the method
839 * @param type the type of the method, with the receiver argument omitted
840 * @return the desired method handle
841 * @throws NoSuchMethodException if the method does not exist
842 * @throws IllegalAccessException if access checking fails,
843 * or if the method is {@code static}
844 * or if the method's variable arity modifier bit
845 * is set and {@code asVarargsCollector} fails
846 * @exception SecurityException if a security manager is present and it
847 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
848 * @throws NullPointerException if any argument is null
849 */
850 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
851 if (refc == MethodHandle.class) {
852 MethodHandle mh = findVirtualForMH(name, type);
853 if (mh != null) return mh;
854 }
855 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
856 MemberName method = resolveOrFail(refKind, refc, name, type);
857 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
858 }
859 private MethodHandle findVirtualForMH(String name, MethodType type) {
860 // these names require special lookups because of the implicit MethodType argument
861 if ("invoke".equals(name))
862 return invoker(type);
863 if ("invokeExact".equals(name))
864 return exactInvoker(type);
865 if ("invokeBasic".equals(name))
866 return basicInvoker(type);
867 assert(!MemberName.isMethodHandleInvokeName(name));
868 return null;
869 }
870
871 /**
872 * Produces a method handle which creates an object and initializes it, using
873 * the constructor of the specified type.
874 * The parameter types of the method handle will be those of the constructor,
875 * while the return type will be a reference to the constructor's class.
876 * The constructor and all its argument types must be accessible to the lookup object.
877 * <p>
878 * The requested type must have a return type of {@code void}.
879 * (This is consistent with the JVM's treatment of constructor type descriptors.)
880 * <p>
881 * The returned method handle will have
882 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
883 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
884 * <p>
885 * If the returned method handle is invoked, the constructor's class will
886 * be initialized, if it has not already been initialized.
887 * <p><b>Example:</b>
888 * <blockquote><pre>{@code
889 import static java.lang.invoke.MethodHandles.*;
890 import static java.lang.invoke.MethodType.*;
891 ...
892 MethodHandle MH_newArrayList = publicLookup().findConstructor(
893 ArrayList.class, methodType(void.class, Collection.class));
894 Collection orig = Arrays.asList("x", "y");
895 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
896 assert(orig != copy);
897 assertEquals(orig, copy);
898 // a variable-arity constructor:
899 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
900 ProcessBuilder.class, methodType(void.class, String[].class));
901 ProcessBuilder pb = (ProcessBuilder)
902 MH_newProcessBuilder.invoke("x", "y", "z");
903 assertEquals("[x, y, z]", pb.command().toString());
904 * }</pre></blockquote>
905 * @param refc the class or interface from which the method is accessed
906 * @param type the type of the method, with the receiver argument omitted, and a void return type
907 * @return the desired method handle
908 * @throws NoSuchMethodException if the constructor does not exist
909 * @throws IllegalAccessException if access checking fails
910 * or if the method's variable arity modifier bit
911 * is set and {@code asVarargsCollector} fails
912 * @exception SecurityException if a security manager is present and it
913 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
914 * @throws NullPointerException if any argument is null
915 */
916 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
917 String name = "<init>";
918 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
919 return getDirectConstructor(refc, ctor);
920 }
921
922 /**
923 * Produces an early-bound method handle for a virtual method.
924 * It will bypass checks for overriding methods on the receiver,
925 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
926 * instruction from within the explicitly specified {@code specialCaller}.
927 * The type of the method handle will be that of the method,
928 * with a suitably restricted receiver type prepended.
929 * (The receiver type will be {@code specialCaller} or a subtype.)
930 * The method and all its argument types must be accessible
931 * to the lookup object.
932 * <p>
933 * Before method resolution,
934 * if the explicitly specified caller class is not identical with the
935 * lookup class, or if this lookup object does not have
936 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
937 * privileges, the access fails.
938 * <p>
939 * The returned method handle will have
940 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
941 * the method's variable arity modifier bit ({@code 0x0080}) is set.
942 * <p style="font-size:smaller;">
943 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
944 * even though the {@code invokespecial} instruction can refer to them
945 * in special circumstances. Use {@link #findConstructor findConstructor}
946 * to access instance initialization methods in a safe manner.)</em>
947 * <p><b>Example:</b>
948 * <blockquote><pre>{@code
949 import static java.lang.invoke.MethodHandles.*;
950 import static java.lang.invoke.MethodType.*;
951 ...
952 static class Listie extends ArrayList {
953 public String toString() { return "[wee Listie]"; }
954 static Lookup lookup() { return MethodHandles.lookup(); }
955 }
956 ...
957 // no access to constructor via invokeSpecial:
958 MethodHandle MH_newListie = Listie.lookup()
959 .findConstructor(Listie.class, methodType(void.class));
960 Listie l = (Listie) MH_newListie.invokeExact();
961 try { assertEquals("impossible", Listie.lookup().findSpecial(
962 Listie.class, "<init>", methodType(void.class), Listie.class));
963 } catch (NoSuchMethodException ex) { } // OK
964 // access to super and self methods via invokeSpecial:
965 MethodHandle MH_super = Listie.lookup().findSpecial(
966 ArrayList.class, "toString" , methodType(String.class), Listie.class);
967 MethodHandle MH_this = Listie.lookup().findSpecial(
968 Listie.class, "toString" , methodType(String.class), Listie.class);
969 MethodHandle MH_duper = Listie.lookup().findSpecial(
970 Object.class, "toString" , methodType(String.class), Listie.class);
971 assertEquals("[]", (String) MH_super.invokeExact(l));
972 assertEquals(""+l, (String) MH_this.invokeExact(l));
973 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
974 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
975 String.class, "toString", methodType(String.class), Listie.class));
976 } catch (IllegalAccessException ex) { } // OK
977 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
978 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
979 * }</pre></blockquote>
980 *
981 * @param refc the class or interface from which the method is accessed
982 * @param name the name of the method (which must not be "<init>")
983 * @param type the type of the method, with the receiver argument omitted
984 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
985 * @return the desired method handle
986 * @throws NoSuchMethodException if the method does not exist
987 * @throws IllegalAccessException if access checking fails
988 * or if the method's variable arity modifier bit
989 * is set and {@code asVarargsCollector} fails
990 * @exception SecurityException if a security manager is present and it
991 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
992 * @throws NullPointerException if any argument is null
993 */
994 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
995 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
996 checkSpecialCaller(specialCaller);
997 Lookup specialLookup = this.in(specialCaller);
998 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
999 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1000 }
1001
1002 /**
1003 * Produces a method handle giving read access to a non-static field.
1004 * The type of the method handle will have a return type of the field's
1005 * value type.
1006 * The method handle's single argument will be the instance containing
1007 * the field.
1008 * Access checking is performed immediately on behalf of the lookup class.
1009 * @param refc the class or interface from which the method is accessed
1010 * @param name the field's name
1011 * @param type the field's type
1012 * @return a method handle which can load values from the field
1013 * @throws NoSuchFieldException if the field does not exist
1014 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1015 * @exception SecurityException if a security manager is present and it
1016 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1017 * @throws NullPointerException if any argument is null
1018 */
1019 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1020 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1021 return getDirectField(REF_getField, refc, field);
1022 }
1023
1024 /**
1025 * Produces a method handle giving write access to a non-static field.
1026 * The type of the method handle will have a void return type.
1027 * The method handle will take two arguments, the instance containing
1028 * the field, and the value to be stored.
1029 * The second argument will be of the field's value type.
1030 * Access checking is performed immediately on behalf of the lookup class.
1031 * @param refc the class or interface from which the method is accessed
1032 * @param name the field's name
1033 * @param type the field's type
1034 * @return a method handle which can store values into the field
1035 * @throws NoSuchFieldException if the field does not exist
1036 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1037 * @exception SecurityException if a security manager is present and it
1038 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1039 * @throws NullPointerException if any argument is null
1040 */
1041 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1042 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1043 return getDirectField(REF_putField, refc, field);
1044 }
1045
1046 /**
1047 * Produces a method handle giving read access to a static field.
1048 * The type of the method handle will have a return type of the field's
1049 * value type.
1050 * The method handle will take no arguments.
1051 * Access checking is performed immediately on behalf of the lookup class.
1052 * <p>
1053 * If the returned method handle is invoked, the field's class will
1054 * be initialized, if it has not already been initialized.
1055 * @param refc the class or interface from which the method is accessed
1056 * @param name the field's name
1057 * @param type the field's type
1058 * @return a method handle which can load values from the field
1059 * @throws NoSuchFieldException if the field does not exist
1060 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1061 * @exception SecurityException if a security manager is present and it
1062 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1063 * @throws NullPointerException if any argument is null
1064 */
1065 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1066 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1067 return getDirectField(REF_getStatic, refc, field);
1068 }
1069
1070 /**
1071 * Produces a method handle giving write access to a static field.
1072 * The type of the method handle will have a void return type.
1073 * The method handle will take a single
1074 * argument, of the field's value type, the value to be stored.
1075 * Access checking is performed immediately on behalf of the lookup class.
1076 * <p>
1077 * If the returned method handle is invoked, the field's class will
1078 * be initialized, if it has not already been initialized.
1079 * @param refc the class or interface from which the method is accessed
1080 * @param name the field's name
1081 * @param type the field's type
1082 * @return a method handle which can store values into the field
1083 * @throws NoSuchFieldException if the field does not exist
1084 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1085 * @exception SecurityException if a security manager is present and it
1086 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1087 * @throws NullPointerException if any argument is null
1088 */
1089 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1090 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1091 return getDirectField(REF_putStatic, refc, field);
1092 }
1093
1094 /**
1095 * Produces an early-bound method handle for a non-static method.
1096 * The receiver must have a supertype {@code defc} in which a method
1097 * of the given name and type is accessible to the lookup class.
1098 * The method and all its argument types must be accessible to the lookup object.
1099 * The type of the method handle will be that of the method,
1100 * without any insertion of an additional receiver parameter.
1101 * The given receiver will be bound into the method handle,
1102 * so that every call to the method handle will invoke the
1103 * requested method on the given receiver.
1104 * <p>
1105 * The returned method handle will have
1106 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1107 * the method's variable arity modifier bit ({@code 0x0080}) is set
1108 * <em>and</em> the trailing array argument is not the only argument.
1109 * (If the trailing array argument is the only argument,
1110 * the given receiver value will be bound to it.)
1111 * <p>
1112 * This is equivalent to the following code:
1113 * <blockquote><pre>{@code
1114 import static java.lang.invoke.MethodHandles.*;
1115 import static java.lang.invoke.MethodType.*;
1116 ...
1117 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1118 MethodHandle mh1 = mh0.bindTo(receiver);
1119 MethodType mt1 = mh1.type();
1120 if (mh0.isVarargsCollector())
1121 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1122 return mh1;
1123 * }</pre></blockquote>
1124 * where {@code defc} is either {@code receiver.getClass()} or a super
1125 * type of that class, in which the requested method is accessible
1126 * to the lookup class.
1127 * (Note that {@code bindTo} does not preserve variable arity.)
1128 * @param receiver the object from which the method is accessed
1129 * @param name the name of the method
1130 * @param type the type of the method, with the receiver argument omitted
1131 * @return the desired method handle
1132 * @throws NoSuchMethodException if the method does not exist
1133 * @throws IllegalAccessException if access checking fails
1134 * or if the method's variable arity modifier bit
1135 * is set and {@code asVarargsCollector} fails
1136 * @exception SecurityException if a security manager is present and it
1137 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1138 * @throws NullPointerException if any argument is null
1139 * @see MethodHandle#bindTo
1140 * @see #findVirtual
1141 */
1142 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1143 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1144 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1145 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1146 return mh.bindReceiver(receiver).setVarargs(method);
1147 }
1148
1149 /**
1150 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1151 * to <i>m</i>, if the lookup class has permission.
1152 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1153 * If <i>m</i> is virtual, overriding is respected on every call.
1154 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1155 * The type of the method handle will be that of the method,
1156 * with the receiver type prepended (but only if it is non-static).
1157 * If the method's {@code accessible} flag is not set,
1158 * access checking is performed immediately on behalf of the lookup class.
1159 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1160 * <p>
1161 * The returned method handle will have
1162 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1163 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1164 * <p>
1165 * If <i>m</i> is static, and
1166 * if the returned method handle is invoked, the method's class will
1167 * be initialized, if it has not already been initialized.
1168 * @param m the reflected method
1169 * @return a method handle which can invoke the reflected method
1170 * @throws IllegalAccessException if access checking fails
1171 * or if the method's variable arity modifier bit
1172 * is set and {@code asVarargsCollector} fails
1173 * @throws NullPointerException if the argument is null
1174 */
1175 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1176 if (m.getDeclaringClass() == MethodHandle.class) {
1177 MethodHandle mh = unreflectForMH(m);
1178 if (mh != null) return mh;
1179 }
1180 MemberName method = new MemberName(m);
1181 byte refKind = method.getReferenceKind();
1182 if (refKind == REF_invokeSpecial)
1183 refKind = REF_invokeVirtual;
1184 assert(method.isMethod());
1185 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1186 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1187 }
1188 private MethodHandle unreflectForMH(Method m) {
1189 // these names require special lookups because they throw UnsupportedOperationException
1190 if (MemberName.isMethodHandleInvokeName(m.getName()))
1191 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1192 return null;
1193 }
1194
1195 /**
1196 * Produces a method handle for a reflected method.
1197 * It will bypass checks for overriding methods on the receiver,
1198 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1199 * instruction from within the explicitly specified {@code specialCaller}.
1200 * The type of the method handle will be that of the method,
1201 * with a suitably restricted receiver type prepended.
1202 * (The receiver type will be {@code specialCaller} or a subtype.)
1203 * If the method's {@code accessible} flag is not set,
1204 * access checking is performed immediately on behalf of the lookup class,
1205 * as if {@code invokespecial} instruction were being linked.
1206 * <p>
1207 * Before method resolution,
1208 * if the explicitly specified caller class is not identical with the
1209 * lookup class, or if this lookup object does not have
1210 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1211 * privileges, the access fails.
1212 * <p>
1213 * The returned method handle will have
1214 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1215 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1216 * @param m the reflected method
1217 * @param specialCaller the class nominally calling the method
1218 * @return a method handle which can invoke the reflected method
1219 * @throws IllegalAccessException if access checking fails
1220 * or if the method's variable arity modifier bit
1221 * is set and {@code asVarargsCollector} fails
1222 * @throws NullPointerException if any argument is null
1223 */
1224 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1225 checkSpecialCaller(specialCaller);
1226 Lookup specialLookup = this.in(specialCaller);
1227 MemberName method = new MemberName(m, true);
1228 assert(method.isMethod());
1229 // ignore m.isAccessible: this is a new kind of access
1230 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1231 }
1232
1233 /**
1234 * Produces a method handle for a reflected constructor.
1235 * The type of the method handle will be that of the constructor,
1236 * with the return type changed to the declaring class.
1237 * The method handle will perform a {@code newInstance} operation,
1238 * creating a new instance of the constructor's class on the
1239 * arguments passed to the method handle.
1240 * <p>
1241 * If the constructor's {@code accessible} flag is not set,
1242 * access checking is performed immediately on behalf of the lookup class.
1243 * <p>
1244 * The returned method handle will have
1245 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1246 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1247 * <p>
1248 * If the returned method handle is invoked, the constructor's class will
1249 * be initialized, if it has not already been initialized.
1250 * @param c the reflected constructor
1251 * @return a method handle which can invoke the reflected constructor
1252 * @throws IllegalAccessException if access checking fails
1253 * or if the method's variable arity modifier bit
1254 * is set and {@code asVarargsCollector} fails
1255 * @throws NullPointerException if the argument is null
1256 */
1257 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1258 MemberName ctor = new MemberName(c);
1259 assert(ctor.isConstructor());
1260 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1261 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1262 }
1263
1264 /**
1265 * Produces a method handle giving read access to a reflected field.
1266 * The type of the method handle will have a return type of the field's
1267 * value type.
1268 * If the field is static, the method handle will take no arguments.
1269 * Otherwise, its single argument will be the instance containing
1270 * the field.
1271 * If the field's {@code accessible} flag is not set,
1272 * access checking is performed immediately on behalf of the lookup class.
1273 * <p>
1274 * If the field is static, and
1275 * if the returned method handle is invoked, the field's class will
1276 * be initialized, if it has not already been initialized.
1277 * @param f the reflected field
1278 * @return a method handle which can load values from the reflected field
1279 * @throws IllegalAccessException if access checking fails
1280 * @throws NullPointerException if the argument is null
1281 */
1282 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1283 return unreflectField(f, false);
1284 }
1285 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1286 MemberName field = new MemberName(f, isSetter);
1287 assert(isSetter
1288 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1289 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1290 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1291 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1292 }
1293
1294 /**
1295 * Produces a method handle giving write access to a reflected field.
1296 * The type of the method handle will have a void return type.
1297 * If the field is static, the method handle will take a single
1298 * argument, of the field's value type, the value to be stored.
1299 * Otherwise, the two arguments will be the instance containing
1300 * the field, and the value to be stored.
1301 * If the field's {@code accessible} flag is not set,
1302 * access checking is performed immediately on behalf of the lookup class.
1303 * <p>
1304 * If the field is static, and
1305 * if the returned method handle is invoked, the field's class will
1306 * be initialized, if it has not already been initialized.
1307 * @param f the reflected field
1308 * @return a method handle which can store values into the reflected field
1309 * @throws IllegalAccessException if access checking fails
1310 * @throws NullPointerException if the argument is null
1311 */
1312 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1313 return unreflectField(f, true);
1314 }
1315
1316 /**
1317 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1318 * created by this lookup object or a similar one.
1319 * Security and access checks are performed to ensure that this lookup object
1320 * is capable of reproducing the target method handle.
1321 * This means that the cracking may fail if target is a direct method handle
1322 * but was created by an unrelated lookup object.
1323 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1324 * and was created by a lookup object for a different class.
1325 * @param target a direct method handle to crack into symbolic reference components
1326 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1327 * @exception SecurityException if a security manager is present and it
1328 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1329 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1330 * @exception NullPointerException if the target is {@code null}
1331 * @see MethodHandleInfo
1332 * @since 1.8
1333 */
1334 public MethodHandleInfo revealDirect(MethodHandle target) {
1335 MemberName member = target.internalMemberName();
1336 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1337 throw newIllegalArgumentException("not a direct method handle");
1338 Class<?> defc = member.getDeclaringClass();
1339 byte refKind = member.getReferenceKind();
1340 assert(MethodHandleNatives.refKindIsValid(refKind));
1341 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1342 // Devirtualized method invocation is usually formally virtual.
1343 // To avoid creating extra MemberName objects for this common case,
1344 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1345 refKind = REF_invokeVirtual;
1346 if (refKind == REF_invokeVirtual && defc.isInterface())
1347 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1348 refKind = REF_invokeInterface;
1349 // Check SM permissions and member access before cracking.
1350 try {
1351 checkAccess(refKind, defc, member);
1352 checkSecurityManager(defc, member);
1353 } catch (IllegalAccessException ex) {
1354 throw new IllegalArgumentException(ex);
1355 }
1356 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1357 Class<?> callerClass = target.internalCallerClass();
1358 if (!hasPrivateAccess() || callerClass != lookupClass())
1359 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1360 }
1361 // Produce the handle to the results.
1362 return new InfoFromMemberName(this, member, refKind);
1363 }
1364
1365 /// Helper methods, all package-private.
1366
1367 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1368 checkSymbolicClass(refc); // do this before attempting to resolve
1369 name.getClass(); // NPE
1370 type.getClass(); // NPE
1371 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1372 NoSuchFieldException.class);
1373 }
1374
1375 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1376 checkSymbolicClass(refc); // do this before attempting to resolve
1377 name.getClass(); // NPE
1378 type.getClass(); // NPE
1379 checkMethodName(refKind, name); // NPE check on name
1380 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1381 NoSuchMethodException.class);
1382 }
1383
1384 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1385 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1386 member.getName().getClass(); // NPE
1387 member.getType().getClass(); // NPE
1388 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1389 ReflectiveOperationException.class);
1390 }
1391
1392 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1393 refc.getClass(); // NPE
1394 Class<?> caller = lookupClassOrNull();
1395 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1396 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1397 }
1398
1399 /** Check name for an illegal leading "<" character. */
1400 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1401 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1402 throw new NoSuchMethodException("illegal method name: "+name);
1403 }
1404
1405
1406 /**
1407 * Find my trustable caller class if m is a caller sensitive method.
1408 * If this lookup object has private access, then the caller class is the lookupClass.
1409 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1410 */
1411 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1412 Class<?> callerClass = null;
1413 if (MethodHandleNatives.isCallerSensitive(m)) {
1414 // Only lookups with private access are allowed to resolve caller-sensitive methods
1415 if (hasPrivateAccess()) {
1416 callerClass = lookupClass;
1417 } else {
1418 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1419 }
1420 }
1421 return callerClass;
1422 }
1423
1424 private boolean hasPrivateAccess() {
1425 return (allowedModes & PRIVATE) != 0;
1426 }
1427
1428 /**
1429 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1430 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1431 * If this lookup object has private access, then the caller class is the lookupClass.
1432 */
1433 void checkSecurityManager(Class<?> refc, MemberName m) {
1434 SecurityManager smgr = System.getSecurityManager();
1435 if (smgr == null) return;
1436 if (allowedModes == TRUSTED) return;
1437
1438 // Step 1:
1439 boolean fullPowerLookup = hasPrivateAccess();
1440 if (!fullPowerLookup ||
1441 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1442 ReflectUtil.checkPackageAccess(refc);
1443 }
1444
1445 // Step 2:
1446 if (m.isPublic()) return;
1447 if (!fullPowerLookup) {
1448 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1449 }
1450
1451 // Step 3:
1452 Class<?> defc = m.getDeclaringClass();
1453 if (!fullPowerLookup && defc != refc) {
1454 ReflectUtil.checkPackageAccess(defc);
1455 }
1456 }
1457
1458 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1459 boolean wantStatic = (refKind == REF_invokeStatic);
1460 String message;
1461 if (m.isConstructor())
1462 message = "expected a method, not a constructor";
1463 else if (!m.isMethod())
1464 message = "expected a method";
1465 else if (wantStatic != m.isStatic())
1466 message = wantStatic ? "expected a static method" : "expected a non-static method";
1467 else
1468 { checkAccess(refKind, refc, m); return; }
1469 throw m.makeAccessException(message, this);
1470 }
1471
1472 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1473 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1474 String message;
1475 if (wantStatic != m.isStatic())
1476 message = wantStatic ? "expected a static field" : "expected a non-static field";
1477 else
1478 { checkAccess(refKind, refc, m); return; }
1479 throw m.makeAccessException(message, this);
1480 }
1481
1482 /** Check public/protected/private bits on the symbolic reference class and its member. */
1483 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1484 assert(m.referenceKindIsConsistentWith(refKind) &&
1485 MethodHandleNatives.refKindIsValid(refKind) &&
1486 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1487 int allowedModes = this.allowedModes;
1488 if (allowedModes == TRUSTED) return;
1489 int mods = m.getModifiers();
1490 if (Modifier.isProtected(mods) &&
1491 refKind == REF_invokeVirtual &&
1492 m.getDeclaringClass() == Object.class &&
1493 m.getName().equals("clone") &&
1494 refc.isArray()) {
1495 // The JVM does this hack also.
1496 // (See ClassVerifier::verify_invoke_instructions
1497 // and LinkResolver::check_method_accessability.)
1498 // Because the JVM does not allow separate methods on array types,
1499 // there is no separate method for int[].clone.
1500 // All arrays simply inherit Object.clone.
1501 // But for access checking logic, we make Object.clone
1502 // (normally protected) appear to be public.
1503 // Later on, when the DirectMethodHandle is created,
1504 // its leading argument will be restricted to the
1505 // requested array type.
1506 // N.B. The return type is not adjusted, because
1507 // that is *not* the bytecode behavior.
1508 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1509 }
1510 if (Modifier.isFinal(mods) &&
1511 MethodHandleNatives.refKindIsSetter(refKind))
1512 throw m.makeAccessException("unexpected set of a final field", this);
1513 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1514 return; // common case
1515 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1516 if ((requestedModes & allowedModes) != 0) {
1517 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1518 mods, lookupClass(), allowedModes))
1519 return;
1520 } else {
1521 // Protected members can also be checked as if they were package-private.
1522 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1523 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1524 return;
1525 }
1526 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1527 }
1528
1529 String accessFailedMessage(Class<?> refc, MemberName m) {
1530 Class<?> defc = m.getDeclaringClass();
1531 int mods = m.getModifiers();
1532 // check the class first:
1533 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1534 (defc == refc ||
1535 Modifier.isPublic(refc.getModifiers())));
1536 if (!classOK && (allowedModes & PACKAGE) != 0) {
1537 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1538 (defc == refc ||
1539 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1540 }
1541 if (!classOK)
1542 return "class is not public";
1543 if (Modifier.isPublic(mods))
1544 return "access to public member failed"; // (how?)
1545 if (Modifier.isPrivate(mods))
1546 return "member is private";
1547 if (Modifier.isProtected(mods))
1548 return "member is protected";
1549 return "member is private to package";
1550 }
1551
1552 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1553
1554 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1555 int allowedModes = this.allowedModes;
1556 if (allowedModes == TRUSTED) return;
1557 if (!hasPrivateAccess()
1558 || (specialCaller != lookupClass()
1559 && !(ALLOW_NESTMATE_ACCESS &&
1560 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1561 throw new MemberName(specialCaller).
1562 makeAccessException("no private access for invokespecial", this);
1563 }
1564
1565 private boolean restrictProtectedReceiver(MemberName method) {
1566 // The accessing class only has the right to use a protected member
1567 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1568 if (!method.isProtected() || method.isStatic()
1569 || allowedModes == TRUSTED
1570 || method.getDeclaringClass() == lookupClass()
1571 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1572 || (ALLOW_NESTMATE_ACCESS &&
1573 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1574 return false;
1575 return true;
1576 }
1577 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1578 assert(!method.isStatic());
1579 // receiver type of mh is too wide; narrow to caller
1580 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1581 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1582 }
1583 MethodType rawType = mh.type();
1584 if (rawType.parameterType(0) == caller) return mh;
1585 MethodType narrowType = rawType.changeParameterType(0, caller);
1586 return mh.viewAsType(narrowType);
1587 }
1588
1589 /** Check access and get the requested method. */
1590 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1591 final boolean doRestrict = true;
1592 final boolean checkSecurity = true;
1593 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1594 }
1595 /** Check access and get the requested method, eliding receiver narrowing rules. */
1596 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1597 final boolean doRestrict = false;
1598 final boolean checkSecurity = true;
1599 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1600 }
1601 /** Check access and get the requested method, eliding security manager checks. */
1602 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1603 final boolean doRestrict = true;
1604 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1605 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1606 }
1607 /** Common code for all methods; do not call directly except from immediately above. */
1608 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1609 boolean checkSecurity,
1610 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1611 checkMethod(refKind, refc, method);
1612 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1613 if (checkSecurity)
1614 checkSecurityManager(refc, method);
1615 assert(!method.isMethodHandleInvoke());
1616
1617 if (refKind == REF_invokeSpecial &&
1618 refc != lookupClass() &&
1619 !refc.isInterface() &&
1620 refc != lookupClass().getSuperclass() &&
1621 refc.isAssignableFrom(lookupClass())) {
1622 assert(!method.getName().equals("<init>")); // not this code path
1623 // Per JVMS 6.5, desc. of invokespecial instruction:
1624 // If the method is in a superclass of the LC,
1625 // and if our original search was above LC.super,
1626 // repeat the search (symbolic lookup) from LC.super
1627 // and continue with the direct superclass of that class,
1628 // and so forth, until a match is found or no further superclasses exist.
1629 // FIXME: MemberName.resolve should handle this instead.
1630 Class<?> refcAsSuper = lookupClass();
1631 MemberName m2;
1632 do {
1633 refcAsSuper = refcAsSuper.getSuperclass();
1634 m2 = new MemberName(refcAsSuper,
1635 method.getName(),
1636 method.getMethodType(),
1637 REF_invokeSpecial);
1638 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1639 } while (m2 == null && // no method is found yet
1640 refc != refcAsSuper); // search up to refc
1641 if (m2 == null) throw new InternalError(method.toString());
1642 method = m2;
1643 refc = refcAsSuper;
1644 // redo basic checks
1645 checkMethod(refKind, refc, method);
1646 }
1647
1648 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1649 mh = maybeBindCaller(method, mh, callerClass);
1650 mh = mh.setVarargs(method);
1651 // Optionally narrow the receiver argument to refc using restrictReceiver.
1652 if (doRestrict &&
1653 (refKind == REF_invokeSpecial ||
1654 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1655 restrictProtectedReceiver(method))))
1656 mh = restrictReceiver(method, mh, lookupClass());
1657 return mh;
1658 }
1659 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1660 Class<?> callerClass)
1661 throws IllegalAccessException {
1662 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1663 return mh;
1664 Class<?> hostClass = lookupClass;
1665 if (!hasPrivateAccess()) // caller must have private access
1666 hostClass = callerClass; // callerClass came from a security manager style stack walk
1667 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1668 // Note: caller will apply varargs after this step happens.
1669 return cbmh;
1670 }
1671 /** Check access and get the requested field. */
1672 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1673 final boolean checkSecurity = true;
1674 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1675 }
1676 /** Check access and get the requested field, eliding security manager checks. */
1677 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1678 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1679 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1680 }
1681 /** Common code for all fields; do not call directly except from immediately above. */
1682 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1683 boolean checkSecurity) throws IllegalAccessException {
1684 checkField(refKind, refc, field);
1685 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1686 if (checkSecurity)
1687 checkSecurityManager(refc, field);
1688 MethodHandle mh = DirectMethodHandle.make(refc, field);
1689 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1690 restrictProtectedReceiver(field));
1691 if (doRestrict)
1692 mh = restrictReceiver(field, mh, lookupClass());
1693 return mh;
1694 }
1695 /** Check access and get the requested constructor. */
1696 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1697 final boolean checkSecurity = true;
1698 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1699 }
1700 /** Check access and get the requested constructor, eliding security manager checks. */
1701 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1702 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1703 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1704 }
1705 /** Common code for all constructors; do not call directly except from immediately above. */
1706 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1707 boolean checkSecurity) throws IllegalAccessException {
1708 assert(ctor.isConstructor());
1709 checkAccess(REF_newInvokeSpecial, refc, ctor);
1710 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1711 if (checkSecurity)
1712 checkSecurityManager(refc, ctor);
1713 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1714 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1715 }
1716
1717 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1718 */
1719 /*non-public*/
1720 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1721 if (!(type instanceof Class || type instanceof MethodType))
1722 throw new InternalError("unresolved MemberName");
1723 MemberName member = new MemberName(refKind, defc, name, type);
1724 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1725 if (mh != null) {
1726 checkSymbolicClass(defc);
1727 return mh;
1728 }
1729 // Treat MethodHandle.invoke and invokeExact specially.
1730 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1731 mh = findVirtualForMH(member.getName(), member.getMethodType());
1732 if (mh != null) {
1733 return mh;
1734 }
1735 }
1736 MemberName resolved = resolveOrFail(refKind, member);
1737 mh = getDirectMethodForConstant(refKind, defc, resolved);
1738 if (mh instanceof DirectMethodHandle
1739 && canBeCached(refKind, defc, resolved)) {
1740 MemberName key = mh.internalMemberName();
1741 if (key != null) {
1742 key = key.asNormalOriginal();
1743 }
1744 if (member.equals(key)) { // better safe than sorry
1745 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1746 }
1747 }
1748 return mh;
1749 }
1750 private
1751 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1752 if (refKind == REF_invokeSpecial) {
1753 return false;
1754 }
1755 if (!Modifier.isPublic(defc.getModifiers()) ||
1756 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1757 !member.isPublic() ||
1758 member.isCallerSensitive()) {
1759 return false;
1760 }
1761 ClassLoader loader = defc.getClassLoader();
1762 if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1763 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1764 boolean found = false;
1765 while (sysl != null) {
1766 if (loader == sysl) { found = true; break; }
1767 sysl = sysl.getParent();
1768 }
1769 if (!found) {
1770 return false;
1771 }
1772 }
1773 try {
1774 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1775 new MemberName(refKind, defc, member.getName(), member.getType()));
1776 checkSecurityManager(defc, resolved2);
1777 } catch (ReflectiveOperationException | SecurityException ex) {
1778 return false;
1779 }
1780 return true;
1781 }
1782 private
1783 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1784 throws ReflectiveOperationException {
1785 if (MethodHandleNatives.refKindIsField(refKind)) {
1786 return getDirectFieldNoSecurityManager(refKind, defc, member);
1787 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1788 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1789 } else if (refKind == REF_newInvokeSpecial) {
1790 return getDirectConstructorNoSecurityManager(defc, member);
1791 }
1792 // oops
1793 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1794 }
1795
1796 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1797 }
1798
1799 /**
1800 * Produces a method handle giving read access to elements of an array.
1801 * The type of the method handle will have a return type of the array's
1802 * element type. Its first argument will be the array type,
1803 * and the second will be {@code int}.
1804 * @param arrayClass an array type
1805 * @return a method handle which can load values from the given array type
1806 * @throws NullPointerException if the argument is null
1807 * @throws IllegalArgumentException if arrayClass is not an array type
1808 */
1809 public static
1810 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1811 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1812 }
1813
1814 /**
1815 * Produces a method handle giving write access to elements of an array.
1816 * The type of the method handle will have a void return type.
1817 * Its last argument will be the array's element type.
1818 * The first and second arguments will be the array type and int.
1819 * @param arrayClass the class of an array
1820 * @return a method handle which can store values into the array type
1821 * @throws NullPointerException if the argument is null
1822 * @throws IllegalArgumentException if arrayClass is not an array type
1823 */
1824 public static
1825 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1826 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1827 }
1828
1829 /// method handle invocation (reflective style)
1830
1831 /**
1832 * Produces a method handle which will invoke any method handle of the
1833 * given {@code type}, with a given number of trailing arguments replaced by
1834 * a single trailing {@code Object[]} array.
1835 * The resulting invoker will be a method handle with the following
1836 * arguments:
1837 * <ul>
1838 * <li>a single {@code MethodHandle} target
1839 * <li>zero or more leading values (counted by {@code leadingArgCount})
1840 * <li>an {@code Object[]} array containing trailing arguments
1841 * </ul>
1842 * <p>
1843 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1844 * the indicated {@code type}.
1845 * That is, if the target is exactly of the given {@code type}, it will behave
1846 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1847 * is used to convert the target to the required {@code type}.
1848 * <p>
1849 * The type of the returned invoker will not be the given {@code type}, but rather
1850 * will have all parameters except the first {@code leadingArgCount}
1851 * replaced by a single array of type {@code Object[]}, which will be
1852 * the final parameter.
1853 * <p>
1854 * Before invoking its target, the invoker will spread the final array, apply
1855 * reference casts as necessary, and unbox and widen primitive arguments.
1856 * If, when the invoker is called, the supplied array argument does
1857 * not have the correct number of elements, the invoker will throw
1858 * an {@link IllegalArgumentException} instead of invoking the target.
1859 * <p>
1860 * This method is equivalent to the following code (though it may be more efficient):
1861 * <blockquote><pre>{@code
1862 MethodHandle invoker = MethodHandles.invoker(type);
1863 int spreadArgCount = type.parameterCount() - leadingArgCount;
1864 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1865 return invoker;
1866 * }</pre></blockquote>
1867 * This method throws no reflective or security exceptions.
1868 * @param type the desired target type
1869 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1870 * @return a method handle suitable for invoking any method handle of the given type
1871 * @throws NullPointerException if {@code type} is null
1872 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1873 * the range from 0 to {@code type.parameterCount()} inclusive,
1874 * or if the resulting method handle's type would have
1875 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1876 */
1877 static public
1878 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1879 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1880 throw new IllegalArgumentException("bad argument count "+leadingArgCount);
1881 return type.invokers().spreadInvoker(leadingArgCount);
1882 }
1883
1884 /**
1885 * Produces a special <em>invoker method handle</em> which can be used to
1886 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1887 * The resulting invoker will have a type which is
1888 * exactly equal to the desired type, except that it will accept
1889 * an additional leading argument of type {@code MethodHandle}.
1890 * <p>
1891 * This method is equivalent to the following code (though it may be more efficient):
1892 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1893 *
1894 * <p style="font-size:smaller;">
1895 * <em>Discussion:</em>
1896 * Invoker method handles can be useful when working with variable method handles
1897 * of unknown types.
1898 * For example, to emulate an {@code invokeExact} call to a variable method
1899 * handle {@code M}, extract its type {@code T},
1900 * look up the invoker method {@code X} for {@code T},
1901 * and call the invoker method, as {@code X.invoke(T, A...)}.
1902 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1903 * is unknown.)
1904 * If spreading, collecting, or other argument transformations are required,
1905 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1906 * method handle values, as long as they are compatible with the type of {@code X}.
1907 * <p style="font-size:smaller;">
1908 * <em>(Note: The invoker method is not available via the Core Reflection API.
1909 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1910 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1911 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1912 * <p>
1913 * This method throws no reflective or security exceptions.
1914 * @param type the desired target type
1915 * @return a method handle suitable for invoking any method handle of the given type
1916 * @throws IllegalArgumentException if the resulting method handle's type would have
1917 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1918 */
1919 static public
1920 MethodHandle exactInvoker(MethodType type) {
1921 return type.invokers().exactInvoker();
1922 }
1923
1924 /**
1925 * Produces a special <em>invoker method handle</em> which can be used to
1926 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1927 * The resulting invoker will have a type which is
1928 * exactly equal to the desired type, except that it will accept
1929 * an additional leading argument of type {@code MethodHandle}.
1930 * <p>
1931 * Before invoking its target, if the target differs from the expected type,
1932 * the invoker will apply reference casts as
1933 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1934 * Similarly, the return value will be converted as necessary.
1935 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1936 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1937 * <p>
1938 * This method is equivalent to the following code (though it may be more efficient):
1939 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1940 * <p style="font-size:smaller;">
1941 * <em>Discussion:</em>
1942 * A {@linkplain MethodType#genericMethodType general method type} is one which
1943 * mentions only {@code Object} arguments and return values.
1944 * An invoker for such a type is capable of calling any method handle
1945 * of the same arity as the general type.
1946 * <p style="font-size:smaller;">
1947 * <em>(Note: The invoker method is not available via the Core Reflection API.
1948 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1949 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1950 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1951 * <p>
1952 * This method throws no reflective or security exceptions.
1953 * @param type the desired target type
1954 * @return a method handle suitable for invoking any method handle convertible to the given type
1955 * @throws IllegalArgumentException if the resulting method handle's type would have
1956 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1957 */
1958 static public
1959 MethodHandle invoker(MethodType type) {
1960 return type.invokers().generalInvoker();
1961 }
1962
1963 static /*non-public*/
1964 MethodHandle basicInvoker(MethodType type) {
1965 return type.invokers().basicInvoker();
1966 }
1967
1968 /// method handle modification (creation from other method handles)
1969
1970 /**
1971 * Produces a method handle which adapts the type of the
1972 * given method handle to a new type by pairwise argument and return type conversion.
1973 * The original type and new type must have the same number of arguments.
1974 * The resulting method handle is guaranteed to report a type
1975 * which is equal to the desired new type.
1976 * <p>
1977 * If the original type and new type are equal, returns target.
1978 * <p>
1979 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1980 * and some additional conversions are also applied if those conversions fail.
1981 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1982 * if possible, before or instead of any conversions done by {@code asType}:
1983 * <ul>
1984 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1985 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1986 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1987 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1988 * the boolean is converted to a byte value, 1 for true, 0 for false.
1989 * (This treatment follows the usage of the bytecode verifier.)
1990 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1991 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1992 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1993 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1994 * then a Java casting conversion (JLS 5.5) is applied.
1995 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
1996 * widening and/or narrowing.)
1997 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1998 * conversion will be applied at runtime, possibly followed
1999 * by a Java casting conversion (JLS 5.5) on the primitive value,
2000 * possibly followed by a conversion from byte to boolean by testing
2001 * the low-order bit.
2002 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2003 * and if the reference is null at runtime, a zero value is introduced.
2004 * </ul>
2005 * @param target the method handle to invoke after arguments are retyped
2006 * @param newType the expected type of the new method handle
2007 * @return a method handle which delegates to the target after performing
2008 * any necessary argument conversions, and arranges for any
2009 * necessary return value conversions
2010 * @throws NullPointerException if either argument is null
2011 * @throws WrongMethodTypeException if the conversion cannot be made
2012 * @see MethodHandle#asType
2013 */
2014 public static
2015 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2016 if (!target.type().isCastableTo(newType)) {
2017 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
2018 }
2019 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
2020 }
2021
2022 /**
2023 * Produces a method handle which adapts the calling sequence of the
2024 * given method handle to a new type, by reordering the arguments.
2025 * The resulting method handle is guaranteed to report a type
2026 * which is equal to the desired new type.
2027 * <p>
2028 * The given array controls the reordering.
2029 * Call {@code #I} the number of incoming parameters (the value
2030 * {@code newType.parameterCount()}, and call {@code #O} the number
2031 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2032 * Then the length of the reordering array must be {@code #O},
2033 * and each element must be a non-negative number less than {@code #I}.
2034 * For every {@code N} less than {@code #O}, the {@code N}-th
2035 * outgoing argument will be taken from the {@code I}-th incoming
2036 * argument, where {@code I} is {@code reorder[N]}.
2037 * <p>
2038 * No argument or return value conversions are applied.
2039 * The type of each incoming argument, as determined by {@code newType},
2040 * must be identical to the type of the corresponding outgoing parameter
2041 * or parameters in the target method handle.
2042 * The return type of {@code newType} must be identical to the return
2043 * type of the original target.
2044 * <p>
2045 * The reordering array need not specify an actual permutation.
2046 * An incoming argument will be duplicated if its index appears
2047 * more than once in the array, and an incoming argument will be dropped
2048 * if its index does not appear in the array.
2049 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2050 * incoming arguments which are not mentioned in the reordering array
2051 * are may be any type, as determined only by {@code newType}.
2052 * <blockquote><pre>{@code
2053 import static java.lang.invoke.MethodHandles.*;
2054 import static java.lang.invoke.MethodType.*;
2055 ...
2056 MethodType intfn1 = methodType(int.class, int.class);
2057 MethodType intfn2 = methodType(int.class, int.class, int.class);
2058 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2059 assert(sub.type().equals(intfn2));
2060 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2061 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2062 assert((int)rsub.invokeExact(1, 100) == 99);
2063 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2064 assert(add.type().equals(intfn2));
2065 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2066 assert(twice.type().equals(intfn1));
2067 assert((int)twice.invokeExact(21) == 42);
2068 * }</pre></blockquote>
2069 * @param target the method handle to invoke after arguments are reordered
2070 * @param newType the expected type of the new method handle
2071 * @param reorder an index array which controls the reordering
2072 * @return a method handle which delegates to the target after it
2073 * drops unused arguments and moves and/or duplicates the other arguments
2074 * @throws NullPointerException if any argument is null
2075 * @throws IllegalArgumentException if the index array length is not equal to
2076 * the arity of the target, or if any index array element
2077 * not a valid index for a parameter of {@code newType},
2078 * or if two corresponding parameter types in
2079 * {@code target.type()} and {@code newType} are not identical,
2080 */
2081 public static
2082 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2083 reorder = reorder.clone();
2084 checkReorder(reorder, newType, target.type());
2085 return target.permuteArguments(newType, reorder);
2086 }
2087
2088 private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
2089 if (newType.returnType() != oldType.returnType())
2090 throw newIllegalArgumentException("return types do not match",
2091 oldType, newType);
2092 if (reorder.length == oldType.parameterCount()) {
2093 int limit = newType.parameterCount();
2094 boolean bad = false;
2095 for (int j = 0; j < reorder.length; j++) {
2096 int i = reorder[j];
2097 if (i < 0 || i >= limit) {
2098 bad = true; break;
2099 }
2100 Class<?> src = newType.parameterType(i);
2101 Class<?> dst = oldType.parameterType(j);
2102 if (src != dst)
2103 throw newIllegalArgumentException("parameter types do not match after reorder",
2104 oldType, newType);
2105 }
2106 if (!bad) return;
2107 }
2108 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2109 }
2110
2111 /**
2112 * Produces a method handle of the requested return type which returns the given
2113 * constant value every time it is invoked.
2114 * <p>
2115 * Before the method handle is returned, the passed-in value is converted to the requested type.
2116 * If the requested type is primitive, widening primitive conversions are attempted,
2117 * else reference conversions are attempted.
2118 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2119 * @param type the return type of the desired method handle
2120 * @param value the value to return
2121 * @return a method handle of the given return type and no arguments, which always returns the given value
2122 * @throws NullPointerException if the {@code type} argument is null
2123 * @throws ClassCastException if the value cannot be converted to the required return type
2124 * @throws IllegalArgumentException if the given type is {@code void.class}
2125 */
2126 public static
2127 MethodHandle constant(Class<?> type, Object value) {
2128 if (type.isPrimitive()) {
2129 if (type == void.class)
2130 throw newIllegalArgumentException("void type");
2131 Wrapper w = Wrapper.forPrimitiveType(type);
2132 return insertArguments(identity(type), 0, w.convert(value, type));
2133 } else {
2134 return identity(type).bindTo(type.cast(value));
2135 }
2136 }
2137
2138 /**
2139 * Produces a method handle which returns its sole argument when invoked.
2140 * @param type the type of the sole parameter and return value of the desired method handle
2141 * @return a unary method handle which accepts and returns the given type
2142 * @throws NullPointerException if the argument is null
2143 * @throws IllegalArgumentException if the given type is {@code void.class}
2144 */
2145 public static
2146 MethodHandle identity(Class<?> type) {
2147 if (type == void.class)
2148 throw newIllegalArgumentException("void type");
2149 else if (type == Object.class)
2150 return ValueConversions.identity();
2151 else if (type.isPrimitive())
2152 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
2153 else
2154 return MethodHandleImpl.makeReferenceIdentity(type);
2155 }
2156
2157 /**
2158 * Provides a target method handle with one or more <em>bound arguments</em>
2159 * in advance of the method handle's invocation.
2160 * The formal parameters to the target corresponding to the bound
2161 * arguments are called <em>bound parameters</em>.
2162 * Returns a new method handle which saves away the bound arguments.
2163 * When it is invoked, it receives arguments for any non-bound parameters,
2164 * binds the saved arguments to their corresponding parameters,
2165 * and calls the original target.
2166 * <p>
2167 * The type of the new method handle will drop the types for the bound
2168 * parameters from the original target type, since the new method handle
2169 * will no longer require those arguments to be supplied by its callers.
2170 * <p>
2171 * Each given argument object must match the corresponding bound parameter type.
2172 * If a bound parameter type is a primitive, the argument object
2173 * must be a wrapper, and will be unboxed to produce the primitive value.
2174 * <p>
2175 * The {@code pos} argument selects which parameters are to be bound.
2176 * It may range between zero and <i>N-L</i> (inclusively),
2177 * where <i>N</i> is the arity of the target method handle
2178 * and <i>L</i> is the length of the values array.
2179 * @param target the method handle to invoke after the argument is inserted
2180 * @param pos where to insert the argument (zero for the first)
2181 * @param values the series of arguments to insert
2182 * @return a method handle which inserts an additional argument,
2183 * before calling the original method handle
2184 * @throws NullPointerException if the target or the {@code values} array is null
2185 * @see MethodHandle#bindTo
2186 */
2187 public static
2188 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2189 int insCount = values.length;
2190 MethodType oldType = target.type();
2191 int outargs = oldType.parameterCount();
2192 int inargs = outargs - insCount;
2193 if (inargs < 0)
2194 throw newIllegalArgumentException("too many values to insert");
2195 if (pos < 0 || pos > inargs)
2196 throw newIllegalArgumentException("no argument type to append");
2197 MethodHandle result = target;
2198 for (int i = 0; i < insCount; i++) {
2199 Object value = values[i];
2200 Class<?> ptype = oldType.parameterType(pos+i);
2201 if (ptype.isPrimitive()) {
2202 BasicType btype = I_TYPE;
2203 Wrapper w = Wrapper.forPrimitiveType(ptype);
2204 switch (w) {
2205 case LONG: btype = J_TYPE; break;
2206 case FLOAT: btype = F_TYPE; break;
2207 case DOUBLE: btype = D_TYPE; break;
2208 }
2209 // perform unboxing and/or primitive conversion
2210 value = w.convert(value, ptype);
2211 result = result.bindArgument(pos, btype, value);
2212 continue;
2213 }
2214 value = ptype.cast(value); // throw CCE if needed
2215 if (pos == 0) {
2216 result = result.bindReceiver(value);
2217 } else {
2218 result = result.bindArgument(pos, L_TYPE, value);
2219 }
2220 }
2221 return result;
2222 }
2223
2224 /**
2225 * Produces a method handle which will discard some dummy arguments
2226 * before calling some other specified <i>target</i> method handle.
2227 * The type of the new method handle will be the same as the target's type,
2228 * except it will also include the dummy argument types,
2229 * at some given position.
2230 * <p>
2231 * The {@code pos} argument may range between zero and <i>N</i>,
2232 * where <i>N</i> is the arity of the target.
2233 * If {@code pos} is zero, the dummy arguments will precede
2234 * the target's real arguments; if {@code pos} is <i>N</i>
2235 * they will come after.
2236 * <p>
2237 * <b>Example:</b>
2238 * <blockquote><pre>{@code
2239 import static java.lang.invoke.MethodHandles.*;
2240 import static java.lang.invoke.MethodType.*;
2241 ...
2242 MethodHandle cat = lookup().findVirtual(String.class,
2243 "concat", methodType(String.class, String.class));
2244 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2245 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2246 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2247 assertEquals(bigType, d0.type());
2248 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2249 * }</pre></blockquote>
2250 * <p>
2251 * This method is also equivalent to the following code:
2252 * <blockquote><pre>
2253 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2254 * </pre></blockquote>
2255 * @param target the method handle to invoke after the arguments are dropped
2256 * @param valueTypes the type(s) of the argument(s) to drop
2257 * @param pos position of first argument to drop (zero for the leftmost)
2258 * @return a method handle which drops arguments of the given types,
2259 * before calling the original method handle
2260 * @throws NullPointerException if the target is null,
2261 * or if the {@code valueTypes} list or any of its elements is null
2262 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2263 * or if {@code pos} is negative or greater than the arity of the target,
2264 * or if the new method handle's type would have too many parameters
2265 */
2266 public static
2267 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2268 MethodType oldType = target.type(); // get NPE
2269 int dropped = valueTypes.size();
2270 MethodType.checkSlotCount(dropped);
2271 if (dropped == 0) return target;
2272 int outargs = oldType.parameterCount();
2273 int inargs = outargs + dropped;
2274 if (pos < 0 || pos >= inargs)
2275 throw newIllegalArgumentException("no argument type to remove");
2276 ArrayList<Class<?>> ptypes = new ArrayList<>(oldType.parameterList());
2277 ptypes.addAll(pos, valueTypes);
2278 if (ptypes.size() != inargs) throw newIllegalArgumentException("valueTypes");
2279 MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
2280 return target.dropArguments(newType, pos, dropped);
2281 }
2282
2283 /**
2284 * Produces a method handle which will discard some dummy arguments
2285 * before calling some other specified <i>target</i> method handle.
2286 * The type of the new method handle will be the same as the target's type,
2287 * except it will also include the dummy argument types,
2288 * at some given position.
2289 * <p>
2290 * The {@code pos} argument may range between zero and <i>N</i>,
2291 * where <i>N</i> is the arity of the target.
2292 * If {@code pos} is zero, the dummy arguments will precede
2293 * the target's real arguments; if {@code pos} is <i>N</i>
2294 * they will come after.
2295 * <p>
2296 * <b>Example:</b>
2297 * <blockquote><pre>{@code
2298 import static java.lang.invoke.MethodHandles.*;
2299 import static java.lang.invoke.MethodType.*;
2300 ...
2301 MethodHandle cat = lookup().findVirtual(String.class,
2302 "concat", methodType(String.class, String.class));
2303 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2304 MethodHandle d0 = dropArguments(cat, 0, String.class);
2305 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2306 MethodHandle d1 = dropArguments(cat, 1, String.class);
2307 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2308 MethodHandle d2 = dropArguments(cat, 2, String.class);
2309 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2310 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2311 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2312 * }</pre></blockquote>
2313 * <p>
2314 * This method is also equivalent to the following code:
2315 * <blockquote><pre>
2316 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2317 * </pre></blockquote>
2318 * @param target the method handle to invoke after the arguments are dropped
2319 * @param valueTypes the type(s) of the argument(s) to drop
2320 * @param pos position of first argument to drop (zero for the leftmost)
2321 * @return a method handle which drops arguments of the given types,
2322 * before calling the original method handle
2323 * @throws NullPointerException if the target is null,
2324 * or if the {@code valueTypes} array or any of its elements is null
2325 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2326 * or if {@code pos} is negative or greater than the arity of the target,
2327 * or if the new method handle's type would have
2328 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2329 */
2330 public static
2331 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2332 return dropArguments(target, pos, Arrays.asList(valueTypes));
2333 }
2334
2335 /**
2336 * Adapts a target method handle by pre-processing
2337 * one or more of its arguments, each with its own unary filter function,
2338 * and then calling the target with each pre-processed argument
2339 * replaced by the result of its corresponding filter function.
2340 * <p>
2341 * The pre-processing is performed by one or more method handles,
2342 * specified in the elements of the {@code filters} array.
2343 * The first element of the filter array corresponds to the {@code pos}
2344 * argument of the target, and so on in sequence.
2345 * <p>
2346 * Null arguments in the array are treated as identity functions,
2347 * and the corresponding arguments left unchanged.
2348 * (If there are no non-null elements in the array, the original target is returned.)
2349 * Each filter is applied to the corresponding argument of the adapter.
2350 * <p>
2351 * If a filter {@code F} applies to the {@code N}th argument of
2352 * the target, then {@code F} must be a method handle which
2353 * takes exactly one argument. The type of {@code F}'s sole argument
2354 * replaces the corresponding argument type of the target
2355 * in the resulting adapted method handle.
2356 * The return type of {@code F} must be identical to the corresponding
2357 * parameter type of the target.
2358 * <p>
2359 * It is an error if there are elements of {@code filters}
2360 * (null or not)
2361 * which do not correspond to argument positions in the target.
2362 * <p><b>Example:</b>
2363 * <blockquote><pre>{@code
2364 import static java.lang.invoke.MethodHandles.*;
2365 import static java.lang.invoke.MethodType.*;
2366 ...
2367 MethodHandle cat = lookup().findVirtual(String.class,
2368 "concat", methodType(String.class, String.class));
2369 MethodHandle upcase = lookup().findVirtual(String.class,
2370 "toUpperCase", methodType(String.class));
2371 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2372 MethodHandle f0 = filterArguments(cat, 0, upcase);
2373 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2374 MethodHandle f1 = filterArguments(cat, 1, upcase);
2375 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2376 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2377 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2378 * }</pre></blockquote>
2379 * <p> Here is pseudocode for the resulting adapter:
2380 * <blockquote><pre>{@code
2381 * V target(P... p, A[i]... a[i], B... b);
2382 * A[i] filter[i](V[i]);
2383 * T adapter(P... p, V[i]... v[i], B... b) {
2384 * return target(p..., f[i](v[i])..., b...);
2385 * }
2386 * }</pre></blockquote>
2387 *
2388 * @param target the method handle to invoke after arguments are filtered
2389 * @param pos the position of the first argument to filter
2390 * @param filters method handles to call initially on filtered arguments
2391 * @return method handle which incorporates the specified argument filtering logic
2392 * @throws NullPointerException if the target is null
2393 * or if the {@code filters} array is null
2394 * @throws IllegalArgumentException if a non-null element of {@code filters}
2395 * does not match a corresponding argument type of target as described above,
2396 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2397 * or if the resulting method handle's type would have
2398 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2399 */
2400 public static
2401 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2402 MethodType targetType = target.type();
2403 MethodHandle adapter = target;
2404 MethodType adapterType = null;
2405 assert((adapterType = targetType) != null);
2406 int maxPos = targetType.parameterCount();
2407 if (pos + filters.length > maxPos)
2408 throw newIllegalArgumentException("too many filters");
2409 int curPos = pos-1; // pre-incremented
2410 for (MethodHandle filter : filters) {
2411 curPos += 1;
2412 if (filter == null) continue; // ignore null elements of filters
2413 adapter = filterArgument(adapter, curPos, filter);
2414 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
2415 }
2416 assert(adapterType.equals(adapter.type()));
2417 return adapter;
2418 }
2419
2420 /*non-public*/ static
2421 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2422 MethodType targetType = target.type();
2423 MethodType filterType = filter.type();
2424 if (filterType.parameterCount() != 1
2425 || filterType.returnType() != targetType.parameterType(pos))
2426 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2427 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2428 }
2429
2430 /**
2431 * Adapts a target method handle by pre-processing
2432 * a sub-sequence of its arguments with a filter (another method handle).
2433 * The pre-processed arguments are replaced by the result (if any) of the
2434 * filter function.
2435 * The target is then called on the modified (usually shortened) argument list.
2436 * <p>
2437 * If the filter returns a value, the target must accept that value as
2438 * its argument in position {@code pos}, preceded and/or followed by
2439 * any arguments not passed to the filter.
2440 * If the filter returns void, the target must accept all arguments
2441 * not passed to the filter.
2442 * No arguments are reordered, and a result returned from the filter
2443 * replaces (in order) the whole subsequence of arguments originally
2444 * passed to the adapter.
2445 * <p>
2446 * The argument types (if any) of the filter
2447 * replace zero or one argument types of the target, at position {@code pos},
2448 * in the resulting adapted method handle.
2449 * The return type of the filter (if any) must be identical to the
2450 * argument type of the target at position {@code pos}, and that target argument
2451 * is supplied by the return value of the filter.
2452 * <p>
2453 * In all cases, {@code pos} must be greater than or equal to zero, and
2454 * {@code pos} must also be less than or equal to the target's arity.
2455 * <p><b>Example:</b>
2456 * <blockquote><pre>{@code
2457 import static java.lang.invoke.MethodHandles.*;
2458 import static java.lang.invoke.MethodType.*;
2459 ...
2460 MethodHandle deepToString = publicLookup()
2461 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2462
2463 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2464 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2465
2466 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2467 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2468
2469 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2470 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2471 assertEquals("[top, [up, down], strange]",
2472 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2473
2474 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2475 assertEquals("[top, [up, down], [strange]]",
2476 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2477
2478 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2479 assertEquals("[top, [[up, down, strange], charm], bottom]",
2480 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2481 * }</pre></blockquote>
2482 * <p> Here is pseudocode for the resulting adapter:
2483 * <blockquote><pre>{@code
2484 * T target(A...,V,C...);
2485 * V filter(B...);
2486 * T adapter(A... a,B... b,C... c) {
2487 * V v = filter(b...);
2488 * return target(a...,v,c...);
2489 * }
2490 * // and if the filter has no arguments:
2491 * T target2(A...,V,C...);
2492 * V filter2();
2493 * T adapter2(A... a,C... c) {
2494 * V v = filter2();
2495 * return target2(a...,v,c...);
2496 * }
2497 * // and if the filter has a void return:
2498 * T target3(A...,C...);
2499 * void filter3(B...);
2500 * void adapter3(A... a,B... b,C... c) {
2501 * filter3(b...);
2502 * return target3(a...,c...);
2503 * }
2504 * }</pre></blockquote>
2505 * <p>
2506 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2507 * one which first "folds" the affected arguments, and then drops them, in separate
2508 * steps as follows:
2509 * <blockquote><pre>{@code
2510 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2511 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2512 * }</pre></blockquote>
2513 * If the target method handle consumes no arguments besides than the result
2514 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2515 * is equivalent to {@code filterReturnValue(coll, mh)}.
2516 * If the filter method handle {@code coll} consumes one argument and produces
2517 * a non-void result, then {@code collectArguments(mh, N, coll)}
2518 * is equivalent to {@code filterArguments(mh, N, coll)}.
2519 * Other equivalences are possible but would require argument permutation.
2520 *
2521 * @param target the method handle to invoke after filtering the subsequence of arguments
2522 * @param pos the position of the first adapter argument to pass to the filter,
2523 * and/or the target argument which receives the result of the filter
2524 * @param filter method handle to call on the subsequence of arguments
2525 * @return method handle which incorporates the specified argument subsequence filtering logic
2526 * @throws NullPointerException if either argument is null
2527 * @throws IllegalArgumentException if the return type of {@code filter}
2528 * is non-void and is not the same as the {@code pos} argument of the target,
2529 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2530 * or if the resulting method handle's type would have
2531 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2532 * @see MethodHandles#foldArguments
2533 * @see MethodHandles#filterArguments
2534 * @see MethodHandles#filterReturnValue
2535 */
2536 public static
2537 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2538 MethodType targetType = target.type();
2539 MethodType filterType = filter.type();
2540 if (filterType.returnType() != void.class &&
2541 filterType.returnType() != targetType.parameterType(pos))
2542 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2543 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2544 }
2545
2546 /**
2547 * Adapts a target method handle by post-processing
2548 * its return value (if any) with a filter (another method handle).
2549 * The result of the filter is returned from the adapter.
2550 * <p>
2551 * If the target returns a value, the filter must accept that value as
2552 * its only argument.
2553 * If the target returns void, the filter must accept no arguments.
2554 * <p>
2555 * The return type of the filter
2556 * replaces the return type of the target
2557 * in the resulting adapted method handle.
2558 * The argument type of the filter (if any) must be identical to the
2559 * return type of the target.
2560 * <p><b>Example:</b>
2561 * <blockquote><pre>{@code
2562 import static java.lang.invoke.MethodHandles.*;
2563 import static java.lang.invoke.MethodType.*;
2564 ...
2565 MethodHandle cat = lookup().findVirtual(String.class,
2566 "concat", methodType(String.class, String.class));
2567 MethodHandle length = lookup().findVirtual(String.class,
2568 "length", methodType(int.class));
2569 System.out.println((String) cat.invokeExact("x", "y")); // xy
2570 MethodHandle f0 = filterReturnValue(cat, length);
2571 System.out.println((int) f0.invokeExact("x", "y")); // 2
2572 * }</pre></blockquote>
2573 * <p> Here is pseudocode for the resulting adapter:
2574 * <blockquote><pre>{@code
2575 * V target(A...);
2576 * T filter(V);
2577 * T adapter(A... a) {
2578 * V v = target(a...);
2579 * return filter(v);
2580 * }
2581 * // and if the target has a void return:
2582 * void target2(A...);
2583 * T filter2();
2584 * T adapter2(A... a) {
2585 * target2(a...);
2586 * return filter2();
2587 * }
2588 * // and if the filter has a void return:
2589 * V target3(A...);
2590 * void filter3(V);
2591 * void adapter3(A... a) {
2592 * V v = target3(a...);
2593 * filter3(v);
2594 * }
2595 * }</pre></blockquote>
2596 * @param target the method handle to invoke before filtering the return value
2597 * @param filter method handle to call on the return value
2598 * @return method handle which incorporates the specified return value filtering logic
2599 * @throws NullPointerException if either argument is null
2600 * @throws IllegalArgumentException if the argument list of {@code filter}
2601 * does not match the return type of target as described above
2602 */
2603 public static
2604 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2605 MethodType targetType = target.type();
2606 MethodType filterType = filter.type();
2607 Class<?> rtype = targetType.returnType();
2608 int filterValues = filterType.parameterCount();
2609 if (filterValues == 0
2610 ? (rtype != void.class)
2611 : (rtype != filterType.parameterType(0)))
2612 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2613 // result = fold( lambda(retval, arg...) { filter(retval) },
2614 // lambda( arg...) { target(arg...) } )
2615 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2616 }
2617
2618 /**
2619 * Adapts a target method handle by pre-processing
2620 * some of its arguments, and then calling the target with
2621 * the result of the pre-processing, inserted into the original
2622 * sequence of arguments.
2623 * <p>
2624 * The pre-processing is performed by {@code combiner}, a second method handle.
2625 * Of the arguments passed to the adapter, the first {@code N} arguments
2626 * are copied to the combiner, which is then called.
2627 * (Here, {@code N} is defined as the parameter count of the combiner.)
2628 * After this, control passes to the target, with any result
2629 * from the combiner inserted before the original {@code N} incoming
2630 * arguments.
2631 * <p>
2632 * If the combiner returns a value, the first parameter type of the target
2633 * must be identical with the return type of the combiner, and the next
2634 * {@code N} parameter types of the target must exactly match the parameters
2635 * of the combiner.
2636 * <p>
2637 * If the combiner has a void return, no result will be inserted,
2638 * and the first {@code N} parameter types of the target
2639 * must exactly match the parameters of the combiner.
2640 * <p>
2641 * The resulting adapter is the same type as the target, except that the
2642 * first parameter type is dropped,
2643 * if it corresponds to the result of the combiner.
2644 * <p>
2645 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2646 * that either the combiner or the target does not wish to receive.
2647 * If some of the incoming arguments are destined only for the combiner,
2648 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2649 * arguments will not need to be live on the stack on entry to the
2650 * target.)
2651 * <p><b>Example:</b>
2652 * <blockquote><pre>{@code
2653 import static java.lang.invoke.MethodHandles.*;
2654 import static java.lang.invoke.MethodType.*;
2655 ...
2656 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2657 "println", methodType(void.class, String.class))
2658 .bindTo(System.out);
2659 MethodHandle cat = lookup().findVirtual(String.class,
2660 "concat", methodType(String.class, String.class));
2661 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2662 MethodHandle catTrace = foldArguments(cat, trace);
2663 // also prints "boo":
2664 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2665 * }</pre></blockquote>
2666 * <p> Here is pseudocode for the resulting adapter:
2667 * <blockquote><pre>{@code
2668 * // there are N arguments in A...
2669 * T target(V, A[N]..., B...);
2670 * V combiner(A...);
2671 * T adapter(A... a, B... b) {
2672 * V v = combiner(a...);
2673 * return target(v, a..., b...);
2674 * }
2675 * // and if the combiner has a void return:
2676 * T target2(A[N]..., B...);
2677 * void combiner2(A...);
2678 * T adapter2(A... a, B... b) {
2679 * combiner2(a...);
2680 * return target2(a..., b...);
2681 * }
2682 * }</pre></blockquote>
2683 * @param target the method handle to invoke after arguments are combined
2684 * @param combiner method handle to call initially on the incoming arguments
2685 * @return method handle which incorporates the specified argument folding logic
2686 * @throws NullPointerException if either argument is null
2687 * @throws IllegalArgumentException if {@code combiner}'s return type
2688 * is non-void and not the same as the first argument type of
2689 * the target, or if the initial {@code N} argument types
2690 * of the target
2691 * (skipping one matching the {@code combiner}'s return type)
2692 * are not identical with the argument types of {@code combiner}
2693 */
2694 public static
2695 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2696 int pos = 0;
2697 MethodType targetType = target.type();
2698 MethodType combinerType = combiner.type();
2699 int foldPos = pos;
2700 int foldArgs = combinerType.parameterCount();
2701 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2702 int afterInsertPos = foldPos + foldVals;
2703 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2704 if (ok && !(combinerType.parameterList()
2705 .equals(targetType.parameterList().subList(afterInsertPos,
2706 afterInsertPos + foldArgs))))
2707 ok = false;
2708 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2709 ok = false;
2710 if (!ok)
2711 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2712 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2713 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2714 }
2715
2716 /**
2717 * Makes a method handle which adapts a target method handle,
2718 * by guarding it with a test, a boolean-valued method handle.
2719 * If the guard fails, a fallback handle is called instead.
2720 * All three method handles must have the same corresponding
2721 * argument and return types, except that the return type
2722 * of the test must be boolean, and the test is allowed
2723 * to have fewer arguments than the other two method handles.
2724 * <p> Here is pseudocode for the resulting adapter:
2725 * <blockquote><pre>{@code
2726 * boolean test(A...);
2727 * T target(A...,B...);
2728 * T fallback(A...,B...);
2729 * T adapter(A... a,B... b) {
2730 * if (test(a...))
2731 * return target(a..., b...);
2732 * else
2733 * return fallback(a..., b...);
2734 * }
2735 * }</pre></blockquote>
2736 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2737 * be modified by execution of the test, and so are passed unchanged
2738 * from the caller to the target or fallback as appropriate.
2739 * @param test method handle used for test, must return boolean
2740 * @param target method handle to call if test passes
2741 * @param fallback method handle to call if test fails
2742 * @return method handle which incorporates the specified if/then/else logic
2743 * @throws NullPointerException if any argument is null
2744 * @throws IllegalArgumentException if {@code test} does not return boolean,
2745 * or if all three method types do not match (with the return
2746 * type of {@code test} changed to match that of the target).
2747 */
2748 public static
2749 MethodHandle guardWithTest(MethodHandle test,
2750 MethodHandle target,
2751 MethodHandle fallback) {
2752 MethodType gtype = test.type();
2753 MethodType ttype = target.type();
2754 MethodType ftype = fallback.type();
2755 if (!ttype.equals(ftype))
2756 throw misMatchedTypes("target and fallback types", ttype, ftype);
2757 if (gtype.returnType() != boolean.class)
2758 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2759 List<Class<?>> targs = ttype.parameterList();
2760 List<Class<?>> gargs = gtype.parameterList();
2761 if (!targs.equals(gargs)) {
2762 int gpc = gargs.size(), tpc = targs.size();
2763 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2764 throw misMatchedTypes("target and test types", ttype, gtype);
2765 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2766 gtype = test.type();
2767 }
2768 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2769 }
2770
2771 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2772 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2773 }
2774
2775 /**
2776 * Makes a method handle which adapts a target method handle,
2777 * by running it inside an exception handler.
2778 * If the target returns normally, the adapter returns that value.
2779 * If an exception matching the specified type is thrown, the fallback
2780 * handle is called instead on the exception, plus the original arguments.
2781 * <p>
2782 * The target and handler must have the same corresponding
2783 * argument and return types, except that handler may omit trailing arguments
2784 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2785 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2786 * <p> Here is pseudocode for the resulting adapter:
2787 * <blockquote><pre>{@code
2788 * T target(A..., B...);
2789 * T handler(ExType, A...);
2790 * T adapter(A... a, B... b) {
2791 * try {
2792 * return target(a..., b...);
2793 * } catch (ExType ex) {
2794 * return handler(ex, a...);
2795 * }
2796 * }
2797 * }</pre></blockquote>
2798 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2799 * be modified by execution of the target, and so are passed unchanged
2800 * from the caller to the handler, if the handler is invoked.
2801 * <p>
2802 * The target and handler must return the same type, even if the handler
2803 * always throws. (This might happen, for instance, because the handler
2804 * is simulating a {@code finally} clause).
2805 * To create such a throwing handler, compose the handler creation logic
2806 * with {@link #throwException throwException},
2807 * in order to create a method handle of the correct return type.
2808 * @param target method handle to call
2809 * @param exType the type of exception which the handler will catch
2810 * @param handler method handle to call if a matching exception is thrown
2811 * @return method handle which incorporates the specified try/catch logic
2812 * @throws NullPointerException if any argument is null
2813 * @throws IllegalArgumentException if {@code handler} does not accept
2814 * the given exception type, or if the method handle types do
2815 * not match in their return types and their
2816 * corresponding parameters
2817 */
2818 public static
2819 MethodHandle catchException(MethodHandle target,
2820 Class<? extends Throwable> exType,
2821 MethodHandle handler) {
2822 MethodType ttype = target.type();
2823 MethodType htype = handler.type();
2824 if (htype.parameterCount() < 1 ||
2825 !htype.parameterType(0).isAssignableFrom(exType))
2826 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2827 if (htype.returnType() != ttype.returnType())
2828 throw misMatchedTypes("target and handler return types", ttype, htype);
2829 List<Class<?>> targs = ttype.parameterList();
2830 List<Class<?>> hargs = htype.parameterList();
2831 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2832 if (!targs.equals(hargs)) {
2833 int hpc = hargs.size(), tpc = targs.size();
2834 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2835 throw misMatchedTypes("target and handler types", ttype, htype);
2836 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2837 htype = handler.type();
2838 }
2839 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2840 }
2841
2842 /**
2843 * Produces a method handle which will throw exceptions of the given {@code exType}.
2844 * The method handle will accept a single argument of {@code exType},
2845 * and immediately throw it as an exception.
2846 * The method type will nominally specify a return of {@code returnType}.
2847 * The return type may be anything convenient: It doesn't matter to the
2848 * method handle's behavior, since it will never return normally.
2849 * @param returnType the return type of the desired method handle
2850 * @param exType the parameter type of the desired method handle
2851 * @return method handle which can throw the given exceptions
2852 * @throws NullPointerException if either argument is null
2853 */
2854 public static
2855 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2856 if (!Throwable.class.isAssignableFrom(exType))
2857 throw new ClassCastException(exType.getName());
2858 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2859 }
2860 }