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