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 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 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 * <p> 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 }