1 /* 2 * Copyright (c) 2012, 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.io.Serializable; 29 import java.util.Arrays; 30 31 /** 32 * <p>Methods to facilitate the creation of simple "function objects" that 33 * implement one or more interfaces by delegation to a provided {@link MethodHandle}, 34 * possibly after type adaptation and partial evaluation of arguments. These 35 * methods are typically used as <em>bootstrap methods</em> for {@code invokedynamic} 36 * call sites, to support the <em>lambda expression</em> and <em>method 37 * reference expression</em> features of the Java Programming Language. 38 * 39 * <p>Indirect access to the behavior specified by the provided {@code MethodHandle} 40 * proceeds in order through three phases: 41 * <ul> 42 * <li><em>Linkage</em> occurs when the methods in this class are invoked. 43 * They take as arguments an interface to be implemented (typically a 44 * <em>functional interface</em>, one with a single abstract method), a 45 * name and signature of a method from that interface to be implemented, a 46 * method handle describing the desired implementation behavior 47 * for that method, and possibly other additional metadata, and produce a 48 * {@link CallSite} whose target can be used to create suitable function 49 * objects. Linkage may involve dynamically loading a new class that 50 * implements the target interface. The {@code CallSite} can be considered a 51 * "factory" for function objects and so these linkage methods are referred 52 * to as "metafactories".</li> 53 * 54 * <li><em>Capture</em> occurs when the {@code CallSite}'s target is 55 * invoked, typically through an {@code invokedynamic} call site, 56 * producing a function object. This may occur many times for 57 * a single factory {@code CallSite}. Capture may involve allocation of a 58 * new function object, or may return an existing function object. The 59 * behavior {@code MethodHandle} may have additional parameters beyond those 60 * of the specified interface method; these are referred to as <em>captured 61 * parameters</em>, which must be provided as arguments to the 62 * {@code CallSite} target, and which may be early-bound to the behavior 63 * {@code MethodHandle}. The number of captured parameters and their types 64 * are determined during linkage.</li> 65 * 66 * <li><em>Invocation</em> occurs when an implemented interface method 67 * is invoked on a function object. This may occur many times for a single 68 * function object. The method referenced by the behavior {@code MethodHandle} 69 * is invoked with the captured arguments and any additional arguments 70 * provided on invocation, as if by {@link MethodHandle#invoke(Object...)}.</li> 71 * </ul> 72 * 73 * <p>It is sometimes useful to restrict the set of inputs or results permitted 74 * at invocation. For example, when the generic interface {@code Predicate<T>} 75 * is parameterized as {@code Predicate<String>}, the input must be a 76 * {@code String}, even though the method to implement allows any {@code Object}. 77 * At linkage time, an additional {@link MethodType} parameter describes the 78 * "instantiated" method type; on invocation, the arguments and eventual result 79 * are checked against this {@code MethodType}. 80 * 81 * <p>This class provides two forms of linkage methods: a standard version 82 * ({@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)}) 83 * using an optimized protocol, and an alternate version 84 * {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}). 85 * The alternate version is a generalization of the standard version, providing 86 * additional control over the behavior of the generated function objects via 87 * flags and additional arguments. The alternate version adds the ability to 88 * manage the following attributes of function objects: 89 * 90 * <ul> 91 * <li><em>Bridging.</em> It is sometimes useful to implement multiple 92 * variations of the method signature, involving argument or return type 93 * adaptation. This occurs when multiple distinct VM signatures for a method 94 * are logically considered to be the same method by the language. The 95 * flag {@code FLAG_BRIDGES} indicates that a list of additional 96 * {@code MethodType}s will be provided, each of which will be implemented 97 * by the resulting function object. These methods will share the same 98 * name and instantiated type.</li> 99 * 100 * <li><em>Multiple interfaces.</em> If needed, more than one interface 101 * can be implemented by the function object. (These additional interfaces 102 * are typically marker interfaces with no methods.) The flag {@code FLAG_MARKERS} 103 * indicates that a list of additional interfaces will be provided, each of 104 * which should be implemented by the resulting function object.</li> 105 * 106 * <li><em>Serializability.</em> The generated function objects do not 107 * generally support serialization. If desired, {@code FLAG_SERIALIZABLE} 108 * can be used to indicate that the function objects should be serializable. 109 * Serializable function objects will use, as their serialized form, 110 * instances of the class {@code SerializedLambda}, which requires additional 111 * assistance from the capturing class (the class described by the 112 * {@link MethodHandles.Lookup} parameter {@code caller}); see 113 * {@link SerializedLambda} for details.</li> 114 * </ul> 115 * 116 * <p>Assume the linkage arguments are as follows: 117 * <ul> 118 * <li>{@code invokedType} (describing the {@code CallSite} signature) has 119 * K parameters of types (D1..Dk) and return type Rd;</li> 120 * <li>{@code samMethodType} (describing the implemented method type) has N 121 * parameters, of types (U1..Un) and return type Ru;</li> 122 * <li>{@code implMethod} (the {@code MethodHandle} providing the 123 * implementation has M parameters, of types (A1..Am) and return type Ra 124 * (if the method describes an instance method, the method type of this 125 * method handle already includes an extra first argument corresponding to 126 * the receiver);</li> 127 * <li>{@code instantiatedMethodType} (allowing restrictions on invocation) 128 * has N parameters, of types (T1..Tn) and return type Rt.</li> 129 * </ul> 130 * 131 * <p>Then the following linkage invariants must hold: 132 * <ul> 133 * <li>Rd is an interface</li> 134 * <li>{@code implMethod} is a <em>direct method handle</em></li> 135 * <li>{@code samMethodType} and {@code instantiatedMethodType} have the same 136 * arity N, and for i=1..N, Ti and Ui are the same type, or Ti and Ui are 137 * both reference types and Ti is a subtype of Ui</li> 138 * <li>Either Rt and Ru are the same type, or both are reference types and 139 * Rt is a subtype of Ru</li> 140 * <li>K + N = M</li> 141 * <li>For i=1..K, Di = Ai</li> 142 * <li>For i=1..N, Ti is adaptable to Aj, where j=i+k</li> 143 * <li>The return type Rt is void, or the return type Ra is not void and is 144 * adaptable to Rt</li> 145 * </ul> 146 * 147 * <p>Further, at capture time, if {@code implMethod} corresponds to an instance 148 * method, and there are any capture arguments ({@code K > 0}), then the first 149 * capture argument (corresponding to the receiver) must be non-null. 150 * 151 * <p>A type Q is considered adaptable to S as follows: 152 * <table> 153 * <caption style="display:none">adaptable types</caption> 154 * <thead> 155 * <tr><th>Q</th><th>S</th><th>Link-time checks</th><th>Invocation-time checks</th></tr> 156 * </thead> 157 * <tbody> 158 * <tr> 159 * <td>Primitive</td><td>Primitive</td> 160 * <td>Q can be converted to S via a primitive widening conversion</td> 161 * <td>None</td> 162 * </tr> 163 * <tr> 164 * <td>Primitive</td><td>Reference</td> 165 * <td>S is a supertype of the Wrapper(Q)</td> 166 * <td>Cast from Wrapper(Q) to S</td> 167 * </tr> 168 * <tr> 169 * <td>Reference</td><td>Primitive</td> 170 * <td>for parameter types: Q is a primitive wrapper and Primitive(Q) 171 * can be widened to S 172 * <br>for return types: If Q is a primitive wrapper, check that 173 * Primitive(Q) can be widened to S</td> 174 * <td>If Q is not a primitive wrapper, cast Q to the base Wrapper(S); 175 * for example Number for numeric types</td> 176 * </tr> 177 * <tr> 178 * <td>Reference</td><td>Reference</td> 179 * <td>for parameter types: S is a supertype of Q 180 * <br>for return types: none</td> 181 * <td>Cast from Q to S</td> 182 * </tr> 183 * </tbody> 184 * </table> 185 * 186 * @apiNote These linkage methods are designed to support the evaluation 187 * of <em>lambda expressions</em> and <em>method references</em> in the Java 188 * Language. For every lambda expressions or method reference in the source code, 189 * there is a target type which is a functional interface. Evaluating a lambda 190 * expression produces an object of its target type. The recommended mechanism 191 * for evaluating lambda expressions is to desugar the lambda body to a method, 192 * invoke an invokedynamic call site whose static argument list describes the 193 * sole method of the functional interface and the desugared implementation 194 * method, and returns an object (the lambda object) that implements the target 195 * type. (For method references, the implementation method is simply the 196 * referenced method; no desugaring is needed.) 197 * 198 * <p>The argument list of the implementation method and the argument list of 199 * the interface method(s) may differ in several ways. The implementation 200 * methods may have additional arguments to accommodate arguments captured by 201 * the lambda expression; there may also be differences resulting from permitted 202 * adaptations of arguments, such as casting, boxing, unboxing, and primitive 203 * widening. (Varargs adaptations are not handled by the metafactories; these are 204 * expected to be handled by the caller.) 205 * 206 * <p>Invokedynamic call sites have two argument lists: a static argument list 207 * and a dynamic argument list. The static argument list is stored in the 208 * constant pool; the dynamic argument is pushed on the operand stack at capture 209 * time. The bootstrap method has access to the entire static argument list 210 * (which in this case, includes information describing the implementation method, 211 * the target interface, and the target interface method(s)), as well as a 212 * method signature describing the number and static types (but not the values) 213 * of the dynamic arguments and the static return type of the invokedynamic site. 214 * 215 * @implNote The implementation method is described with a method handle. In 216 * theory, any method handle could be used. Currently supported are direct method 217 * handles representing invocation of virtual, interface, constructor and static 218 * methods. 219 * @since 1.8 220 */ 221 public class LambdaMetafactory { 222 223 /** Flag for alternate metafactories indicating the lambda object 224 * must be serializable */ 225 public static final int FLAG_SERIALIZABLE = 1 << 0; 226 227 /** 228 * Flag for alternate metafactories indicating the lambda object implements 229 * other marker interfaces 230 * besides Serializable 231 */ 232 public static final int FLAG_MARKERS = 1 << 1; 233 234 /** 235 * Flag for alternate metafactories indicating the lambda object requires 236 * additional bridge methods 237 */ 238 public static final int FLAG_BRIDGES = 1 << 2; 239 240 private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0]; 241 private static final MethodType[] EMPTY_MT_ARRAY = new MethodType[0]; 242 243 /** 244 * Facilitates the creation of simple "function objects" that implement one 245 * or more interfaces by delegation to a provided {@link MethodHandle}, 246 * after appropriate type adaptation and partial evaluation of arguments. 247 * Typically used as a <em>bootstrap method</em> for {@code invokedynamic} 248 * call sites, to support the <em>lambda expression</em> and <em>method 249 * reference expression</em> features of the Java Programming Language. 250 * 251 * <p>This is the standard, streamlined metafactory; additional flexibility 252 * is provided by {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}. 253 * A general description of the behavior of this method is provided 254 * {@link LambdaMetafactory above}. 255 * 256 * <p>When the target of the {@code CallSite} returned from this method is 257 * invoked, the resulting function objects are instances of a class which 258 * implements the interface named by the return type of {@code invokedType}, 259 * declares a method with the name given by {@code invokedName} and the 260 * signature given by {@code samMethodType}. It may also override additional 261 * methods from {@code Object}. 262 * 263 * @param caller Represents a lookup context with the accessibility 264 * privileges of the caller. When used with {@code invokedynamic}, 265 * this is stacked automatically by the VM. 266 * @param invokedName The name of the method to implement. When used with 267 * {@code invokedynamic}, this is provided by the 268 * {@code NameAndType} of the {@code InvokeDynamic} 269 * structure and is stacked automatically by the VM. 270 * @param invokedType The expected signature of the {@code CallSite}. The 271 * parameter types represent the types of capture variables; 272 * the return type is the interface to implement. When 273 * used with {@code invokedynamic}, this is provided by 274 * the {@code NameAndType} of the {@code InvokeDynamic} 275 * structure and is stacked automatically by the VM. 276 * In the event that the implementation method is an 277 * instance method and this signature has any parameters, 278 * the first parameter in the invocation signature must 279 * correspond to the receiver. 280 * @param samMethodType Signature and return type of method to be implemented 281 * by the function object. 282 * @param implMethod A direct method handle describing the implementation 283 * method which should be called (with suitable adaptation 284 * of argument types, return types, and with captured 285 * arguments prepended to the invocation arguments) at 286 * invocation time. 287 * @param instantiatedMethodType The signature and return type that should 288 * be enforced dynamically at invocation time. 289 * This may be the same as {@code samMethodType}, 290 * or may be a specialization of it. 291 * @return a CallSite whose target can be used to perform capture, generating 292 * instances of the interface named by {@code invokedType} 293 * @throws LambdaConversionException If any of the linkage invariants 294 * described {@link LambdaMetafactory above} 295 * are violated 296 */ 297 public static CallSite metafactory(MethodHandles.Lookup caller, 298 String invokedName, 299 MethodType invokedType, 300 MethodType samMethodType, 301 MethodHandle implMethod, 302 MethodType instantiatedMethodType) 303 throws LambdaConversionException { 304 AbstractValidatingLambdaMetafactory mf; 305 mf = new InnerClassLambdaMetafactory(caller, invokedType, 306 invokedName, samMethodType, 307 implMethod, instantiatedMethodType, 308 false, EMPTY_CLASS_ARRAY, EMPTY_MT_ARRAY); 309 mf.validateMetafactoryArgs(); 310 return mf.buildCallSite(); 311 } 312 313 /** 314 * Facilitates the creation of simple "function objects" that implement one 315 * or more interfaces by delegation to a provided {@link MethodHandle}, 316 * after appropriate type adaptation and partial evaluation of arguments. 317 * Typically used as a <em>bootstrap method</em> for {@code invokedynamic} 318 * call sites, to support the <em>lambda expression</em> and <em>method 319 * reference expression</em> features of the Java Programming Language. 320 * 321 * <p>This is the general, more flexible metafactory; a streamlined version 322 * is provided by {@link #metafactory(java.lang.invoke.MethodHandles.Lookup, 323 * String, MethodType, MethodType, MethodHandle, MethodType)}. 324 * A general description of the behavior of this method is provided 325 * {@link LambdaMetafactory above}. 326 * 327 * <p>The argument list for this method includes three fixed parameters, 328 * corresponding to the parameters automatically stacked by the VM for the 329 * bootstrap method in an {@code invokedynamic} invocation, and an {@code Object[]} 330 * parameter that contains additional parameters. The declared argument 331 * list for this method is: 332 * 333 * <pre>{@code 334 * CallSite altMetafactory(MethodHandles.Lookup caller, 335 * String invokedName, 336 * MethodType invokedType, 337 * Object... args) 338 * }</pre> 339 * 340 * <p>but it behaves as if the argument list is as follows: 341 * 342 * <pre>{@code 343 * CallSite altMetafactory(MethodHandles.Lookup caller, 344 * String invokedName, 345 * MethodType invokedType, 346 * MethodType samMethodType, 347 * MethodHandle implMethod, 348 * MethodType instantiatedMethodType, 349 * int flags, 350 * int markerInterfaceCount, // IF flags has MARKERS set 351 * Class... markerInterfaces, // IF flags has MARKERS set 352 * int bridgeCount, // IF flags has BRIDGES set 353 * MethodType... bridges // IF flags has BRIDGES set 354 * ) 355 * }</pre> 356 * 357 * <p>Arguments that appear in the argument list for 358 * {@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)} 359 * have the same specification as in that method. The additional arguments 360 * are interpreted as follows: 361 * <ul> 362 * <li>{@code flags} indicates additional options; this is a bitwise 363 * OR of desired flags. Defined flags are {@link #FLAG_BRIDGES}, 364 * {@link #FLAG_MARKERS}, and {@link #FLAG_SERIALIZABLE}.</li> 365 * <li>{@code markerInterfaceCount} is the number of additional interfaces 366 * the function object should implement, and is present if and only if the 367 * {@code FLAG_MARKERS} flag is set.</li> 368 * <li>{@code markerInterfaces} is a variable-length list of additional 369 * interfaces to implement, whose length equals {@code markerInterfaceCount}, 370 * and is present if and only if the {@code FLAG_MARKERS} flag is set.</li> 371 * <li>{@code bridgeCount} is the number of additional method signatures 372 * the function object should implement, and is present if and only if 373 * the {@code FLAG_BRIDGES} flag is set.</li> 374 * <li>{@code bridges} is a variable-length list of additional 375 * methods signatures to implement, whose length equals {@code bridgeCount}, 376 * and is present if and only if the {@code FLAG_BRIDGES} flag is set.</li> 377 * </ul> 378 * 379 * <p>Each class named by {@code markerInterfaces} is subject to the same 380 * restrictions as {@code Rd}, the return type of {@code invokedType}, 381 * as described {@link LambdaMetafactory above}. Each {@code MethodType} 382 * named by {@code bridges} is subject to the same restrictions as 383 * {@code samMethodType}, as described {@link LambdaMetafactory above}. 384 * 385 * <p>When FLAG_SERIALIZABLE is set in {@code flags}, the function objects 386 * will implement {@code Serializable}, and will have a {@code writeReplace} 387 * method that returns an appropriate {@link SerializedLambda}. The 388 * {@code caller} class must have an appropriate {@code $deserializeLambda$} 389 * method, as described in {@link SerializedLambda}. 390 * 391 * <p>When the target of the {@code CallSite} returned from this method is 392 * invoked, the resulting function objects are instances of a class with 393 * the following properties: 394 * <ul> 395 * <li>The class implements the interface named by the return type 396 * of {@code invokedType} and any interfaces named by {@code markerInterfaces}</li> 397 * <li>The class declares methods with the name given by {@code invokedName}, 398 * and the signature given by {@code samMethodType} and additional signatures 399 * given by {@code bridges}</li> 400 * <li>The class may override methods from {@code Object}, and may 401 * implement methods related to serialization.</li> 402 * </ul> 403 * 404 * @param caller Represents a lookup context with the accessibility 405 * privileges of the caller. When used with {@code invokedynamic}, 406 * this is stacked automatically by the VM. 407 * @param invokedName The name of the method to implement. When used with 408 * {@code invokedynamic}, this is provided by the 409 * {@code NameAndType} of the {@code InvokeDynamic} 410 * structure and is stacked automatically by the VM. 411 * @param invokedType The expected signature of the {@code CallSite}. The 412 * parameter types represent the types of capture variables; 413 * the return type is the interface to implement. When 414 * used with {@code invokedynamic}, this is provided by 415 * the {@code NameAndType} of the {@code InvokeDynamic} 416 * structure and is stacked automatically by the VM. 417 * In the event that the implementation method is an 418 * instance method and this signature has any parameters, 419 * the first parameter in the invocation signature must 420 * correspond to the receiver. 421 * @param args An {@code Object[]} array containing the required 422 * arguments {@code samMethodType}, {@code implMethod}, 423 * {@code instantiatedMethodType}, {@code flags}, and any 424 * optional arguments, as described 425 * {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)} above} 426 * @return a CallSite whose target can be used to perform capture, generating 427 * instances of the interface named by {@code invokedType} 428 * @throws LambdaConversionException If any of the linkage invariants 429 * described {@link LambdaMetafactory above} 430 * are violated 431 */ 432 public static CallSite altMetafactory(MethodHandles.Lookup caller, 433 String invokedName, 434 MethodType invokedType, 435 Object... args) 436 throws LambdaConversionException { 437 MethodType samMethodType = (MethodType)args[0]; 438 MethodHandle implMethod = (MethodHandle)args[1]; 439 MethodType instantiatedMethodType = (MethodType)args[2]; 440 int flags = (Integer) args[3]; 441 Class<?>[] markerInterfaces; 442 MethodType[] bridges; 443 int argIndex = 4; 444 if ((flags & FLAG_MARKERS) != 0) { 445 int markerCount = (Integer) args[argIndex++]; 446 markerInterfaces = new Class<?>[markerCount]; 447 System.arraycopy(args, argIndex, markerInterfaces, 0, markerCount); 448 argIndex += markerCount; 449 } 450 else 451 markerInterfaces = EMPTY_CLASS_ARRAY; 452 if ((flags & FLAG_BRIDGES) != 0) { 453 int bridgeCount = (Integer) args[argIndex++]; 454 bridges = new MethodType[bridgeCount]; 455 System.arraycopy(args, argIndex, bridges, 0, bridgeCount); 456 argIndex += bridgeCount; 457 } 458 else 459 bridges = EMPTY_MT_ARRAY; 460 461 boolean isSerializable = ((flags & FLAG_SERIALIZABLE) != 0); 462 if (isSerializable) { 463 boolean foundSerializableSupertype = Serializable.class.isAssignableFrom(invokedType.returnType()); 464 for (Class<?> c : markerInterfaces) 465 foundSerializableSupertype |= Serializable.class.isAssignableFrom(c); 466 if (!foundSerializableSupertype) { 467 markerInterfaces = Arrays.copyOf(markerInterfaces, markerInterfaces.length + 1); 468 markerInterfaces[markerInterfaces.length-1] = Serializable.class; 469 } 470 } 471 472 AbstractValidatingLambdaMetafactory mf 473 = new InnerClassLambdaMetafactory(caller, invokedType, 474 invokedName, samMethodType, 475 implMethod, 476 instantiatedMethodType, 477 isSerializable, 478 markerInterfaces, bridges); 479 mf.validateMetafactoryArgs(); 480 return mf.buildCallSite(); 481 } 482 }