1 /*
2 * Copyright (c) 2008, 2012, 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.security.AccessController;
30 import java.security.PrivilegedAction;
31 import sun.invoke.WrapperInstance;
32 import java.util.ArrayList;
33 import sun.reflect.CallerSensitive;
34 import sun.reflect.Reflection;
35 import sun.reflect.misc.ReflectUtil;
36
37 /**
38 * This class consists exclusively of static methods that help adapt
39 * method handles to other JVM types, such as interfaces.
40 */
41 public class MethodHandleProxies {
42
43 private MethodHandleProxies() { } // do not instantiate
44
45 /**
46 * Produces an instance of the given single-method interface which redirects
47 * its calls to the given method handle.
48 * <p>
49 * A single-method interface is an interface which declares a uniquely named method.
50 * When determining the uniquely named method of a single-method interface,
51 * the public {@code Object} methods ({@code toString}, {@code equals}, {@code hashCode})
52 * are disregarded. For example, {@link java.util.Comparator} is a single-method interface,
53 * even though it re-declares the {@code Object.equals} method.
54 * <p>
55 * The interface must be public. No additional access checks are performed.
56 * <p>
57 * The resulting instance of the required type will respond to
58 * invocation of the type's uniquely named method by calling
59 * the given target on the incoming arguments,
60 * and returning or throwing whatever the target
61 * returns or throws. The invocation will be as if by
62 * {@code target.invoke}.
63 * The target's type will be checked before the
64 * instance is created, as if by a call to {@code asType},
65 * which may result in a {@code WrongMethodTypeException}.
66 * <p>
67 * The uniquely named method is allowed to be multiply declared,
68 * with distinct type descriptors. (E.g., it can be overloaded,
69 * or can possess bridge methods.) All such declarations are
70 * connected directly to the target method handle.
71 * Argument and return types are adjusted by {@code asType}
72 * for each individual declaration.
73 * <p>
74 * The wrapper instance will implement the requested interface
75 * and its super-types, but no other single-method interfaces.
76 * This means that the instance will not unexpectedly
77 * pass an {@code instanceof} test for any unrequested type.
78 * <p style="font-size:smaller;">
79 * <em>Implementation Note:</em>
80 * Therefore, each instance must implement a unique single-method interface.
81 * Implementations may not bundle together
82 * multiple single-method interfaces onto single implementation classes
83 * in the style of {@link java.awt.AWTEventMulticaster}.
84 * <p>
85 * The method handle may throw an <em>undeclared exception</em>,
86 * which means any checked exception (or other checked throwable)
87 * not declared by the requested type's single abstract method.
88 * If this happens, the throwable will be wrapped in an instance of
89 * {@link java.lang.reflect.UndeclaredThrowableException UndeclaredThrowableException}
90 * and thrown in that wrapped form.
91 * <p>
92 * Like {@link java.lang.Integer#valueOf Integer.valueOf},
93 * {@code asInterfaceInstance} is a factory method whose results are defined
94 * by their behavior.
95 * It is not guaranteed to return a new instance for every call.
96 * <p>
97 * Because of the possibility of {@linkplain java.lang.reflect.Method#isBridge bridge methods}
98 * and other corner cases, the interface may also have several abstract methods
99 * with the same name but having distinct descriptors (types of returns and parameters).
100 * In this case, all the methods are bound in common to the one given target.
101 * The type check and effective {@code asType} conversion is applied to each
102 * method type descriptor, and all abstract methods are bound to the target in common.
103 * Beyond this type check, no further checks are made to determine that the
104 * abstract methods are related in any way.
105 * <p>
106 * Future versions of this API may accept additional types,
107 * such as abstract classes with single abstract methods.
108 * Future versions of this API may also equip wrapper instances
109 * with one or more additional public "marker" interfaces.
110 *
111 * @param target the method handle to invoke from the wrapper
112 * @param intfc the desired type of the wrapper, a single-method interface
113 * @return a correctly-typed wrapper for the given target
114 * @throws NullPointerException if either argument is null
115 * @throws IllegalArgumentException if the {@code intfc} is not a
116 * valid argument to this method
117 * @throws WrongMethodTypeException if the target cannot
118 * be converted to the type required by the requested interface
119 */
120 // Other notes to implementors:
121 // <p>
122 // No stable mapping is promised between the single-method interface and
123 // the implementation class C. Over time, several implementation
124 // classes might be used for the same type.
125 // <p>
126 // If the implementation is able
127 // to prove that a wrapper of the required type
128 // has already been created for a given
129 // method handle, or for another method handle with the
130 // same behavior, the implementation may return that wrapper in place of
131 // a new wrapper.
132 // <p>
133 // This method is designed to apply to common use cases
134 // where a single method handle must interoperate with
135 // an interface that implements a function-like
136 // API. Additional variations, such as single-abstract-method classes with
137 // private constructors, or interfaces with multiple but related
138 // entry points, must be covered by hand-written or automatically
139 // generated adapter classes.
140 //
141 @CallerSensitive
142 public static
143 <T> T asInterfaceInstance(final Class<T> intfc, final MethodHandle target) {
144 if (!intfc.isInterface() || !Modifier.isPublic(intfc.getModifiers()))
145 throw new IllegalArgumentException("not a public interface: "+intfc.getName());
146 final MethodHandle mh;
147 if (System.getSecurityManager() != null) {
148 final Class<?> caller = Reflection.getCallerClass();
149 final ClassLoader ccl = caller != null ? caller.getClassLoader() : null;
150 ReflectUtil.checkProxyPackageAccess(ccl, intfc);
151 mh = ccl != null ? bindCaller(target, caller) : target;
152 } else {
153 mh = target;
154 }
155 ClassLoader proxyLoader = intfc.getClassLoader();
156 if (proxyLoader == null) {
157 ClassLoader cl = Thread.currentThread().getContextClassLoader(); // avoid use of BCP
158 proxyLoader = cl != null ? cl : ClassLoader.getSystemClassLoader();
159 }
160 final Method[] methods = getSingleNameMethods(intfc);
161 if (methods == null)
162 throw new IllegalArgumentException("not a single-method interface: "+intfc.getName());
163 final MethodHandle[] vaTargets = new MethodHandle[methods.length];
164 for (int i = 0; i < methods.length; i++) {
165 Method sm = methods[i];
166 MethodType smMT = MethodType.methodType(sm.getReturnType(), sm.getParameterTypes());
167 MethodHandle checkTarget = mh.asType(smMT); // make throw WMT
168 checkTarget = checkTarget.asType(checkTarget.type().changeReturnType(Object.class));
169 vaTargets[i] = checkTarget.asSpreader(Object[].class, smMT.parameterCount());
170 }
171 final InvocationHandler ih = new InvocationHandler() {
172 private Object getArg(String name) {
173 if ((Object)name == "getWrapperInstanceTarget") return target;
174 if ((Object)name == "getWrapperInstanceType") return intfc;
175 throw new AssertionError();
176 }
177 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
178 for (int i = 0; i < methods.length; i++) {
179 if (method.equals(methods[i]))
180 return vaTargets[i].invokeExact(args);
181 }
182 if (method.getDeclaringClass() == WrapperInstance.class)
183 return getArg(method.getName());
184 if (isObjectMethod(method))
185 return callObjectMethod(proxy, method, args);
186 throw new InternalError("bad proxy method: "+method);
187 }
188 };
189
190 final Object proxy;
191 if (System.getSecurityManager() != null) {
192 // sun.invoke.WrapperInstance is a restricted interface not accessible
193 // by any non-null class loader.
194 final ClassLoader loader = proxyLoader;
195 proxy = AccessController.doPrivileged(new PrivilegedAction<Object>() {
196 public Object run() {
197 return Proxy.newProxyInstance(
198 loader,
199 new Class<?>[]{ intfc, WrapperInstance.class },
200 ih);
201 }
202 });
203 } else {
204 proxy = Proxy.newProxyInstance(proxyLoader,
205 new Class<?>[]{ intfc, WrapperInstance.class },
206 ih);
207 }
208 return intfc.cast(proxy);
209 }
210
211 private static MethodHandle bindCaller(MethodHandle target, Class<?> hostClass) {
212 MethodHandle cbmh = MethodHandleImpl.bindCaller(target, hostClass);
213 if (target.isVarargsCollector()) {
214 MethodType type = cbmh.type();
215 int arity = type.parameterCount();
216 return cbmh.asVarargsCollector(type.parameterType(arity-1));
217 }
218 return cbmh;
219 }
220
221 /**
222 * Determines if the given object was produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
223 * @param x any reference
224 * @return true if the reference is not null and points to an object produced by {@code asInterfaceInstance}
225 */
226 public static
227 boolean isWrapperInstance(Object x) {
228 return x instanceof WrapperInstance;
229 }
230
231 private static WrapperInstance asWrapperInstance(Object x) {
232 try {
233 if (x != null)
234 return (WrapperInstance) x;
235 } catch (ClassCastException ex) {
236 }
237 throw new IllegalArgumentException("not a wrapper instance");
238 }
239
240 /**
241 * Produces or recovers a target method handle which is behaviorally
242 * equivalent to the unique method of this wrapper instance.
243 * The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
244 * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
245 * @param x any reference
246 * @return a method handle implementing the unique method
247 * @throws IllegalArgumentException if the reference x is not to a wrapper instance
248 */
249 public static
250 MethodHandle wrapperInstanceTarget(Object x) {
251 return asWrapperInstance(x).getWrapperInstanceTarget();
252 }
253
254 /**
255 * Recovers the unique single-method interface type for which this wrapper instance was created.
256 * The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
257 * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
258 * @param x any reference
259 * @return the single-method interface type for which the wrapper was created
260 * @throws IllegalArgumentException if the reference x is not to a wrapper instance
261 */
262 public static
263 Class<?> wrapperInstanceType(Object x) {
264 return asWrapperInstance(x).getWrapperInstanceType();
265 }
266
267 private static
268 boolean isObjectMethod(Method m) {
269 switch (m.getName()) {
270 case "toString":
271 return (m.getReturnType() == String.class
272 && m.getParameterTypes().length == 0);
273 case "hashCode":
274 return (m.getReturnType() == int.class
275 && m.getParameterTypes().length == 0);
276 case "equals":
277 return (m.getReturnType() == boolean.class
278 && m.getParameterTypes().length == 1
279 && m.getParameterTypes()[0] == Object.class);
280 }
281 return false;
282 }
283
284 private static
285 Object callObjectMethod(Object self, Method m, Object[] args) {
286 assert(isObjectMethod(m)) : m;
287 switch (m.getName()) {
288 case "toString":
289 return self.getClass().getName() + "@" + Integer.toHexString(self.hashCode());
290 case "hashCode":
291 return System.identityHashCode(self);
292 case "equals":
293 return (self == args[0]);
294 }
295 return null;
296 }
297
298 private static
299 Method[] getSingleNameMethods(Class<?> intfc) {
300 ArrayList<Method> methods = new ArrayList<Method>();
301 String uniqueName = null;
302 for (Method m : intfc.getMethods()) {
303 if (isObjectMethod(m)) continue;
304 if (!Modifier.isAbstract(m.getModifiers())) continue;
305 String mname = m.getName();
306 if (uniqueName == null)
307 uniqueName = mname;
308 else if (!uniqueName.equals(mname))
309 return null; // too many abstract methods
310 methods.add(m);
311 }
312 if (uniqueName == null) return null;
313 return methods.toArray(new Method[methods.size()]);
314 }
315 }