| /* | |
| * Copyright (c) 1999, 2024, Oracle and/or its affiliates. All rights reserved. | |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| * | |
| * This code is free software; you can redistribute it and/or modify it | |
| * under the terms of the GNU General Public License version 2 only, as | |
| * published by the Free Software Foundation. Oracle designates this | |
| * particular file as subject to the "Classpath" exception as provided | |
| * by Oracle in the LICENSE file that accompanied this code. | |
| * | |
| * This code is distributed in the hope that it will be useful, but WITHOUT | |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| * version 2 for more details (a copy is included in the LICENSE file that | |
| * accompanied this code). | |
| * | |
| * You should have received a copy of the GNU General Public License version | |
| * 2 along with this work; if not, write to the Free Software Foundation, | |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| * | |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| * or visit www.oracle.com if you need additional information or have any | |
| * questions. | |
| */ | |
| package java.lang.reflect; | |
| import jdk.internal.reflect.CallerSensitive; | |
| import jdk.internal.reflect.Reflection; | |
| import java.util.Objects; | |
| /** | |
| * {@code InvocationHandler} is the interface implemented by | |
| * the <i>invocation handler</i> of a proxy instance. | |
| * | |
| * <p>Each proxy instance has an associated invocation handler. | |
| * When a method is invoked on a proxy instance, the method | |
| * invocation is encoded and dispatched to the {@code invoke} | |
| * method of its invocation handler. | |
| * | |
| * @author Peter Jones | |
| * @see Proxy | |
| * @since 1.3 | |
| */ | |
| public interface InvocationHandler { | |
| /** | |
| * Processes a method invocation on a proxy instance and returns | |
| * the result. This method will be invoked on an invocation handler | |
| * when a method is invoked on a proxy instance that it is | |
| * associated with. | |
| * | |
| * @param proxy the proxy instance that the method was invoked on | |
| * | |
| * @param method the {@code Method} instance corresponding to | |
| * the interface method invoked on the proxy instance. The declaring | |
| * class of the {@code Method} object will be the interface that | |
| * the method was declared in, which may be a superinterface of the | |
| * proxy interface that the proxy class inherits the method through. | |
| * | |
| * @param args an array of objects containing the values of the | |
| * arguments passed in the method invocation on the proxy instance, | |
| * or {@code null} if interface method takes no arguments. | |
| * Arguments of primitive types are wrapped in instances of the | |
| * appropriate primitive wrapper class, such as | |
| * {@code java.lang.Integer} or {@code java.lang.Boolean}. | |
| * | |
| * @return the value to return from the method invocation on the | |
| * proxy instance. If the declared return type of the interface | |
| * method is a primitive type, then the value returned by | |
| * this method must be an instance of the corresponding primitive | |
| * wrapper class; otherwise, it must be a type assignable to the | |
| * declared return type. If the value returned by this method is | |
| * {@code null} and the interface method's return type is | |
| * primitive, then a {@code NullPointerException} will be | |
| * thrown by the method invocation on the proxy instance. If the | |
| * value returned by this method is otherwise not compatible with | |
| * the interface method's declared return type as described above, | |
| * a {@code ClassCastException} will be thrown by the method | |
| * invocation on the proxy instance. | |
| * | |
| * @throws Throwable the exception to throw from the method | |
| * invocation on the proxy instance. The exception's type must be | |
| * assignable either to any of the exception types declared in the | |
| * {@code throws} clause of the interface method or to the | |
| * unchecked exception types {@code java.lang.RuntimeException} | |
| * or {@code java.lang.Error}. If a checked exception is | |
| * thrown by this method that is not assignable to any of the | |
| * exception types declared in the {@code throws} clause of | |
| * the interface method, then an | |
| * {@link UndeclaredThrowableException} containing the | |
| * exception that was thrown by this method will be thrown by the | |
| * method invocation on the proxy instance. | |
| * | |
| * @see UndeclaredThrowableException | |
| */ | |
| public Object invoke(Object proxy, Method method, Object[] args) | |
| throws Throwable; | |
| /** | |
| * Invokes the specified default method on the given {@code proxy} instance with | |
| * the given parameters. The given {@code method} must be a default method | |
| * declared in a proxy interface of the {@code proxy}'s class or inherited | |
| * from its superinterface directly or indirectly. | |
| * <p> | |
| * Invoking this method behaves as if {@code invokespecial} instruction executed | |
| * from the proxy class, targeting the default method in a proxy interface. | |
| * This is equivalent to the invocation: | |
| * {@code X.super.m(A* a)} where {@code X} is a proxy interface and the call to | |
| * {@code X.super::m(A*)} is resolved to the given {@code method}. | |
| * <p> | |
| * Examples: interface {@code A} and {@code B} both declare a default | |
| * implementation of method {@code m}. Interface {@code C} extends {@code A} | |
| * and inherits the default method {@code m} from its superinterface {@code A}. | |
| * | |
| * <blockquote><pre>{@code | |
| * interface A { | |
| * default T m(A a) { return t1; } | |
| * } | |
| * interface B { | |
| * default T m(A a) { return t2; } | |
| * } | |
| * interface C extends A {} | |
| * }</pre></blockquote> | |
| * | |
| * The following creates a proxy instance that implements {@code A} | |
| * and invokes the default method {@code A::m}. | |
| * | |
| * <blockquote><pre>{@code | |
| * Object proxy = Proxy.newProxyInstance(loader, new Class<?>[] { A.class }, | |
| * (o, m, params) -> { | |
| * if (m.isDefault()) { | |
| * // if it's a default method, invoke it | |
| * return InvocationHandler.invokeDefault(o, m, params); | |
| * } | |
| * }); | |
| * }</pre></blockquote> | |
| * | |
| * If a proxy instance implements both {@code A} and {@code B}, both | |
| * of which provides the default implementation of method {@code m}, | |
| * the invocation handler can dispatch the method invocation to | |
| * {@code A::m} or {@code B::m} via the {@code invokeDefault} method. | |
| * For example, the following code delegates the method invocation | |
| * to {@code B::m}. | |
| * | |
| * <blockquote><pre>{@code | |
| * Object proxy = Proxy.newProxyInstance(loader, new Class<?>[] { A.class, B.class }, | |
| * (o, m, params) -> { | |
| * if (m.getName().equals("m")) { | |
| * // invoke B::m instead of A::m | |
| * Method bMethod = B.class.getMethod(m.getName(), m.getParameterTypes()); | |
| * return InvocationHandler.invokeDefault(o, bMethod, params); | |
| * } | |
| * }); | |
| * }</pre></blockquote> | |
| * | |
| * If a proxy instance implements {@code C} that inherits the default | |
| * method {@code m} from its superinterface {@code A}, then | |
| * the interface method invocation on {@code "m"} is dispatched to | |
| * the invocation handler's {@link #invoke(Object, Method, Object[]) invoke} | |
| * method with the {@code Method} object argument representing the | |
| * default method {@code A::m}. | |
| * | |
| * <blockquote><pre>{@code | |
| * Object proxy = Proxy.newProxyInstance(loader, new Class<?>[] { C.class }, | |
| * (o, m, params) -> { | |
| * if (m.isDefault()) { | |
| * // behaves as if calling C.super.m(params) | |
| * return InvocationHandler.invokeDefault(o, m, params); | |
| * } | |
| * }); | |
| * }</pre></blockquote> | |
| * | |
| * The invocation of method {@code "m"} on this {@code proxy} will behave | |
| * as if {@code C.super::m} is called and that is resolved to invoking | |
| * {@code A::m}. | |
| * <p> | |
| * Adding a default method, or changing a method from abstract to default | |
| * may cause an exception if an existing code attempts to call {@code invokeDefault} | |
| * to invoke a default method. | |
| * | |
| * For example, if {@code C} is modified to implement a default method | |
| * {@code m}: | |
| * | |
| * <blockquote><pre>{@code | |
| * interface C extends A { | |
| * default T m(A a) { return t3; } | |
| * } | |
| * }</pre></blockquote> | |
| * | |
| * The code above that creates proxy instance {@code proxy} with | |
| * the modified {@code C} will run with no exception and it will result in | |
| * calling {@code C::m} instead of {@code A::m}. | |
| * <p> | |
| * The following is another example that creates a proxy instance of {@code C} | |
| * and the invocation handler calls the {@code invokeDefault} method | |
| * to invoke {@code A::m}: | |
| * | |
| * <blockquote><pre>{@code | |
| * C c = (C) Proxy.newProxyInstance(loader, new Class<?>[] { C.class }, | |
| * (o, m, params) -> { | |
| * if (m.getName().equals("m")) { | |
| * // IllegalArgumentException thrown as {@code A::m} is not a method | |
| * // inherited from its proxy interface C | |
| * Method aMethod = A.class.getMethod(m.getName(), m.getParameterTypes()); | |
| * return InvocationHandler.invokeDefault(o, aMethod params); | |
| * } | |
| * }); | |
| * c.m(...); | |
| * }</pre></blockquote> | |
| * | |
| * The above code runs successfully with the old version of {@code C} and | |
| * {@code A::m} is invoked. When running with the new version of {@code C}, | |
| * the above code will fail with {@code IllegalArgumentException} because | |
| * {@code C} overrides the implementation of the same method and | |
| * {@code A::m} is not accessible by a proxy instance. | |
| * | |
| * @apiNote | |
| * The {@code proxy} parameter is of type {@code Object} rather than {@code Proxy} | |
| * to make it easy for {@link InvocationHandler#invoke(Object, Method, Object[]) | |
| * InvocationHandler::invoke} implementation to call directly without the need | |
| * of casting. | |
| * | |
| * @param proxy the {@code Proxy} instance on which the default method to be invoked | |
| * @param method the {@code Method} instance corresponding to a default method | |
| * declared in a proxy interface of the proxy class or inherited | |
| * from its superinterface directly or indirectly | |
| * @param args the parameters used for the method invocation; can be {@code null} | |
| * if the number of formal parameters required by the method is zero. | |
| * @return the value returned from the method invocation | |
| * | |
| * @throws IllegalArgumentException if any of the following conditions is {@code true}: | |
| * <ul> | |
| * <li>{@code proxy} is not {@linkplain Proxy#isProxyClass(Class) | |
| * a proxy instance}; or</li> | |
| * <li>the given {@code method} is not a default method declared | |
| * in a proxy interface of the proxy class and not inherited from | |
| * any of its superinterfaces; or</li> | |
| * <li>the given {@code method} is overridden directly or indirectly by | |
| * the proxy interfaces and the method reference to the named | |
| * method never resolves to the given {@code method}; or</li> | |
| * <li>the length of the given {@code args} array does not match the | |
| * number of parameters of the method to be invoked; or</li> | |
| * <li>any of the {@code args} elements fails the unboxing | |
| * conversion if the corresponding method parameter type is | |
| * a primitive type; or if, after possible unboxing, any of the | |
| * {@code args} elements cannot be assigned to the corresponding | |
| * method parameter type.</li> | |
| * </ul> | |
| * @throws IllegalAccessException if the declaring class of the specified | |
| * default method is inaccessible to the caller class | |
| * @throws NullPointerException if {@code proxy} or {@code method} is {@code null} | |
| * @throws Throwable anything thrown by the default method | |
| * @since 16 | |
| * @jvms 5.4.3 Resolution | |
| */ | |
| @CallerSensitive | |
| public static Object invokeDefault(Object proxy, Method method, Object... args) | |
| throws Throwable { | |
| Objects.requireNonNull(proxy); | |
| Objects.requireNonNull(method); | |
| return Proxy.invokeDefault(proxy, method, args, Reflection.getCallerClass()); | |
| } | |
| } |