1/* 2 * Copyright (c) 2015, 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 26package jdk.dynalink.beans; 27 28import java.lang.invoke.MethodHandle; 29import jdk.dynalink.DynamicLinkerFactory; 30import jdk.dynalink.NamedOperation; 31import jdk.dynalink.NoSuchDynamicMethodException; 32import jdk.dynalink.StandardOperation; 33import jdk.dynalink.linker.LinkRequest; 34import jdk.dynalink.linker.LinkerServices; 35 36/** 37 * A factory for creating method handles for linking missing member behavior 38 * in {@link BeansLinker}. BeansLinker links these method handles into guarded 39 * invocations for link requests specifying {@code GET_*} and {@code SET_*} 40 * {@link StandardOperation}s when it is either certain or possible that the 41 * requested member (property, method, or element) is missing. They will be 42 * linked both for {@link NamedOperation named} and unnamed operations. The 43 * implementer must ensure that the parameter types of the returned method 44 * handle match the parameter types of the call site described in the link 45 * request. The return types can differ, though, to allow 46 * {@link DynamicLinkerFactory#setPrelinkTransformer(jdk.dynalink.linker.GuardedInvocationTransformer)} 47 * late return type transformations}. It is allowed to return {@code null} for a 48 * method handle if the default behavior is sufficient. 49 * <h2>Default missing member behavior</h2> 50 * When a {@link BeansLinker} is configured without a missing member handler 51 * factory, or the factory returns {@code null} for a particular handler 52 * creation invocation, the default behavior is used. The default behavior is to 53 * return {@code null} from 54 * {@link BeansLinker#getGuardedInvocation(LinkRequest, LinkerServices)} when it 55 * can be determined at link time that the linked operation will never address 56 * an existing member. This lets the {@code DynamicLinker} attempt the next 57 * linker if there is one, or ultimately fail the link request with 58 * {@link NoSuchDynamicMethodException}. For other cases (typically all unnamed 59 * member operations as well as most named operations on collection elements) 60 * {@code BeansLinker} will produce a conditional linkage that will return 61 * {@code null} when invoked at runtime with a name that does not match any 62 * member for getters and silently ignore the passed values for setters. 63 * <h2>Implementing exception-throwing behavior</h2> 64 * Note that if the language-specific behavior for an operation on a missing 65 * member is to throw an exception then the factory should produce a method 66 * handle that throws the exception when invoked, and must not throw an 67 * exception itself, as the linkage for the missing member is often conditional. 68 * 69 * @see BeansLinker#BeansLinker(MissingMemberHandlerFactory) 70 */ 71@FunctionalInterface 72public interface MissingMemberHandlerFactory { 73 /** 74 * Returns a method handle suitable for implementing missing member behavior 75 * for a particular link request. See the class description for details. 76 * @param linkRequest the current link request 77 * @param linkerServices the current link services 78 * @return a method handle that can be invoked if the property, element, or 79 * method being addressed by an operation is missing. The return value can 80 * be null. 81 * @throws Exception if the operation fails for any reason. Please observe 82 * the class documentation notes for implementing exception-throwing 83 * missing member behavior. 84 */ 85 public MethodHandle createMissingMemberHandler(LinkRequest linkRequest, LinkerServices linkerServices) throws Exception; 86} 87