001/* CompositeDataInvocationHandler.java - Pseudo-accessors for CompositeData. 002 Copyright (C) 2007 Free Software Foundation 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038package javax.management.openmbean; 039 040import java.lang.reflect.InvocationHandler; 041import java.lang.reflect.Method; 042import java.lang.reflect.Proxy; 043 044/** 045 * <p> 046 * Provides an {@link java.lang.reflect.InvocationHandler} which 047 * implements a series of accessor methods (those beginning with 048 * {@code "get"} or {@code "is"}) using the content of a 049 * {@link CompositeData} object. An instance of {@link CompositeData} 050 * consists of a series of key-value mappings. This handler assumes 051 * these keys to be the names of attributes, and thus provides 052 * accessor methods by returning the associated value. 053 * </p> 054 * <p> 055 * As an example, consider the following interface: 056 * </p> 057 * <pre> 058 * public interface Person 059 * { 060 * public String getName(); 061 * public Date getBirthday(); 062 * } 063 * </pre> 064 * <p> 065 * This specifies two accessor methods for retrieving the attributes, 066 * {@code name} and {@code birthday}. An implementation of this interface 067 * can be provided by creating an instance of this class, using a 068 * {@link CompositeData} object with appropriate key-value mappings 069 * (e.g. "name" => "Fred", "birthday" => 30/06/1974), and then passing 070 * that to {@link java.lang.reflect.Proxy#newProxyInstance} along with 071 * the interface itself. The invocation handler implements the methods 072 * by calling {@link CompositeData#get(String)} with the appropriate key. 073 * </p> 074 * <p> 075 * The attribute name is derived by taking the remainder of the method 076 * name following {@code "get"}. If the first letter of this substring 077 * is uppercase, then two attempts are made to retrieve the attribute 078 * from the {@link CompositeData} instance: one using the original substring, 079 * and one with the first letter changed to its lower-case equivalent. 080 * If the first letter is lowercase, only the exact substring is used. 081 * </p> 082 * <p> 083 * An {@link Object#equals(Object)} implementation is provided. This returns 084 * true if the argument is a proxy with a {@link CompositeDataInvocationHandler} 085 * using an equivalent {@link CompositeData} instance. {@link Object#hashCode()} 086 * is also defined so as to match this implementation and give equivalent instances 087 * the same hashcode. 088 * </p> 089 * 090 * @author Andrew John Hughes (gnu_andrew@member.fsf.org) 091 * @since 1.6 092 */ 093public class CompositeDataInvocationHandler 094 implements InvocationHandler 095{ 096 097 /** 098 * The {@link CompositeData} providing the key-value mappings. 099 */ 100 private CompositeData data; 101 102 /** 103 * Constructs a new {@link CompositeDataInvocationHandler} 104 * with the specified {@link CompositeData} instance. 105 * 106 * @param data the {@link CompositeData} instance to use. 107 * @throws IllegalArgumentException if {@code data} is {@code null}. 108 */ 109 public CompositeDataInvocationHandler(CompositeData data) 110 { 111 if (data == null) 112 throw new IllegalArgumentException("The CompositeData instance " + 113 "must be non-null."); 114 this.data = data; 115 } 116 117 /** 118 * Returns the {@link CompositeData} instance which provides 119 * the key-value mappings for this instance. This is never 120 * {@code null}. 121 * 122 * @return the {@link CompositeData} instance. 123 */ 124 public CompositeData getCompositeData() 125 { 126 return data; 127 } 128 129 /** 130 * Called by the proxy class whenever a method is called. The 131 * handler only deals with accessor methods (beginning with 132 * {@code "get"} or {@code "is"}), {@code equals}, and 133 * {@code "hashCode"}. Accessor methods are implemented by 134 * returning the appropriate value from the {@link CompositeData} 135 * instance, while {@code equals} and {@code hashCode} allow 136 * two proxies with a {@link CompositeDataInvocationHandler} using 137 * the same {@link CompositeData} instance to be classified 138 * as equivalent. 139 * 140 * @param proxy the proxy on which the method was called. 141 * @param method the method which was called. 142 * @param args the arguments supplied to the method. 143 * @return the return value from the method. 144 * @throws Throwable if an exception is thrown in the process. 145 */ 146 public Object invoke(Object proxy, Method method, Object[] args) 147 throws Throwable 148 { 149 String mName = method.getName(); 150 if (mName.equals("equals")) 151 { 152 if (args[0] instanceof Proxy) 153 { 154 InvocationHandler h = Proxy.getInvocationHandler(args[0]); 155 if (h instanceof CompositeDataInvocationHandler) 156 return data.equals(((CompositeDataInvocationHandler) 157 h).getCompositeData()); 158 } 159 return false; 160 } 161 if (mName.equals("hashCode")) 162 { 163 return data.hashCode(); 164 } 165 String attrib = null; 166 if (mName.startsWith("get")) 167 attrib = mName.substring(3); 168 else if (mName.startsWith("is")) 169 attrib = mName.substring(2); 170 if (attrib == null) 171 throw new NoSuchMethodException(mName + " is not an accessor."); 172 if (!data.containsKey(attrib)) 173 { 174 if (Character.isLowerCase(attrib.charAt(0))) 175 throw new NoSuchMethodException("The attribute " + 176 attrib + " is not available " + 177 "in the given CompositeData " + 178 "object"); 179 attrib = Character.toLowerCase(attrib.charAt(0)) 180 + attrib.substring(1); 181 if (!data.containsKey(attrib)) 182 throw new NoSuchMethodException("The attribute " + 183 attrib + " is not available " + 184 "in the given CompositeData " + 185 "object"); 186 } 187 return data.get(attrib); 188 } 189 190}