001 /* CompositeDataInvocationHandler.java - Pseudo-accessors for CompositeData.
002 Copyright (C) 2007 Free Software Foundation
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package javax.management.openmbean;
039
040 import java.lang.reflect.InvocationHandler;
041 import java.lang.reflect.Method;
042 import 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 */
093 public 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 }