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}