Source for javax.management.openmbean.CompositeDataInvocationHandler

   1: /* CompositeDataInvocationHandler.java - Pseudo-accessors for CompositeData.
   2:    Copyright (C) 2007 Free Software Foundation
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package javax.management.openmbean;
  39: 
  40: import java.lang.reflect.InvocationHandler;
  41: import java.lang.reflect.Method;
  42: import java.lang.reflect.Proxy;
  43: 
  44: /**
  45:  * <p>
  46:  * Provides an {@link java.lang.reflect.InvocationHandler} which
  47:  * implements a series of accessor methods (those beginning with
  48:  * {@code "get"} or {@code "is"}) using the content of a
  49:  * {@link CompositeData} object.  An instance of {@link CompositeData}
  50:  * consists of a series of key-value mappings.  This handler assumes
  51:  * these keys to be the names of attributes, and thus provides
  52:  * accessor methods by returning the associated value.
  53:  * </p>
  54:  * <p>
  55:  * As an example, consider the following interface:
  56:  * </p>
  57:  * <pre>
  58:  * public interface Person
  59:  * {
  60:  *   public String getName();
  61:  *   public Date getBirthday();
  62:  * }
  63:  * </pre>
  64:  * <p>
  65:  * This specifies two accessor methods for retrieving the attributes,
  66:  * {@code name} and {@code birthday}.  An implementation of this interface
  67:  * can be provided by creating an instance of this class, using a
  68:  * {@link CompositeData} object with appropriate key-value mappings
  69:  * (e.g. "name" => "Fred", "birthday" => 30/06/1974), and then passing
  70:  * that to {@link java.lang.reflect.Proxy#newProxyInstance} along with
  71:  * the interface itself.  The invocation handler implements the methods
  72:  * by calling {@link CompositeData#get(String)} with the appropriate key.
  73:  * </p>
  74:  * <p>
  75:  * The attribute name is derived by taking the remainder of the method
  76:  * name following {@code "get"}.  If the first letter of this substring
  77:  * is uppercase, then two attempts are made to retrieve the attribute
  78:  * from the {@link CompositeData} instance: one using the original substring,
  79:  * and one with the first letter changed to its lower-case equivalent.
  80:  * If the first letter is lowercase, only the exact substring is used.
  81:  * </p>
  82:  * <p>
  83:  * An {@link Object#equals(Object)} implementation is provided.  This returns
  84:  * true if the argument is a proxy with a {@link CompositeDataInvocationHandler}
  85:  * using an equivalent {@link CompositeData} instance.  {@link Object#hashCode()}
  86:  * is also defined so as to match this implementation and give equivalent instances
  87:  * the same hashcode.
  88:  * </p>
  89:  *
  90:  * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
  91:  * @since 1.6
  92:  */
  93: public class CompositeDataInvocationHandler
  94:   implements InvocationHandler
  95: {
  96: 
  97:   /**
  98:    * The {@link CompositeData} providing the key-value mappings.
  99:    */
 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: }