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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.proxy.interceptor;
19  
20  import org.apache.commons.proxy.ObjectProvider;
21  import org.apache.commons.proxy.ProxyFactory;
22  import org.apache.commons.proxy.ProxyUtils;
23  import org.apache.commons.proxy.Interceptor;
24  
25  /**
26   * An <code>InterceptorChain</code> assists with creating proxies which go through a series of
27   * {@link Interceptor interceptors}.
28   *
29   * <pre>
30   *   MyServiceInterface serviceImpl = ...;
31   *   ProxyFactory factory = ...;
32   *   Interceptor[] interceptors = ...;
33   *   InterceptorChain chain = new InterceptorChain(interceptors);
34   *   ObjectProvider provider = chain.createProxyProvider(factory, serviceImpl);
35   *   MyServiceInterface serviceProxy = ( MyServiceInterface )provider.getObject();
36   *   serviceProxy.someServiceMethod(...); // This will go through the interceptors! 
37   * </pre>
38   *
39   * @author James Carman
40   * @since 1.0
41   */
42  public class InterceptorChain
43  {
44  //----------------------------------------------------------------------------------------------------------------------
45  // Fields
46  //----------------------------------------------------------------------------------------------------------------------
47      private final Interceptor[] interceptors;
48  
49  //----------------------------------------------------------------------------------------------------------------------
50  // Constructors
51  //----------------------------------------------------------------------------------------------------------------------
52  
53      public InterceptorChain( Interceptor[] interceptors )
54      {
55          this.interceptors = interceptors;
56      }
57  
58  //----------------------------------------------------------------------------------------------------------------------
59  // Other Methods
60  //----------------------------------------------------------------------------------------------------------------------
61  
62      private Object createProxy( ProxyFactory proxyFactory, ClassLoader classLoader, Object terminus,
63                                  Class[] proxyClasses )
64      {
65          Object currentTarget = terminus;
66          for( int i = interceptors.length - 1; i >= 0; --i )
67          {
68              currentTarget = proxyFactory
69                      .createInterceptorProxy( classLoader, currentTarget, interceptors[i], proxyClasses );
70          }
71          return currentTarget;
72      }
73  
74      /**
75       * Creates an {@link ObjectProvider} which will return a proxy that sends method invocations through this
76       * chain of interceptors and ultimately arrive at the supplied terminus object.  The proxy will support all
77       * interfaces implemented by the terminus object.  The thread context classloader will be used to generate the
78       * proxy class.
79       * 
80       * @param proxyFactory the {@link ProxyFactory} to use to create the proxy
81       * @param terminus the terminus
82       * @return an {@link ObjectProvider} which will return a proxy that sends method invocations through this
83       * chain of interceptors and ultimately arrive at the supplied terminus object
84       */
85      public ObjectProvider createProxyProvider( ProxyFactory proxyFactory, Object terminus )
86      {
87          return createProxyProvider( proxyFactory, terminus, null );
88      }
89  
90      /**
91       * Creates an {@link ObjectProvider} which will return a proxy that sends method invocations through this
92       * chain of interceptors and ultimately arrive at the supplied terminus object.  The proxy will support only
93       * the specified interfaces/classes.  The thread context classloader will be used to generate the
94       * proxy class.
95       *
96       * @param proxyFactory the {@link ProxyFactory} to use to create the proxy
97       * @param terminus the terminus
98       * @param proxyClasses the interfaces to support
99       * @return an {@link ObjectProvider} which will return a proxy that sends method invocations through this
100      * chain of interceptors and ultimately arrive at the supplied terminus object
101      */
102     public ObjectProvider createProxyProvider( ProxyFactory proxyFactory, Object terminus, Class[] proxyClasses )
103     {
104         return createProxyProvider( proxyFactory, Thread.currentThread().getContextClassLoader(), terminus,
105                                     proxyClasses );
106     }
107 
108     /**
109      * Creates an {@link ObjectProvider} which will return a proxy that sends method invocations through this
110      * chain of interceptors and ultimately arrive at the supplied terminus object.  The proxy will support only
111      * the specified interfaces/classes.  The specified classloader will be used to generate the
112      * proxy class.
113      *
114      * @param proxyFactory the {@link ProxyFactory} to use to create the proxy
115      * @param classLoader the classloader to be used to generate the proxy class
116      * @param terminus the terminus
117      * @param proxyClasses the interfaces to support
118      * @return an {@link ObjectProvider} which will return a proxy that sends method invocations through this
119      * chain of interceptors and ultimately arrive at the supplied terminus object
120      */
121     public ObjectProvider createProxyProvider( ProxyFactory proxyFactory, ClassLoader classLoader, Object terminus,
122                                                Class[] proxyClasses )
123     {
124         if( proxyClasses == null || proxyClasses.length == 0 )
125         {
126             proxyClasses = ProxyUtils.getAllInterfaces( terminus.getClass() );
127         }
128         return new ProxyObjectProvider( proxyFactory, classLoader, terminus, proxyClasses );
129     }
130 
131 //----------------------------------------------------------------------------------------------------------------------
132 // Inner Classes
133 //----------------------------------------------------------------------------------------------------------------------
134 
135     private class ProxyObjectProvider implements ObjectProvider
136     {
137         private final ClassLoader classLoader;
138         private final Class[] proxyClasses;
139         private final Object terminus;
140         private final ProxyFactory proxyFactory;
141 
142         public ProxyObjectProvider( ProxyFactory proxyFactory, ClassLoader classLoader, Object terminus,
143                                     Class[] proxyClasses )
144         {
145             this.classLoader = classLoader;
146             this.proxyClasses = proxyClasses;
147             this.terminus = terminus;
148             this.proxyFactory = proxyFactory;
149         }
150 
151         public Object getObject()
152         {
153             return createProxy( proxyFactory, classLoader, terminus, proxyClasses );
154         }
155     }
156 }
157