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1   package org.apache.velocity.app.event;
2   
3   import org.apache.velocity.context.Context;
4   import org.apache.velocity.util.ContextAware;
5   
6   /*
7    * Licensed to the Apache Software Foundation (ASF) under one
8    * or more contributor license agreements.  See the NOTICE file
9    * distributed with this work for additional information
10   * regarding copyright ownership.  The ASF licenses this file
11   * to you under the Apache License, Version 2.0 (the
12   * "License"); you may not use this file except in compliance
13   * with the License.  You may obtain a copy of the License at
14   *
15   *   http://www.apache.org/licenses/LICENSE-2.0
16   *
17   * Unless required by applicable law or agreed to in writing,
18   * software distributed under the License is distributed on an
19   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
20   * KIND, either express or implied.  See the License for the
21   * specific language governing permissions and limitations
22   * under the License.    
23   */
24  
25  /**
26   *  Event handler called when a method throws an exception.  This gives the
27   *  application a chance to deal with it and either
28   *  return something nice, or throw.
29   *
30   *  Please return what you want rendered into the output stream.
31   *
32   * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a>
33   * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
34   * @version $Id: MethodExceptionEventHandler.java 470256 2006-11-02 07:20:36Z wglass $
35   */
36  public interface MethodExceptionEventHandler extends EventHandler
37  {
38      /**
39       * Called when a method throws an exception.
40       * Only the first registered MethodExceptionEventHandler is called.  If
41       * none are registered a MethodInvocationException is thrown.
42       *
43       * @param claz the class of the object the method is being applied to
44       * @param method the method
45       * @param e the thrown exception
46       * @return an object to insert in the page
47       * @throws Exception an exception to be thrown instead inserting an object
48       */
49      public Object methodException( Class claz, String method, Exception e )
50           throws Exception;
51  
52      /**
53       * Defines the execution strategy for methodException
54       */
55      static class MethodExceptionExecutor implements EventHandlerMethodExecutor
56      {
57          private Context context;
58          private Class claz;
59          private String method;
60          private Exception e;
61          
62          private Object result;
63          private boolean executed = false;
64      
65          MethodExceptionExecutor(
66                  Context context, 
67                  Class claz,
68                  String method,
69                  Exception e)
70          {
71              this.context = context;
72              this.claz = claz;
73              this.method = method;
74              this.e = e;
75          }
76  
77          /**
78           * Call the method methodException()
79           *  
80           * @param handler call the appropriate method on this handler
81           * @exception Exception generic exception thrown by methodException event handler method call
82           */
83          public void execute(EventHandler handler) throws Exception
84          {
85              MethodExceptionEventHandler eh = (MethodExceptionEventHandler) handler;
86              
87              if (eh instanceof ContextAware)
88                  ((ContextAware) eh).setContext(context);
89  
90              executed = true;
91              result = ((MethodExceptionEventHandler) handler).methodException(claz, method, e);
92          }
93  
94          public Object getReturnValue()
95          {
96              return result;
97          }
98  
99          /**
100          * Only run the first MethodExceptionEventHandler
101          * 
102          * @return true after this is executed once.
103          */
104         public boolean isDone()
105         {
106            return executed;
107         }        
108         
109         
110     }
111 
112 }