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1   package org.apache.velocity.app.event;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.    
20   */
21  
22  import org.apache.velocity.context.Context;
23  import org.apache.velocity.util.ContextAware;
24  
25  /**
26   *  Reference 'Stream insertion' event handler.  Called with object
27   *  that will be inserted into stream via value.toString().
28   *
29   *  Please return an Object that will toString() nicely :)
30   *
31   * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a>
32   * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
33   * @version $Id: ReferenceInsertionEventHandler.java 470256 2006-11-02 07:20:36Z wglass $
34   */
35  public interface  ReferenceInsertionEventHandler extends EventHandler
36  {
37      /**
38       * A call-back which is executed during Velocity merge before a reference
39       * value is inserted into the output stream. All registered
40       * ReferenceInsertionEventHandlers are called in sequence. If no
41       * ReferenceInsertionEventHandlers are are registered then reference value
42       * is inserted into the output stream as is.
43       *
44       * @param reference Reference from template about to be inserted.
45       * @param value Value about to be inserted (after its <code>toString()</code>
46       *            method is called).
47       * @return Object on which <code>toString()</code> should be called for
48       *         output.
49       */
50      public Object referenceInsert( String reference, Object value  );
51  
52      /**
53       * Defines the execution strategy for referenceInsert
54       */
55      static class referenceInsertExecutor implements EventHandlerMethodExecutor
56      {
57          private Context context;
58          private String reference;
59          private Object value;
60  
61          referenceInsertExecutor(
62                  Context context, 
63                  String reference, 
64                  Object value)
65          {
66              this.context = context;
67              this.reference = reference;
68              this.value = value;
69          }
70  
71          /**
72           * Call the method referenceInsert()
73           *  
74           * @param handler call the appropriate method on this handler
75           */
76          public void execute(EventHandler handler)
77          {
78              ReferenceInsertionEventHandler eh = (ReferenceInsertionEventHandler) handler;
79              
80              if (eh instanceof ContextAware)
81                  ((ContextAware) eh).setContext(context);
82  
83              /**
84               * Every successive call will alter the same value
85               */
86              value = ((ReferenceInsertionEventHandler) handler).referenceInsert(reference, value); 
87          }
88  
89          public Object getReturnValue()
90          {
91              return value;
92          }
93  
94          /**
95           * Continue to end of event handler iteration
96           * 
97           * @return always returns false
98           */
99          public boolean isDone()
100         {
101             return false;
102         }        
103     }
104 
105 }