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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 the RHS of #set is null.  Lets an app approve / veto
27   *  writing a log message based on the specific reference.
28   *
29   * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a>
30   * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
31   * @version $Id: NullSetEventHandler.java 470256 2006-11-02 07:20:36Z wglass $
32   */
33  public interface NullSetEventHandler extends EventHandler
34  {
35      /**
36       * Called when the RHS of a #set() is null, which will result
37       * in a null LHS. All NullSetEventHandlers
38       * are called in sequence until a false is returned.  If no NullSetEventHandler
39       * is registered all nulls will be logged.
40       *
41       *  @param lhs  reference literal of left-hand-side of set statement
42       *  @param rhs  reference literal of right-hand-side of set statement
43       *  @return true if log message should be written, false otherwise
44       */
45      public boolean shouldLogOnNullSet( String lhs, String rhs );
46  
47      /**
48       * Defines the execution strategy for shouldLogOnNullSet
49       */
50      static class ShouldLogOnNullSetExecutor implements EventHandlerMethodExecutor
51      {
52          private Context context;
53          private String lhs;
54          private String rhs;
55  
56          /**
57           * when this is false, quit iterating
58           */
59          private boolean result = true;
60          private boolean executed = false;
61          
62          ShouldLogOnNullSetExecutor(
63                  Context context, 
64                  String lhs, 
65                  String rhs) 
66          {
67              this.context = context;
68              this.lhs = lhs;
69              this.rhs = rhs;
70          }
71  
72          /**
73           * Call the method shouldLogOnNullSet()
74           *  
75           * @param handler call the appropriate method on this handler
76           */
77          public void execute(EventHandler handler)
78          {
79              NullSetEventHandler eh = (NullSetEventHandler) handler;
80              
81              if (eh instanceof ContextAware)
82                  ((ContextAware) eh).setContext(context);
83  
84              executed = true;
85              result = ((NullSetEventHandler) handler).shouldLogOnNullSet(lhs, rhs); 
86          }
87  
88          public Object getReturnValue()
89          {            
90              return new Boolean(result);
91          }
92  
93          public boolean isDone()
94          {
95              return executed && !result;
96          }        
97          
98          
99      }
100 
101 }