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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  /** 
23   * Strategy object used to execute event handler method.  Will be called
24   * while looping through all the chained event handler implementations.
25   * Each EventHandler method call should have a parallel executor object
26   * defined.  
27   *
28   * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a>
29   * @version $Id: EventHandlerMethodExecutor.java 470256 2006-11-02 07:20:36Z wglass $
30   */
31  public interface EventHandlerMethodExecutor
32  {
33      /**
34       * Execute the event handler method.  If Object is not null, do not 
35       * iterate further through the handler chain.
36       * If appropriate, the returned Object will be the return value.
37       *  
38       * @param handler call the appropriate method on this handler
39       * @exception Exception generic exception potentially thrown by event handlers
40       */
41      public void execute(EventHandler handler) throws Exception;
42  
43      /**
44       * Called after execute() to see if iterating should stop. Should
45       * always return false before method execute() is run.
46       * 
47       * @return true if no more event handlers for this method should be called.
48       */
49      public boolean isDone();
50  
51      /**
52       * Get return value at end of all the iterations
53       * 
54       * @return null if no return value is required
55       */
56      public Object getReturnValue();
57  }