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1   /*
2    * $Id: MergeIteratorFilter.java 471756 2006-11-06 15:01:43Z husted $
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  package org.apache.struts2.util;
22  
23  import java.util.ArrayList;
24  import java.util.Iterator;
25  import java.util.List;
26  
27  import com.opensymphony.xwork2.Action;
28  
29  
30  /***
31   * A bean that takes several iterators and outputs the merge of them. Used by
32   * MergeIteratorTag.
33   *
34   * @see org.apache.struts2.views.jsp.iterator.MergeIteratorTag
35   * @see org.apache.struts2.components.MergeIterator
36   */
37  public class MergeIteratorFilter extends IteratorFilterSupport implements Iterator, Action {
38  
39      List iterators = new ArrayList();
40  
41      // Attributes ----------------------------------------------------
42      List sources = new ArrayList();
43      int idx = 0;
44  
45  
46      // Public --------------------------------------------------------
47      public void setSource(Object anIterator) {
48          sources.add(anIterator);
49      }
50  
51      // Action implementation -----------------------------------------
52      public String execute() {
53          // Make source transformations
54          for (int i = 0; i < sources.size(); i++) {
55              Object source = sources.get(i);
56              iterators.add(getIterator(source));
57          }
58  
59          return SUCCESS;
60      }
61  
62      // Iterator implementation ---------------------------------------
63      public boolean hasNext() {
64          while (iterators.size() > 0) {
65              if (((Iterator) iterators.get(idx)).hasNext()) {
66                  return true;
67              } else {
68                  iterators.remove(idx);
69  
70                  if (iterators.size() > 0) {
71                      idx = idx % iterators.size();
72                  }
73              }
74          }
75  
76          return false;
77      }
78  
79      public Object next() {
80          try {
81              return ((Iterator) iterators.get(idx)).next();
82          } finally {
83              idx = (idx + 1) % iterators.size();
84          }
85      }
86  
87      public void remove() {
88          throw new UnsupportedOperationException("Remove is not supported in MergeIteratorFilter.");
89      }
90  }