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1   /*
2    * $Id: MergeIteratorFilter.java 439747 2006-09-03 09:22:46Z mrdon $
3    *
4    * Copyright 2006 The Apache Software Foundation.
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    *
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.struts2.util;
19  
20  import java.util.ArrayList;
21  import java.util.Iterator;
22  import java.util.List;
23  
24  import com.opensymphony.xwork2.Action;
25  
26  
27  /***
28   * A bean that takes several iterators and outputs the merge of them. Used by 
29   * MergeIteratorTag.
30   *
31   * @see org.apache.struts2.views.jsp.iterator.MergeIteratorTag
32   * @see org.apache.struts2.components.MergeIterator
33   */
34  public class MergeIteratorFilter extends IteratorFilterSupport implements Iterator, Action {
35  
36      List iterators = new ArrayList();
37  
38      // Attributes ----------------------------------------------------
39      List sources = new ArrayList();
40      int idx = 0;
41  
42  
43      // Public --------------------------------------------------------
44      public void setSource(Object anIterator) {
45          sources.add(anIterator);
46      }
47  
48      // Action implementation -----------------------------------------
49      public String execute() {
50          // Make source transformations
51          for (int i = 0; i < sources.size(); i++) {
52              Object source = sources.get(i);
53              iterators.add(getIterator(source));
54          }
55  
56          return SUCCESS;
57      }
58  
59      // Iterator implementation ---------------------------------------
60      public boolean hasNext() {
61          while (iterators.size() > 0) {
62              if (((Iterator) iterators.get(idx)).hasNext()) {
63                  return true;
64              } else {
65                  iterators.remove(idx);
66  
67                  if (iterators.size() > 0) {
68                      idx = idx % iterators.size();
69                  }
70              }
71          }
72  
73          return false;
74      }
75  
76      public Object next() {
77          try {
78              return ((Iterator) iterators.get(idx)).next();
79          } finally {
80              idx = (idx + 1) % iterators.size();
81          }
82      }
83  
84      public void remove() {
85          throw new UnsupportedOperationException("Remove is not supported in MergeIteratorFilter.");
86      }
87  }