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1   /*
2    * ====================================================================
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *   http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing,
14   * software distributed under the License is distributed on an
15   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16   * KIND, either express or implied.  See the License for the
17   * specific language governing permissions and limitations
18   * under the License.
19   * ====================================================================
20   *
21   * This software consists of voluntary contributions made by many
22   * individuals on behalf of the Apache Software Foundation.  For more
23   * information on the Apache Software Foundation, please see
24   * <http://www.apache.org/>.
25   *
26   */
27  
28  package org.apache.http.protocol;
29  
30  import java.util.Collection;
31  import java.util.HashMap;
32  import java.util.LinkedList;
33  import java.util.Map;
34  
35  import org.apache.http.annotation.NotThreadSafe;
36  
37  /**
38   * Builder class to build a linked list (chain) of unique class instances. Each class can have
39   * only one instance in the list. Useful for building lists of protocol interceptors.
40   *
41   * @see ImmutableHttpProcessor
42   *
43   * @since 4.3
44   */
45  @NotThreadSafe
46  final class ChainBuilder<E> {
47  
48      private final LinkedList<E> list;
49      private final Map<Class<?>, E> uniqueClasses;
50  
51      public ChainBuilder() {
52          this.list = new LinkedList<E>();
53          this.uniqueClasses = new HashMap<Class<?>, E>();
54      }
55  
56      private void ensureUnique(final E e) {
57          final E previous = this.uniqueClasses.remove(e.getClass());
58          if (previous != null) {
59              this.list.remove(previous);
60          }
61          this.uniqueClasses.put(e.getClass(), e);
62      }
63  
64      public ChainBuilder<E> addFirst(final E e) {
65          if (e == null) {
66              return this;
67          }
68          ensureUnique(e);
69          this.list.addFirst(e);
70          return this;
71      }
72  
73      public ChainBuilder<E> addLast(final E e) {
74          if (e == null) {
75              return this;
76          }
77          ensureUnique(e);
78          this.list.addLast(e);
79          return this;
80      }
81  
82      public ChainBuilder<E> addAllFirst(final Collection<E> c) {
83          if (c == null) {
84              return this;
85          }
86          for (final E e: c) {
87              addFirst(e);
88          }
89          return this;
90      }
91  
92      public ChainBuilder<E> addAllFirst(final E... c) {
93          if (c == null) {
94              return this;
95          }
96          for (final E e: c) {
97              addFirst(e);
98          }
99          return this;
100     }
101 
102     public ChainBuilder<E> addAllLast(final Collection<E> c) {
103         if (c == null) {
104             return this;
105         }
106         for (final E e: c) {
107             addLast(e);
108         }
109         return this;
110     }
111 
112     public ChainBuilder<E> addAllLast(final E... c) {
113         if (c == null) {
114             return this;
115         }
116         for (final E e: c) {
117             addLast(e);
118         }
119         return this;
120     }
121 
122     public LinkedList<E> build() {
123         return new LinkedList<E>(this.list);
124     }
125 
126 }