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.message;
29
30 import java.util.List;
31 import java.util.NoSuchElementException;
32
33 import org.apache.http.Header;
34 import org.apache.http.HeaderIterator;
35 import org.apache.http.util.Args;
36 import org.apache.http.util.Asserts;
37
38 /**
39 * Implementation of a {@link HeaderIterator} based on a {@link List}.
40 * For use by {@link HeaderGroup}.
41 *
42 * @since 4.0
43 */
44 public class BasicListHeaderIterator implements HeaderIterator {
45
46 /**
47 * A list of headers to iterate over.
48 * Not all elements of this array are necessarily part of the iteration.
49 */
50 protected final List<Header> allHeaders;
51
52
53 /**
54 * The position of the next header in {@link #allHeaders allHeaders}.
55 * Negative if the iteration is over.
56 */
57 protected int currentIndex;
58
59
60 /**
61 * The position of the last returned header.
62 * Negative if none has been returned so far.
63 */
64 protected int lastIndex;
65
66
67 /**
68 * The header name to filter by.
69 * {@code null} to iterate over all headers in the array.
70 */
71 protected String headerName;
72
73
74
75 /**
76 * Creates a new header iterator.
77 *
78 * @param headers a list of headers over which to iterate
79 * @param name the name of the headers over which to iterate, or
80 * {@code null} for any
81 */
82 public BasicListHeaderIterator(final List<Header> headers, final String name) {
83 super();
84 this.allHeaders = Args.notNull(headers, "Header list");
85 this.headerName = name;
86 this.currentIndex = findNext(-1);
87 this.lastIndex = -1;
88 }
89
90
91 /**
92 * Determines the index of the next header.
93 *
94 * @param pos one less than the index to consider first,
95 * -1 to search for the first header
96 *
97 * @return the index of the next header that matches the filter name,
98 * or negative if there are no more headers
99 */
100 protected int findNext(final int pos) {
101 int from = pos;
102 if (from < -1) {
103 return -1;
104 }
105
106 final int to = this.allHeaders.size()-1;
107 boolean found = false;
108 while (!found && (from < to)) {
109 from++;
110 found = filterHeader(from);
111 }
112 return found ? from : -1;
113 }
114
115
116 /**
117 * Checks whether a header is part of the iteration.
118 *
119 * @param index the index of the header to check
120 *
121 * @return {@code true} if the header should be part of the
122 * iteration, {@code false} to skip
123 */
124 protected boolean filterHeader(final int index) {
125 if (this.headerName == null) {
126 return true;
127 }
128
129 // non-header elements, including null, will trigger exceptions
130 final String name = (this.allHeaders.get(index)).getName();
131
132 return this.headerName.equalsIgnoreCase(name);
133 }
134
135
136 // non-javadoc, see interface HeaderIterator
137 @Override
138 public boolean hasNext() {
139 return (this.currentIndex >= 0);
140 }
141
142
143 /**
144 * Obtains the next header from this iteration.
145 *
146 * @return the next header in this iteration
147 *
148 * @throws NoSuchElementException if there are no more headers
149 */
150 @Override
151 public Header nextHeader()
152 throws NoSuchElementException {
153
154 final int current = this.currentIndex;
155 if (current < 0) {
156 throw new NoSuchElementException("Iteration already finished.");
157 }
158
159 this.lastIndex = current;
160 this.currentIndex = findNext(current);
161
162 return this.allHeaders.get(current);
163 }
164
165
166 /**
167 * Returns the next header.
168 * Same as {@link #nextHeader nextHeader}, but not type-safe.
169 *
170 * @return the next header in this iteration
171 *
172 * @throws NoSuchElementException if there are no more headers
173 */
174 @Override
175 public final Object next()
176 throws NoSuchElementException {
177 return nextHeader();
178 }
179
180
181 /**
182 * Removes the header that was returned last.
183 */
184 @Override
185 public void remove()
186 throws UnsupportedOperationException {
187 Asserts.check(this.lastIndex >= 0, "No header to remove");
188 this.allHeaders.remove(this.lastIndex);
189 this.lastIndex = -1;
190 this.currentIndex--; // adjust for the removed element
191 }
192 }