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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.io.input;
18  
19  import java.io.EOFException;
20  import java.io.IOException;
21  import java.io.Reader;
22  
23  /**
24   * A functional, light weight {@link Reader} that emulates
25   * a reader of a specified size.
26   * <p>
27   * This implementation provides a light weight
28   * object for testing with an {@link Reader}
29   * where the contents don't matter.
30   * <p>
31   * One use case would be for testing the handling of
32   * large {@link Reader} as it can emulate that
33   * scenario without the overhead of actually processing
34   * large numbers of characters - significantly speeding up
35   * test execution times.
36   * <p>
37   * This implementation returns a space from the method that
38   * reads a character and leaves the array unchanged in the read
39   * methods that are passed a character array.
40   * If alternative data is required the <code>processChar()</code> and
41   * <code>processChars()</code> methods can be implemented to generate
42   * data, for example:
43   *
44   * <pre>
45   *  public class TestReader extends NullReader {
46   *      public TestReader(int size) {
47   *          super(size);
48   *      }
49   *      protected char processChar() {
50   *          return ... // return required value here
51   *      }
52   *      protected void processChars(char[] chars, int offset, int length) {
53   *          for (int i = offset; i < length; i++) {
54   *              chars[i] = ... // set array value here
55   *          }
56   *      }
57   *  }
58   * </pre>
59   *
60   * @since Commons IO 1.3
61   * @version $Revision: 463529 $
62   */
63  public class NullReader extends Reader {
64  
65      private long size;
66      private long position;
67      private long mark = -1;
68      private long readlimit;
69      private boolean eof;
70      private boolean throwEofException;
71      private boolean markSupported;
72  
73      /**
74       * Create a {@link Reader} that emulates a specified size
75       * which supports marking and does not throw EOFException.
76       *
77       * @param size The size of the reader to emulate.
78       */
79      public NullReader(long size) {
80         this(size, true, false);
81      }
82  
83      /**
84       * Create a {@link Reader} that emulates a specified
85       * size with option settings.
86       *
87       * @param size The size of the reader to emulate.
88       * @param markSupported Whether this instance will support
89       * the <code>mark()</code> functionality.
90       * @param throwEofException Whether this implementation
91       * will throw an {@link EOFException} or return -1 when the
92       * end of file is reached.
93       */
94      public NullReader(long size, boolean markSupported, boolean throwEofException) {
95         this.size = size;
96         this.markSupported = markSupported;
97         this.throwEofException = throwEofException;
98      }
99  
100     /**
101      * Return the current position.
102      *
103      * @return the current position.
104      */
105     public long getPosition() {
106         return position;
107     }
108 
109     /**
110      * Return the size this {@link Reader} emulates.
111      *
112      * @return The size of the reader to emulate.
113      */
114     public long getSize() {
115         return size;
116     }
117 
118     /**
119      * Close this Reader - resets the internal state to
120      * the initial values.
121      *
122      * @throws IOException If an error occurs.
123      */
124     public void close() throws IOException {
125         eof = false;
126         position = 0;
127         mark = -1;
128     }
129 
130     /**
131      * Mark the current position.
132      *
133      * @param readlimit The number of characters before this marked position
134      * is invalid.
135      * @throws UnsupportedOperationException if mark is not supported.
136      */
137     public synchronized void mark(int readlimit) {
138         if (!markSupported) {
139             throw new UnsupportedOperationException("Mark not supported");
140         }
141         mark = position;
142         this.readlimit = readlimit;
143     }
144 
145     /**
146      * Indicates whether <i>mark</i> is supported.
147      *
148      * @return Whether <i>mark</i> is supported or not.
149      */
150     public boolean markSupported() {
151         return markSupported;
152     }
153 
154     /**
155      * Read a character.
156      *
157      * @return Either The character value returned by <code>processChar()</code>
158      * or <code>-1</code> if the end of file has been reached and
159      * <code>throwEofException</code> is set to <code>false</code>.
160      * @throws EOFException if the end of file is reached and
161      * <code>throwEofException</code> is set to <code>true</code>.
162      * @throws IOException if trying to read past the end of file.
163      */
164     public int read() throws IOException {
165         if (eof) {
166             throw new IOException("Read after end of file");
167         }
168         if (position == size) {
169             return doEndOfFile();
170         }
171         position++;
172         return processChar();
173     }
174 
175     /**
176      * Read some characters into the specified array.
177      *
178      * @param chars The character array to read into
179      * @return The number of characters read or <code>-1</code>
180      * if the end of file has been reached and
181      * <code>throwEofException</code> is set to <code>false</code>.
182      * @throws EOFException if the end of file is reached and
183      * <code>throwEofException</code> is set to <code>true</code>.
184      * @throws IOException if trying to read past the end of file.
185      */
186     public int read(char[] chars) throws IOException {
187         return read(chars, 0, chars.length);
188     }
189 
190     /**
191      * Read the specified number characters into an array.
192      *
193      * @param chars The character array to read into.
194      * @param offset The offset to start reading characters into.
195      * @param length The number of characters to read.
196      * @return The number of characters read or <code>-1</code>
197      * if the end of file has been reached and
198      * <code>throwEofException</code> is set to <code>false</code>.
199      * @throws EOFException if the end of file is reached and
200      * <code>throwEofException</code> is set to <code>true</code>.
201      * @throws IOException if trying to read past the end of file.
202      */
203     public int read(char[] chars, int offset, int length) throws IOException {
204         if (eof) {
205             throw new IOException("Read after end of file");
206         }
207         if (position == size) {
208             return doEndOfFile();
209         }
210         position += length;
211         int returnLength = length;
212         if (position > size) {
213             returnLength = length - (int)(position - size);
214             position = size;
215         }
216         processChars(chars, offset, returnLength);
217         return returnLength;
218     }
219 
220     /**
221      * Reset the stream to the point when mark was last called.
222      *
223      * @throws UnsupportedOperationException if mark is not supported.
224      * @throws IOException If no position has been marked
225      * or the read limit has been exceed since the last position was
226      * marked.
227      */
228     public synchronized void reset() throws IOException {
229         if (!markSupported) {
230             throw new UnsupportedOperationException("Mark not supported");
231         }
232         if (mark < 0) {
233             throw new IOException("No position has been marked");
234         }
235         if (position > (mark + readlimit)) {
236             throw new IOException("Marked position [" + mark +
237                     "] is no longer valid - passed the read limit [" +
238                     readlimit + "]");
239         }
240         position = mark;
241         eof = false;
242     }
243 
244     /**
245      * Skip a specified number of characters.
246      *
247      * @param numberOfChars The number of characters to skip.
248      * @return The number of characters skipped or <code>-1</code>
249      * if the end of file has been reached and
250      * <code>throwEofException</code> is set to <code>false</code>.
251      * @throws EOFException if the end of file is reached and
252      * <code>throwEofException</code> is set to <code>true</code>.
253      * @throws IOException if trying to read past the end of file.
254      */
255     public long skip(long numberOfChars) throws IOException {
256         if (eof) {
257             throw new IOException("Skip after end of file");
258         }
259         if (position == size) {
260             return doEndOfFile();
261         }
262         position += numberOfChars;
263         long returnLength = numberOfChars;
264         if (position > size) {
265             returnLength = numberOfChars - (position - size);
266             position = size;
267         }
268         return returnLength;
269     }
270 
271     /**
272      * Return a character value for the  <code>read()</code> method.
273      * <p>
274      * This implementation returns zero.
275      *
276      * @return This implementation always returns zero.
277      */
278     protected int processChar() {
279         // do nothing - overridable by subclass
280         return 0;
281     }
282 
283     /**
284      * Process the characters for the <code>read(char[], offset, length)</code>
285      * method.
286      * <p>
287      * This implementation leaves the character array unchanged.
288      *
289      * @param chars The character array
290      * @param offset The offset to start at.
291      * @param length The number of characters.
292      */
293     protected void processChars(char[] chars, int offset, int length) {
294         // do nothing - overridable by subclass
295     }
296 
297     /**
298      * Handle End of File.
299      *
300      * @return <code>-1</code> if <code>throwEofException</code> is
301      * set to <code>false</code>
302      * @throws EOFException if <code>throwEofException</code> is set
303      * to <code>true</code>.
304      */
305     private int doEndOfFile() throws EOFException {
306         eof = true;
307         if (throwEofException) {
308             throw new EOFException();
309         }
310         return -1;
311     }
312 
313 }