001/* Reader.java -- base class of classes that read input as a stream of chars
002   Copyright (C) 1998, 1999, 2000, 2003, 2004, 2005  Free Software Foundation
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010 
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038package java.io;
039 
040import java.nio.CharBuffer;
041
042/* Written using "Java Class Libraries", 2nd edition, plus online
043 * API docs for JDK 1.2 beta from http://www.javasoft.com.
044 * Status:  Believed complete and correct.
045 */
046
047/**
048 * This abstract class forms the base of the hierarchy of classes that read
049 * input as a stream of characters.  It provides a common set of methods for
050 * reading characters from streams.  Subclasses implement and extend these
051 * methods to read characters from a particular input source such as a file
052 * or network connection.
053 *
054 * @author Per Bothner (bothner@cygnus.com)
055 * @date April 21, 1998.  
056 * @author Aaron M. Renn (arenn@urbanophile.com) 
057 */
058public abstract class Reader implements Closeable, Readable
059{
060  /**
061   * This is the <code>Object</code> used for synchronizing critical code
062   * sections.  Subclasses should use this variable instead of a 
063   * synchronized method or an explicit synchronization on <code>this</code>
064   */
065  protected Object lock;
066  
067  /**
068    * Unitializes a <code>Reader</code> that will use the object
069    * itself for synchronization of critical code sections.
070    */
071  protected Reader()
072  {
073    this.lock = this;
074  }
075
076  /**
077    * Initializes a <code>Reader</code> that will use the specified
078    * <code>Object</code> for synchronization of critical code sections.
079    *
080    * @param lock The <code>Object</code> to use for synchronization
081    */
082  protected Reader(Object lock)
083  {
084    this.lock = lock;
085  }
086
087  /**
088   * Read chars from a stream and stores them into a caller
089   * supplied buffer.  It starts storing the data at index <code>offset</code> 
090   * into the buffer and attempts to read <code>len</code> chars.  This method 
091   * can return before reading the number of chars requested.  The actual 
092   * number of chars read is returned as an int.  A -1 is returned to indicate 
093   * the end of the stream.
094   * <p>
095   * This method will block until some data can be read.
096   * <p>
097   * This method operates by calling the single char <code>read()</code> method
098   * in a loop until the desired number of chars are read.  The read loop
099   * stops short if the end of the stream is encountered or if an IOException
100   * is encountered on any read operation except the first.  If the first
101   * attempt to read a chars fails, the IOException is allowed to propagate
102   * upward.  And subsequent IOException is caught and treated identically
103   * to an end of stream condition.  Subclasses can (and should if possible)
104   * override this method to provide a more efficient implementation.
105   *
106   * @param buf The array into which the chars read should be stored
107   * @param offset The offset into the array to start storing chars
108   * @param count The requested number of chars to read
109   *
110   * @return The actual number of chars read, or -1 if end of stream.
111   *
112   * @exception IOException If an error occurs.
113   */
114  public abstract int read(char buf[], int offset, int count)
115    throws IOException;
116    
117  /**
118   * Reads chars from a stream and stores them into a caller
119   * supplied buffer.  This method attempts to completely fill the buffer,
120   * but can return before doing so.  The actual number of chars read is
121   * returned as an int.  A -1 is returned to indicate the end of the stream.
122   * <p>
123   * This method will block until some data can be read.
124   * <p>
125   * This method operates by calling an overloaded read method like so:
126   * <code>read(buf, 0, buf.length)</code>
127   *
128   * @param buf The buffer into which the chars read will be stored.
129   *
130   * @return The number of chars read or -1 if end of stream.
131   *
132   * @exception IOException If an error occurs.
133   */
134  public int read(char buf[]) throws IOException
135  {
136    return read(buf, 0, buf.length);
137  }
138
139  /**
140   * Reads an char from the input stream and returns it
141   * as an int in the range of 0-65535.  This method also will return -1 if
142   * the end of the stream has been reached.
143   * <p>
144   * This method will block until the char can be read.
145   *
146   * @return The char read or -1 if end of stream
147   *
148   * @exception IOException If an error occurs
149   */
150  public int read() throws IOException
151  {
152    char[] buf = new char[1];
153    int count = read(buf, 0, 1);
154    return count > 0 ? buf[0] : -1;
155  }
156
157  /** @since 1.5 */
158  public int read(CharBuffer buffer) throws IOException
159  {
160    // We want to call put(), so we don't manipulate the CharBuffer
161    // directly.
162    int rem = buffer.remaining();
163    char[] buf = new char[rem];
164    int result = read(buf, 0, rem);
165    if (result != -1)
166      buffer.put(buf, 0, result);
167    return result;
168  }
169
170  /**
171   * Closes the stream.  Any futher attempts to read from the
172   * stream may generate an <code>IOException</code>.
173   *
174   * @exception IOException If an error occurs
175   */
176  public abstract void close() throws IOException;
177
178  /**
179   * Returns a boolean that indicates whether the mark/reset
180   * methods are supported in this class.  Those methods can be used to
181   * remember a specific point in the stream and reset the stream to that
182   * point.
183   * <p>
184   * This method always returns <code>false</code> in this class, but
185   * subclasses can override this method to return <code>true</code> if they 
186   * support mark/reset functionality.
187   *
188   * @return <code>true</code> if mark/reset functionality is supported, 
189   *         <code>false</code> otherwise
190   *
191   */
192  public boolean markSupported()
193  {
194    return false;
195  }
196
197  /**
198    * Marks a position in the input to which the stream can be
199    * "reset" by calling the <code>reset()</code> method.  The parameter
200    * <code>readlimit</code> is the number of chars that can be read from the 
201    * stream after setting the mark before the mark becomes invalid.  For
202    * example, if <code>mark()</code> is called with a read limit of 10, then 
203    * when 11 chars of data are read from the stream before the 
204    * <code>reset()</code> method is called, then the mark is invalid and the 
205    * stream object instance is not required to remember the mark.
206    *
207    * @param readLimit The number of chars that can be read before the mark 
208    *        becomes invalid
209    *
210    * @exception IOException If an error occurs such as mark not being 
211    *            supported for this class
212    */
213  public void mark(int readLimit) throws IOException
214  {
215    throw new IOException("mark not supported");
216  }
217
218  /**
219    * Resets a stream to the point where the <code>mark()</code> 
220    * method was called.  Any chars that were read after the mark point was 
221    * set will be re-read during subsequent reads.
222    * <p>
223    * This method always throws an IOException in this class, but subclasses
224    * can override this method if they provide mark/reset functionality.
225    *
226    * @exception IOException Always thrown for this class
227    */
228  public void reset() throws IOException
229  {
230    throw new IOException("reset not supported");
231  }
232
233  /**
234    * Determines whether or not this stream is ready to be
235    * read.  If it returns <code>false</code> the stream may block if a
236    * read is attempted, but it is not guaranteed to do so.
237    * <p>
238    * This method always returns <code>false</code> in this class
239    *
240    * @return <code>true</code> if the stream is ready to be read, 
241    * <code>false</code> otherwise.
242    *
243    * @exception IOException If an error occurs
244    */
245  public boolean ready() throws IOException
246  {
247    return false;
248  }
249
250  /**
251    * Skips the specified number of chars in the stream.  It
252    * returns the actual number of chars skipped, which may be less than the
253    * requested amount.
254    * <p>
255    * This method reads and discards chars into a 256 char array until the
256    * specified number of chars were skipped or until either the end of stream
257    * is reached or a read attempt returns a short count.  Subclasses can
258    * override this method to provide a more efficient implementation where
259    * one exists.
260    *
261    * @param count The requested number of chars to skip
262    *
263    * @return The actual number of chars skipped.
264    *
265    * @exception IOException If an error occurs
266    */
267  public long skip(long count) throws IOException
268  {
269    if (count <= 0)
270      return 0;
271    int bsize = count > 1024 ? 1024 : (int) count;
272    char[] buffer = new char[bsize];
273    long todo = count;
274    synchronized (lock)
275    {
276      while (todo > 0)
277        {
278          int skipped = read(buffer, 0, bsize > todo ? (int) todo : bsize);
279          if (skipped <= 0)
280            break;
281          todo -= skipped;
282        }
283    }
284    return count - todo;
285  }
286}