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    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.io;
039     
040    import 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     */
058    public 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    }