001    /* CharArrayReader.java -- Read an array of characters as a stream
002       Copyright (C) 1998, 2001, 2005  Free Software Foundation, Inc.
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    
039    package java.io;
040    
041    /**
042      * This class permits an array of chars to be read as an input stream.
043      *
044      * @author Aaron M. Renn (arenn@urbanophile.com)
045      * @author Warren Levy (warrenl@cygnus.com)
046      */
047    public class CharArrayReader extends Reader
048    {
049      /**
050       * The array that contains the data supplied during read operations
051       */
052      protected char[] buf;
053    
054      /**
055       * The array index of the next char to be read from the buffer
056       * <code>buf</code>
057       */
058      protected int pos;
059    
060      /**
061       * The currently marked position in the stream.  This defaults to 0, so a
062       * reset operation on the stream resets it to read from array index 0 in
063       * the buffer - even if the stream was initially created with an offset
064       * greater than 0
065       */
066      protected int markedPos;
067    
068      /**
069       * This indicates the maximum number of chars that can be read from this
070       * stream.  It is the array index of the position after the last valid
071       * char in the buffer <code>buf</code>
072       */
073      protected int count;
074    
075      /**
076       * Create a new CharArrayReader that will read chars from the passed
077       * in char array.  This stream will read from the beginning to the end
078       * of the array.  It is identical to calling an overloaded constructor
079       * as <code>CharArrayReader(buf, 0, buf.length)</code>.
080       * <p>
081       * Note that this array is not copied.  If its contents are changed
082       * while this stream is being read, those changes will be reflected in the
083       * chars supplied to the reader.  Please use caution in changing the
084       * contents of the buffer while this stream is open.
085       *
086       * @param buffer The char array buffer this stream will read from.
087      */
088      public CharArrayReader(char[] buffer)
089      {
090        this(buffer, 0, buffer.length);
091      }
092    
093      /**
094       * Create a new CharArrayReader that will read chars from the passed
095       * in char array.  This stream will read from position
096       * <code>offset</code> in the array for a length of
097       * <code>length</code> chars past <code>offset</code>.  If the
098       * stream is reset to a position before <code>offset</code> then
099       * more than <code>length</code> chars can be read from the stream.
100       * The <code>length</code> value should be viewed as the array index
101       * one greater than the last position in the buffer to read.
102       * <p>
103       * Note that this array is not copied.  If its contents are changed
104       * while this stream is being read, those changes will be reflected in the
105       * chars supplied to the reader.  Please use caution in changing the
106       * contents of the buffer while this stream is open.
107       *
108       * @param buffer The char array buffer this stream will read from.
109       * @param offset The index into the buffer to start reading chars from
110       * @param length The number of chars to read from the buffer
111       */
112      public CharArrayReader(char[] buffer, int offset, int length)
113      {
114        super();
115        if (offset < 0  || length < 0 || offset > buffer.length)
116          throw new IllegalArgumentException();
117    
118        buf = buffer;
119    
120        count = offset + length;
121        if (count > buf.length)
122          count = buf.length;
123    
124        pos = offset;
125        markedPos = pos;
126      }
127    
128      /**
129       * This method closes the stream.
130       */
131      public void close()
132      {
133        synchronized (lock)
134          {
135            buf = null;
136          }
137      }
138    
139      /**
140       * This method sets the mark position in this stream to the current
141       * position.  Note that the <code>readlimit</code> parameter in this
142       * method does nothing as this stream is always capable of
143       * remembering all the chars int it.
144       * <p>
145       * Note that in this class the mark position is set by default to
146       * position 0 in the stream.  This is in constrast to some other
147       * stream types where there is no default mark position.
148       *
149       * @param readAheadLimit The number of chars this stream must
150       *                       remember.  This parameter is ignored.
151       *
152       * @exception IOException If an error occurs
153       */
154      public void mark(int readAheadLimit) throws IOException
155      {
156        synchronized (lock)
157          {
158            if (buf == null)
159              throw new IOException("Stream closed");
160            // readAheadLimit is ignored per Java Class Lib. book, p. 318.
161            markedPos = pos;
162          }
163      }
164    
165      /**
166       * This method overrides the <code>markSupported</code> method in
167       * <code>Reader</code> in order to return <code>true</code> -
168       * indicating that this stream class supports mark/reset
169       * functionality.
170       *
171       * @return <code>true</code> to indicate that this class supports
172       * mark/reset.
173       */
174      public boolean markSupported()
175      {
176        return true;
177      }
178    
179      /**
180       * This method reads one char from the stream.  The <code>pos</code>
181       * counter is advanced to the next char to be read.  The char read
182       * is returned as an int in the range of 0-65535.  If the stream
183       * position is already at the end of the buffer, no char is read and
184       * a -1 is returned in order to indicate the end of the stream.
185       *
186       * @return The char read, or -1 if end of stream
187       */
188      public int read() throws IOException
189      {
190        synchronized (lock)
191          {
192            if (buf == null)
193              throw new IOException("Stream closed");
194    
195            if (pos < 0)
196              throw new ArrayIndexOutOfBoundsException(pos);
197    
198            if (pos < count)
199              return ((int) buf[pos++]) & 0xFFFF;
200            return -1;
201          }
202      }
203    
204      /**
205       * This method reads chars from the stream and stores them into a
206       * caller supplied buffer.  It starts storing the data at index
207       * <code>offset</code> into the buffer and attempts to read
208       * <code>len</code> chars.  This method can return before reading
209       * the number of chars requested if the end of the stream is
210       * encountered first.  The actual number of chars read is returned.
211       * If no chars can be read because the stream is already at the end
212       * of stream position, a -1 is returned.
213       * <p>
214       * This method does not block.
215       *
216       * @param b The array into which the chars read should be stored.
217       * @param off The offset into the array to start storing chars
218       * @param len The requested number of chars to read
219       *
220       * @return The actual number of chars read, or -1 if end of stream.
221       */
222      public int read(char[] b, int off, int len) throws IOException
223      {
224        synchronized (lock)
225          {
226            if (buf == null)
227              throw new IOException("Stream closed");
228    
229            /* Don't need to check pos value, arraycopy will check it. */
230            if (off < 0 || len < 0 || off + len > b.length)
231              throw new IndexOutOfBoundsException();
232    
233            if (pos >= count)
234              return -1;
235    
236            int numChars = Math.min(count - pos, len);
237            System.arraycopy(buf, pos, b, off, numChars);
238            pos += numChars;
239            return numChars;
240          }
241      }
242    
243      /**
244       * Return true if more characters are available to be read.
245       *
246       * @return <code>true</code> to indicate that this stream is ready
247       * to be read.
248       *
249       * @specnote The JDK 1.3 API docs are wrong here. This method will
250       *           return false if there are no more characters available.
251       */
252      public boolean ready() throws IOException
253      {
254        if (buf == null)
255          throw new IOException("Stream closed");
256    
257        return (pos < count);
258      }
259    
260      /**
261       * This method sets the read position in the stream to the mark
262       * point by setting the <code>pos</code> variable equal to the
263       * <code>mark</code> variable.  Since a mark can be set anywhere in
264       * the array, the mark/reset methods int this class can be used to
265       * provide random search capabilities for this type of stream.
266       */
267      public void reset() throws IOException
268      {
269        synchronized (lock)
270          {
271            if (buf == null)
272              throw new IOException("Stream closed");
273    
274            pos = markedPos;
275          }
276      }
277    
278      /**
279       * This method attempts to skip the requested number of chars in the
280       * input stream.  It does this by advancing the <code>pos</code> value by the
281       * specified number of chars.  It this would exceed the length of the
282       * buffer, then only enough chars are skipped to position the stream at
283       * the end of the buffer.  The actual number of chars skipped is returned.
284       *
285       * @param n The requested number of chars to skip
286       *
287       * @return The actual number of chars skipped.
288       */
289      public long skip(long n) throws IOException
290      {
291        synchronized (lock)
292          {
293            if (buf == null)
294              throw new IOException("Stream closed");
295    
296            // Even though the var numChars is a long, in reality it can never
297            // be larger than an int since the result of subtracting 2 positive
298            // ints will always fit in an int.  Since we have to return a long
299            // anyway, numChars might as well just be a long.
300            long numChars = Math.min((long) (count - pos), n < 0 ? 0L : n);
301            pos += numChars;
302            return numChars;
303          }
304      }
305    }