Source for java.io.StringReader

   1: /* StringReader.java -- permits a String to be read as a character input stream
   2:    Copyright (C) 1998, 1999, 2000, 2003  Free Software Foundation
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10:  
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package java.io;
  39: 
  40: /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  41:  * "The Java Language Specification", ISBN 0-201-63451-1
  42:  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  43:  * Status:  Believed complete and correct
  44:  */
  45: 
  46: /**
  47:  * This class permits a <code>String</code> to be read as a character 
  48:  * input stream.
  49:  * <p>
  50:  * The mark/reset functionality in this class behaves differently than
  51:  * normal.  If no mark has been set, then calling the <code>reset()</code>
  52:  * method rewinds the read pointer to the beginning of the <code>String</code>.
  53:  *
  54:  * @author Aaron M. Renn (arenn@urbanophile.com)
  55:  * @author Warren Levy (warrenl@cygnus.com)
  56:  * @date October 19, 1998.  
  57:  */
  58: public class StringReader extends Reader
  59: {
  60:   /* A String provided by the creator of the stream. */
  61:   private String buf;
  62: 
  63:   /* Position of the next char in buf to be read. */
  64:   private int pos;
  65: 
  66:   /* The currently marked position in the stream. */
  67:   private int markedPos;
  68: 
  69:   /* The index in buf one greater than the last valid character. */
  70:   private int count;
  71: 
  72:   /**
  73:    * Create a new <code>StringReader</code> that will read chars from the 
  74:    * passed in <code>String</code>.  This stream will read from the beginning 
  75:    * to the end of the <code>String</code>.
  76:    *
  77:    * @param buffer The <code>String</code> this stream will read from.
  78:    */
  79:   public StringReader(String buffer)
  80:   {
  81:     super();
  82:     buf = buffer;
  83: 
  84:     count = buffer.length();
  85:     markedPos = pos = 0;
  86:   }
  87: 
  88:   public void close()
  89:   {
  90:     synchronized (lock)
  91:     {
  92:       buf = null;
  93:     }
  94:   }
  95: 
  96:   public void mark(int readAheadLimit) throws IOException
  97:   {
  98:     synchronized (lock)
  99:     {
 100:       if (buf == null)
 101:         throw new IOException("Stream closed");
 102: 
 103:       // readAheadLimit is ignored per Java Class Lib. book, p. 1692.
 104:       markedPos = pos;
 105:     }
 106:   }
 107: 
 108:   public boolean markSupported()
 109:   {
 110:     return true;
 111:   }
 112: 
 113:   public int read() throws IOException
 114:   {
 115:     synchronized (lock)
 116:     {
 117:       if (buf == null)
 118:         throw new IOException("Stream closed");
 119: 
 120:       if (pos < count)
 121:         return ((int) buf.charAt(pos++)) & 0xFFFF;
 122:       return -1;
 123:     }
 124:   }
 125: 
 126:   public int read(char[] b, int off, int len) throws IOException
 127:   {
 128:     synchronized (lock)
 129:     {
 130:       if (buf == null)
 131:         throw new IOException("Stream closed");
 132: 
 133:       /* Don't need to check pos value, arraycopy will check it. */
 134:       if (off < 0 || len < 0 || off + len > b.length)
 135:         throw new ArrayIndexOutOfBoundsException();
 136: 
 137:       if (pos >= count)
 138:         return -1;
 139: 
 140:       int lastChar = Math.min(count, pos + len);
 141:       buf.getChars(pos, lastChar, b, off);
 142:       int numChars = lastChar - pos;
 143:       pos = lastChar;
 144:       return numChars;
 145:     }
 146:   }
 147: 
 148:   /**
 149:    * This method determines if the stream is ready to be read.  This class
 150:    * is always ready to read and so always returns <code>true</code>, unless
 151:    * close() has previously been called in which case an IOException is
 152:    * thrown.
 153:    *
 154:    * @return <code>true</code> to indicate that this object is ready to be read.
 155:    * @exception IOException If the stream is closed.
 156:    */
 157:   public boolean ready() throws IOException
 158:   {
 159:     if (buf == null)
 160:       throw new IOException("Stream closed");
 161: 
 162:     return true;
 163:   }
 164: 
 165:   /**
 166:    * Sets the read position in the stream to the previously
 167:    * marked position or to 0 (i.e., the beginning of the stream) if the mark
 168:    * has not already been set.
 169:    */
 170:   public void reset() throws IOException
 171:   {
 172:     synchronized (lock)
 173:     {
 174:       if (buf == null)
 175:         throw new IOException("Stream closed");
 176: 
 177:       pos = markedPos;
 178:     }
 179:   }
 180: 
 181:   /**
 182:     * This method attempts to skip the requested number of chars in the
 183:     * input stream.  It does this by advancing the <code>pos</code> value by 
 184:     * the specified number of chars.  It this would exceed the length of the
 185:     * buffer, then only enough chars are skipped to position the stream at
 186:     * the end of the buffer.  The actual number of chars skipped is returned.
 187:     *
 188:     * @param n The requested number of chars to skip
 189:     *
 190:     * @return The actual number of chars skipped.
 191:     */
 192:   public long skip(long n) throws IOException
 193:   {
 194:     synchronized (lock)
 195:     {
 196:       if (buf == null)
 197:         throw new IOException("Stream closed");
 198: 
 199:       // Even though the var numChars is a long, in reality it can never
 200:       // be larger than an int since the result of subtracting 2 positive
 201:       // ints will always fit in an int.  Since we have to return a long
 202:       // anyway, numChars might as well just be a long.
 203:       long numChars = Math.min((long) (count - pos), n < 0 ? 0L : n);
 204:       pos += numChars;
 205:       return numChars;
 206:     }
 207:   }
 208: }