Source for java.io.Reader

   1: /* Reader.java -- base class of classes that read input as a stream of chars
   2:    Copyright (C) 1998, 1999, 2000, 2003, 2004, 2005  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: import java.nio.CharBuffer;
  41: 
  42: /* Written using "Java Class Libraries", 2nd edition, plus online
  43:  * API docs for JDK 1.2 beta from http://www.javasoft.com.
  44:  * Status:  Believed complete and correct.
  45:  */
  46: 
  47: /**
  48:  * This abstract class forms the base of the hierarchy of classes that read
  49:  * input as a stream of characters.  It provides a common set of methods for
  50:  * reading characters from streams.  Subclasses implement and extend these
  51:  * methods to read characters from a particular input source such as a file
  52:  * or network connection.
  53:  *
  54:  * @author Per Bothner (bothner@cygnus.com)
  55:  * @date April 21, 1998.
  56:  * @author Aaron M. Renn (arenn@urbanophile.com)
  57:  */
  58: public abstract class Reader implements Closeable, Readable
  59: {
  60:   /**
  61:    * This is the <code>Object</code> used for synchronizing critical code
  62:    * sections.  Subclasses should use this variable instead of a
  63:    * synchronized method or an explicit synchronization on <code>this</code>
  64:    */
  65:   protected Object lock;
  66: 
  67:   /**
  68:     * Unitializes a <code>Reader</code> that will use the object
  69:     * itself for synchronization of critical code sections.
  70:     */
  71:   protected Reader()
  72:   {
  73:     this.lock = this;
  74:   }
  75: 
  76:   /**
  77:     * Initializes a <code>Reader</code> that will use the specified
  78:     * <code>Object</code> for synchronization of critical code sections.
  79:     *
  80:     * @param lock The <code>Object</code> to use for synchronization
  81:     */
  82:   protected Reader(Object lock)
  83:   {
  84:     this.lock = lock;
  85:   }
  86: 
  87:   /**
  88:    * Read chars from a stream and stores them into a caller
  89:    * supplied buffer.  It starts storing the data at index <code>offset</code>
  90:    * into the buffer and attempts to read <code>len</code> chars.  This method
  91:    * can return before reading the number of chars requested.  The actual
  92:    * number of chars read is returned as an int.  A -1 is returned to indicate
  93:    * the end of the stream.
  94:    * <p>
  95:    * This method will block until some data can be read.
  96:    * <p>
  97:    * This method operates by calling the single char <code>read()</code> method
  98:    * in a loop until the desired number of chars are read.  The read loop
  99:    * 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: }