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  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, plus online
  41:  * API docs for JDK 1.2 beta from http://www.javasoft.com.
  42:  * Status:  Believed complete and correct.
  43:  */
  44: 
  45: /**
  46:  * This abstract class forms the base of the hierarchy of classes that read
  47:  * input as a stream of characters.  It provides a common set of methods for
  48:  * reading characters from streams.  Subclasses implement and extend these
  49:  * methods to read characters from a particular input source such as a file
  50:  * or network connection.
  51:  *
  52:  * @author Per Bothner (bothner@cygnus.com)
  53:  * @date April 21, 1998.  
  54:  * @author Aaron M. Renn (arenn@urbanophile.com) 
  55:  */
  56: public abstract class Reader
  57: {
  58:   /**
  59:    * This is the <code>Object</code> used for synchronizing critical code
  60:    * sections.  Subclasses should use this variable instead of a 
  61:    * synchronized method or an explicit synchronization on <code>this</code>
  62:    */
  63:   protected Object lock;
  64:   
  65:   /**
  66:     * Unitializes a <code>Reader</code> that will use the object
  67:     * itself for synchronization of critical code sections.
  68:     */
  69:   protected Reader()
  70:   {
  71:     this.lock = this;
  72:   }
  73: 
  74:   /**
  75:     * Initializes a <code>Reader</code> that will use the specified
  76:     * <code>Object</code> for synchronization of critical code sections.
  77:     *
  78:     * @param lock The <code>Object</code> to use for synchronization
  79:     */
  80:   protected Reader(Object lock)
  81:   {
  82:     this.lock = lock;
  83:   }
  84: 
  85:   /**
  86:    * Read chars from a stream and stores them into a caller
  87:    * supplied buffer.  It starts storing the data at index <code>offset</code> 
  88:    * into the buffer and attempts to read <code>len</code> chars.  This method 
  89:    * can return before reading the number of chars requested.  The actual 
  90:    * number of chars read is returned as an int.  A -1 is returned to indicate 
  91:    * the end of the stream.
  92:    * <p>
  93:    * This method will block until some data can be read.
  94:    * <p>
  95:    * This method operates by calling the single char <code>read()</code> method
  96:    * in a loop until the desired number of chars are read.  The read loop
  97:    * stops short if the end of the stream is encountered or if an IOException
  98:    * is encountered on any read operation except the first.  If the first
  99:    * attempt to read a chars fails, the IOException is allowed to propagate
 100:    * upward.  And subsequent IOException is caught and treated identically
 101:    * to an end of stream condition.  Subclasses can (and should if possible)
 102:    * override this method to provide a more efficient implementation.
 103:    *
 104:    * @param buf The array into which the chars read should be stored
 105:    * @param offset The offset into the array to start storing chars
 106:    * @param count The requested number of chars to read
 107:    *
 108:    * @return The actual number of chars read, or -1 if end of stream.
 109:    *
 110:    * @exception IOException If an error occurs.
 111:    */
 112:   public abstract int read(char buf[], int offset, int count)
 113:     throws IOException;
 114:     
 115:   /**
 116:    * Reads chars from a stream and stores them into a caller
 117:    * supplied buffer.  This method attempts to completely fill the buffer,
 118:    * but can return before doing so.  The actual number of chars read is
 119:    * returned as an int.  A -1 is returned to indicate the end of the stream.
 120:    * <p>
 121:    * This method will block until some data can be read.
 122:    * <p>
 123:    * This method operates by calling an overloaded read method like so:
 124:    * <code>read(buf, 0, buf.length)</code>
 125:    *
 126:    * @param buf The buffer into which the chars read will be stored.
 127:    *
 128:    * @return The number of chars read or -1 if end of stream.
 129:    *
 130:    * @exception IOException If an error occurs.
 131:    */
 132:   public int read(char buf[]) throws IOException
 133:   {
 134:     return read(buf, 0, buf.length);
 135:   }
 136: 
 137:   /**
 138:    * Reads an char from the input stream and returns it
 139:    * as an int in the range of 0-65535.  This method also will return -1 if
 140:    * the end of the stream has been reached.
 141:    * <p>
 142:    * This method will block until the char can be read.
 143:    *
 144:    * @return The char read or -1 if end of stream
 145:    *
 146:    * @exception IOException If an error occurs
 147:    */
 148:   public int read() throws IOException
 149:   {
 150:     char[] buf = new char[1];
 151:     int count = read(buf, 0, 1);
 152:     return count > 0 ? buf[0] : -1;
 153:   }
 154: 
 155:   /**
 156:    * Closes the stream.  Any futher attempts to read from the
 157:    * stream may generate an <code>IOException</code>.
 158:    *
 159:    * @exception IOException If an error occurs
 160:    */
 161:   public abstract void close() throws IOException;
 162: 
 163:   /**
 164:    * Returns a boolean that indicates whether the mark/reset
 165:    * methods are supported in this class.  Those methods can be used to
 166:    * remember a specific point in the stream and reset the stream to that
 167:    * point.
 168:    * <p>
 169:    * This method always returns <code>false</code> in this class, but
 170:    * subclasses can override this method to return <code>true</code> if they 
 171:    * support mark/reset functionality.
 172:    *
 173:    * @return <code>true</code> if mark/reset functionality is supported, 
 174:    *         <code>false</code> otherwise
 175:    *
 176:    */
 177:   public boolean markSupported()
 178:   {
 179:     return false;
 180:   }
 181: 
 182:   /**
 183:     * Marks a position in the input to which the stream can be
 184:     * "reset" by calling the <code>reset()</code> method.  The parameter
 185:     * <code>readlimit</code> is the number of chars that can be read from the 
 186:     * stream after setting the mark before the mark becomes invalid.  For
 187:     * example, if <code>mark()</code> is called with a read limit of 10, then 
 188:     * when 11 chars of data are read from the stream before the 
 189:     * <code>reset()</code> method is called, then the mark is invalid and the 
 190:     * stream object instance is not required to remember the mark.
 191:     *
 192:     * @param readLimit The number of chars that can be read before the mark 
 193:     *        becomes invalid
 194:     *
 195:     * @exception IOException If an error occurs such as mark not being 
 196:     *            supported for this class
 197:     */
 198:   public void mark(int readLimit) throws IOException
 199:   {
 200:     throw new IOException("mark not supported");
 201:   }
 202: 
 203:   /**
 204:     * Resets a stream to the point where the <code>mark()</code> 
 205:     * method was called.  Any chars that were read after the mark point was 
 206:     * set will be re-read during subsequent reads.
 207:     * <p>
 208:     * This method always throws an IOException in this class, but subclasses
 209:     * can override this method if they provide mark/reset functionality.
 210:     *
 211:     * @exception IOException Always thrown for this class
 212:     */
 213:   public void reset() throws IOException
 214:   {
 215:     throw new IOException("reset not supported");
 216:   }
 217: 
 218:   /**
 219:     * Determines whether or not this stream is ready to be
 220:     * read.  If it returns <code>false</code> the stream may block if a
 221:     * read is attempted, but it is not guaranteed to do so.
 222:     * <p>
 223:     * This method always returns <code>false</code> in this class
 224:     *
 225:     * @return <code>true</code> if the stream is ready to be read, 
 226:     * <code>false</code> otherwise.
 227:     *
 228:     * @exception IOException If an error occurs
 229:     */
 230:   public boolean ready() throws IOException
 231:   {
 232:     return false;
 233:   }
 234: 
 235:   /**
 236:     * Skips the specified number of chars in the stream.  It
 237:     * returns the actual number of chars skipped, which may be less than the
 238:     * requested amount.
 239:     * <p>
 240:     * This method reads and discards chars into a 256 char array until the
 241:     * specified number of chars were skipped or until either the end of stream
 242:     * is reached or a read attempt returns a short count.  Subclasses can
 243:     * override this method to provide a more efficient implementation where
 244:     * one exists.
 245:     *
 246:     * @param count The requested number of chars to skip
 247:     *
 248:     * @return The actual number of chars skipped.
 249:     *
 250:     * @exception IOException If an error occurs
 251:     */
 252:   public long skip(long count) throws IOException
 253:   {
 254:     if (count <= 0)
 255:       return 0;
 256:     int bsize = count > 1024 ? 1024 : (int) count;
 257:     char[] buffer = new char[bsize];
 258:     long todo = count;
 259:     synchronized (lock)
 260:     {
 261:       while (todo > 0)
 262:     {
 263:       int skipped = read(buffer, 0, bsize > todo ? (int) todo : bsize);
 264:       if (skipped <= 0)
 265:         break;
 266:       todo -= skipped;
 267:     }
 268:     }
 269:     return count - todo;
 270:   }
 271: }