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 */ Reader()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 */ Reader(Object lock)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 */ read(char buf[], int offset, int count)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 */ read(char buf[])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 */ read()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 */ read(CharBuffer buffer)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 */ close()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 */ markSupported()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 */ mark(int readLimit)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 */ reset()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 */ ready()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 */ skip(long count)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 } 287