1 /* 2 * Copyright (c) 1996, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.io; 27 28 29 import java.nio.CharBuffer; 30 import java.util.Objects; 31 32 /** 33 * Abstract class for reading character streams. The only methods that a 34 * subclass must implement are read(char[], int, int) and close(). Most 35 * subclasses, however, will override some of the methods defined here in order 36 * to provide higher efficiency, additional functionality, or both. 37 * 38 * 39 * @see BufferedReader 40 * @see LineNumberReader 41 * @see CharArrayReader 42 * @see InputStreamReader 43 * @see FileReader 44 * @see FilterReader 45 * @see PushbackReader 46 * @see PipedReader 47 * @see StringReader 48 * @see Writer 49 * 50 * @author Mark Reinhold 51 * @since 1.1 52 */ 53 54 public abstract class Reader implements Readable, Closeable { 55 56 private static final int TRANSFER_BUFFER_SIZE = 8192; 57 58 /** 59 * Returns a new {@code Reader} that reads no characters. The returned 60 * stream is initially open. The stream is closed by calling the 61 * {@code close()} method. Subsequent calls to {@code close()} have no 62 * effect. 63 * 64 * <p> While the stream is open, the {@code read()}, {@code read(char[])}, 65 * {@code read(char[], int, int)}, {@code read(Charbuffer)}, {@code 66 * ready())}, {@code skip(long)}, and {@code transferTo()} methods all 67 * behave as if end of stream has been reached. After the stream has been 68 * closed, these methods all throw {@code IOException}. 69 * 70 * <p> The {@code markSupported()} method returns {@code false}. The 71 * {@code mark()} method does nothing, and the {@code reset()} method 72 * throws {@code IOException}. 73 * 74 * <p> The {@link #lock object} used to synchronize operations on the 75 * returned {@code Reader} is not specified. 76 * 77 * @return a {@code Reader} which reads no characters 78 * 79 * @since 11 80 */ 81 public static Reader nullReader() { 82 return new Reader() { 83 private volatile boolean closed; 84 85 private void ensureOpen() throws IOException { 86 if (closed) { 87 throw new IOException("Stream closed"); 88 } 89 } 90 91 @Override 92 public int read() throws IOException { 93 ensureOpen(); 94 return -1; 95 } 96 97 @Override 98 public int read(char[] cbuf, int off, int len) throws IOException { 99 Objects.checkFromIndexSize(off, len, cbuf.length); 100 ensureOpen(); 101 if (len == 0) { 102 return 0; 103 } 104 return -1; 105 } 106 107 @Override 108 public int read(CharBuffer target) throws IOException { 109 Objects.requireNonNull(target); 110 ensureOpen(); 111 if (target.hasRemaining()) { 112 return -1; 113 } 114 return 0; 115 } 116 117 @Override 118 public long skip(long n) throws IOException { 119 ensureOpen(); 120 return 0L; 121 } 122 123 @Override 124 public long transferTo(Writer out) throws IOException { 125 Objects.requireNonNull(out); 126 ensureOpen(); 127 return 0L; 128 } 129 130 @Override 131 public void close() { 132 closed = true; 133 } 134 }; 135 } 136 137 /** 138 * The object used to synchronize operations on this stream. For 139 * efficiency, a character-stream object may use an object other than 140 * itself to protect critical sections. A subclass should therefore use 141 * the object in this field rather than {@code this} or a synchronized 142 * method. 143 */ 144 protected Object lock; 145 146 /** 147 * Creates a new character-stream reader whose critical sections will 148 * synchronize on the reader itself. 149 */ 150 protected Reader() { 151 this.lock = this; 152 } 153 154 /** 155 * Creates a new character-stream reader whose critical sections will 156 * synchronize on the given object. 157 * 158 * @param lock The Object to synchronize on. 159 */ 160 protected Reader(Object lock) { 161 if (lock == null) { 162 throw new NullPointerException(); 163 } 164 this.lock = lock; 165 } 166 167 /** 168 * Attempts to read characters into the specified character buffer. 169 * The buffer is used as a repository of characters as-is: the only 170 * changes made are the results of a put operation. No flipping or 171 * rewinding of the buffer is performed. 172 * 173 * @param target the buffer to read characters into 174 * @return The number of characters added to the buffer, or 175 * -1 if this source of characters is at its end 176 * @throws IOException if an I/O error occurs 177 * @throws NullPointerException if target is null 178 * @throws java.nio.ReadOnlyBufferException if target is a read only buffer 179 * @since 1.5 180 */ 181 public int read(java.nio.CharBuffer target) throws IOException { 182 int len = target.remaining(); 183 char[] cbuf = new char[len]; 184 int n = read(cbuf, 0, len); 185 if (n > 0) 186 target.put(cbuf, 0, n); 187 return n; 188 } 189 190 /** 191 * Reads a single character. This method will block until a character is 192 * available, an I/O error occurs, or the end of the stream is reached. 193 * 194 * <p> Subclasses that intend to support efficient single-character input 195 * should override this method. 196 * 197 * @return The character read, as an integer in the range 0 to 65535 198 * ({@code 0x00-0xffff}), or -1 if the end of the stream has 199 * been reached 200 * 201 * @exception IOException If an I/O error occurs 202 */ 203 public int read() throws IOException { 204 char cb[] = new char[1]; 205 if (read(cb, 0, 1) == -1) 206 return -1; 207 else 208 return cb[0]; 209 } 210 211 /** 212 * Reads characters into an array. This method will block until some input 213 * is available, an I/O error occurs, or the end of the stream is reached. 214 * 215 * @param cbuf Destination buffer 216 * 217 * @return The number of characters read, or -1 218 * if the end of the stream 219 * has been reached 220 * 221 * @exception IOException If an I/O error occurs 222 */ 223 public int read(char cbuf[]) throws IOException { 224 return read(cbuf, 0, cbuf.length); 225 } 226 227 /** 228 * Reads characters into a portion of an array. This method will block 229 * until some input is available, an I/O error occurs, or the end of the 230 * stream is reached. 231 * 232 * @param cbuf Destination buffer 233 * @param off Offset at which to start storing characters 234 * @param len Maximum number of characters to read 235 * 236 * @return The number of characters read, or -1 if the end of the 237 * stream has been reached 238 * 239 * @exception IOException If an I/O error occurs 240 * @exception IndexOutOfBoundsException 241 * If {@code off} is negative, or {@code len} is negative, 242 * or {@code len} is greater than {@code cbuf.length - off} 243 */ 244 public abstract int read(char cbuf[], int off, int len) throws IOException; 245 246 /** Maximum skip-buffer size */ 247 private static final int maxSkipBufferSize = 8192; 248 249 /** Skip buffer, null until allocated */ 250 private char skipBuffer[] = null; 251 252 /** 253 * Skips characters. This method will block until some characters are 254 * available, an I/O error occurs, or the end of the stream is reached. 255 * 256 * @param n The number of characters to skip 257 * 258 * @return The number of characters actually skipped 259 * 260 * @exception IllegalArgumentException If <code>n</code> is negative. 261 * @exception IOException If an I/O error occurs 262 */ 263 public long skip(long n) throws IOException { 264 if (n < 0L) 265 throw new IllegalArgumentException("skip value is negative"); 266 int nn = (int) Math.min(n, maxSkipBufferSize); 267 synchronized (lock) { 268 if ((skipBuffer == null) || (skipBuffer.length < nn)) 269 skipBuffer = new char[nn]; 270 long r = n; 271 while (r > 0) { 272 int nc = read(skipBuffer, 0, (int)Math.min(r, nn)); 273 if (nc == -1) 274 break; 275 r -= nc; 276 } 277 return n - r; 278 } 279 } 280 281 /** 282 * Tells whether this stream is ready to be read. 283 * 284 * @return True if the next read() is guaranteed not to block for input, 285 * false otherwise. Note that returning false does not guarantee that the 286 * next read will block. 287 * 288 * @exception IOException If an I/O error occurs 289 */ 290 public boolean ready() throws IOException { 291 return false; 292 } 293 294 /** 295 * Tells whether this stream supports the mark() operation. The default 296 * implementation always returns false. Subclasses should override this 297 * method. 298 * 299 * @return true if and only if this stream supports the mark operation. 300 */ 301 public boolean markSupported() { 302 return false; 303 } 304 305 /** 306 * Marks the present position in the stream. Subsequent calls to reset() 307 * will attempt to reposition the stream to this point. Not all 308 * character-input streams support the mark() operation. 309 * 310 * @param readAheadLimit Limit on the number of characters that may be 311 * read while still preserving the mark. After 312 * reading this many characters, attempting to 313 * reset the stream may fail. 314 * 315 * @exception IOException If the stream does not support mark(), 316 * or if some other I/O error occurs 317 */ 318 public void mark(int readAheadLimit) throws IOException { 319 throw new IOException("mark() not supported"); 320 } 321 322 /** 323 * Resets the stream. If the stream has been marked, then attempt to 324 * reposition it at the mark. If the stream has not been marked, then 325 * attempt to reset it in some way appropriate to the particular stream, 326 * for example by repositioning it to its starting point. Not all 327 * character-input streams support the reset() operation, and some support 328 * reset() without supporting mark(). 329 * 330 * @exception IOException If the stream has not been marked, 331 * or if the mark has been invalidated, 332 * or if the stream does not support reset(), 333 * or if some other I/O error occurs 334 */ 335 public void reset() throws IOException { 336 throw new IOException("reset() not supported"); 337 } 338 339 /** 340 * Closes the stream and releases any system resources associated with 341 * it. Once the stream has been closed, further read(), ready(), 342 * mark(), reset(), or skip() invocations will throw an IOException. 343 * Closing a previously closed stream has no effect. 344 * 345 * @exception IOException If an I/O error occurs 346 */ 347 public abstract void close() throws IOException; 348 349 /** 350 * Reads all characters from this reader and writes the characters to the 351 * given writer in the order that they are read. On return, this reader 352 * will be at end of the stream. This method does not close either reader 353 * or writer. 354 * <p> 355 * This method may block indefinitely reading from the reader, or 356 * writing to the writer. The behavior for the case where the reader 357 * and/or writer is <i>asynchronously closed</i>, or the thread 358 * interrupted during the transfer, is highly reader and writer 359 * specific, and therefore not specified. 360 * <p> 361 * If an I/O error occurs reading from the reader or writing to the 362 * writer, then it may do so after some characters have been read or 363 * written. Consequently the reader may not be at end of the stream and 364 * one, or both, streams may be in an inconsistent state. It is strongly 365 * recommended that both streams be promptly closed if an I/O error occurs. 366 * 367 * @param out the writer, non-null 368 * @return the number of characters transferred 369 * @throws IOException if an I/O error occurs when reading or writing 370 * @throws NullPointerException if {@code out} is {@code null} 371 * 372 * @since 10 373 */ 374 public long transferTo(Writer out) throws IOException { 375 Objects.requireNonNull(out, "out"); 376 long transferred = 0; 377 char[] buffer = new char[TRANSFER_BUFFER_SIZE]; 378 int nRead; 379 while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) { 380 out.write(buffer, 0, nRead); 381 transferred += nRead; 382 } 383 return transferred; 384 } 385 386 }