1 /*
   2  * Copyright (c) 1996, 2006, 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 /**
  30  * Abstract class for reading character streams.  The only methods that a
  31  * subclass must implement are read(char[], int, int) and close().  Most
  32  * subclasses, however, will override some of the methods defined here in order
  33  * to provide higher efficiency, additional functionality, or both.
  34  *
  35  *
  36  * @see BufferedReader
  37  * @see   LineNumberReader
  38  * @see CharArrayReader
  39  * @see InputStreamReader
  40  * @see   FileReader
  41  * @see FilterReader
  42  * @see   PushbackReader
  43  * @see PipedReader
  44  * @see StringReader
  45  * @see Writer
  46  *
  47  * @author      Mark Reinhold
  48  * @since       JDK1.1
  49  */
  50 
  51 public abstract class Reader implements Readable, Closeable {
  52 
  53     /**
  54      * The object used to synchronize operations on this stream.  For
  55      * efficiency, a character-stream object may use an object other than
  56      * itself to protect critical sections.  A subclass should therefore use
  57      * the object in this field rather than <tt>this</tt> or a synchronized
  58      * method.
  59      */
  60     protected Object lock;
  61 
  62     /**
  63      * Creates a new character-stream reader whose critical sections will
  64      * synchronize on the reader itself.
  65      */
  66     protected Reader() {
  67         this.lock = this;
  68     }
  69 
  70     /**
  71      * Creates a new character-stream reader whose critical sections will
  72      * synchronize on the given object.
  73      *
  74      * @param lock  The Object to synchronize on.
  75      */
  76     protected Reader(Object lock) {
  77         if (lock == null) {
  78             throw new NullPointerException();
  79         }
  80         this.lock = lock;
  81     }
  82 
  83     /**
  84      * Attempts to read characters into the specified character buffer.
  85      * The buffer is used as a repository of characters as-is: the only
  86      * changes made are the results of a put operation. No flipping or
  87      * rewinding of the buffer is performed.
  88      *
  89      * @param target the buffer to read characters into
  90      * @return The number of characters added to the buffer, or
  91      *         -1 if this source of characters is at its end
  92      * @throws IOException if an I/O error occurs
  93      * @throws NullPointerException if target is null
  94      * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
  95      * @since 1.5
  96      */
  97     public int read(java.nio.CharBuffer target) throws IOException {
  98         int len = target.remaining();
  99         char[] cbuf = new char[len];
 100         int n = read(cbuf, 0, len);
 101         if (n > 0)
 102             target.put(cbuf, 0, n);
 103         return n;
 104     }
 105 
 106     /**
 107      * Reads a single character.  This method will block until a character is
 108      * available, an I/O error occurs, or the end of the stream is reached.
 109      *
 110      * <p> Subclasses that intend to support efficient single-character input
 111      * should override this method.
 112      *
 113      * @return     The character read, as an integer in the range 0 to 65535
 114      *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
 115      *             been reached
 116      *
 117      * @exception  IOException  If an I/O error occurs
 118      */
 119     public int read() throws IOException {
 120         char cb[] = new char[1];
 121         if (read(cb, 0, 1) == -1)
 122             return -1;
 123         else
 124             return cb[0];
 125     }
 126 
 127     /**
 128      * Reads characters into an array.  This method will block until some input
 129      * is available, an I/O error occurs, or the end of the stream is reached.
 130      *
 131      * @param       cbuf  Destination buffer
 132      *
 133      * @return      The number of characters read, or -1
 134      *              if the end of the stream
 135      *              has been reached
 136      *
 137      * @exception   IOException  If an I/O error occurs
 138      */
 139     public int read(char cbuf[]) throws IOException {
 140         return read(cbuf, 0, cbuf.length);
 141     }
 142 
 143     /**
 144      * Reads characters into a portion of an array.  This method will block
 145      * until some input is available, an I/O error occurs, or the end of the
 146      * stream is reached.
 147      *
 148      * @param      cbuf  Destination buffer
 149      * @param      off   Offset at which to start storing characters
 150      * @param      len   Maximum number of characters to read
 151      *
 152      * @return     The number of characters read, or -1 if the end of the
 153      *             stream has been reached
 154      *
 155      * @exception  IOException  If an I/O error occurs
 156      */
 157     abstract public int read(char cbuf[], int off, int len) throws IOException;
 158 
 159     /** Maximum skip-buffer size */
 160     private static final int maxSkipBufferSize = 8192;
 161 
 162     /** Skip buffer, null until allocated */
 163     private char skipBuffer[] = null;
 164 
 165     /**
 166      * Skips characters.  This method will block until some characters are
 167      * available, an I/O error occurs, or the end of the stream is reached.
 168      *
 169      * @param  n  The number of characters to skip
 170      *
 171      * @return    The number of characters actually skipped
 172      *
 173      * @exception  IllegalArgumentException  If <code>n</code> is negative.
 174      * @exception  IOException  If an I/O error occurs
 175      */
 176     public long skip(long n) throws IOException {
 177         if (n < 0L)
 178             throw new IllegalArgumentException("skip value is negative");
 179         int nn = (int) Math.min(n, maxSkipBufferSize);
 180         synchronized (lock) {
 181             if ((skipBuffer == null) || (skipBuffer.length < nn))
 182                 skipBuffer = new char[nn];
 183             long r = n;
 184             while (r > 0) {
 185                 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
 186                 if (nc == -1)
 187                     break;
 188                 r -= nc;
 189             }
 190             return n - r;
 191         }
 192     }
 193 
 194     /**
 195      * Tells whether this stream is ready to be read.
 196      *
 197      * @return True if the next read() is guaranteed not to block for input,
 198      * false otherwise.  Note that returning false does not guarantee that the
 199      * next read will block.
 200      *
 201      * @exception  IOException  If an I/O error occurs
 202      */
 203     public boolean ready() throws IOException {
 204         return false;
 205     }
 206 
 207     /**
 208      * Tells whether this stream supports the mark() operation. The default
 209      * implementation always returns false. Subclasses should override this
 210      * method.
 211      *
 212      * @return true if and only if this stream supports the mark operation.
 213      */
 214     public boolean markSupported() {
 215         return false;
 216     }
 217 
 218     /**
 219      * Marks the present position in the stream.  Subsequent calls to reset()
 220      * will attempt to reposition the stream to this point.  Not all
 221      * character-input streams support the mark() operation.
 222      *
 223      * @param  readAheadLimit  Limit on the number of characters that may be
 224      *                         read while still preserving the mark.  After
 225      *                         reading this many characters, attempting to
 226      *                         reset the stream may fail.
 227      *
 228      * @exception  IOException  If the stream does not support mark(),
 229      *                          or if some other I/O error occurs
 230      */
 231     public void mark(int readAheadLimit) throws IOException {
 232         throw new IOException("mark() not supported");
 233     }
 234 
 235     /**
 236      * Resets the stream.  If the stream has been marked, then attempt to
 237      * reposition it at the mark.  If the stream has not been marked, then
 238      * attempt to reset it in some way appropriate to the particular stream,
 239      * for example by repositioning it to its starting point.  Not all
 240      * character-input streams support the reset() operation, and some support
 241      * reset() without supporting mark().
 242      *
 243      * @exception  IOException  If the stream has not been marked,
 244      *                          or if the mark has been invalidated,
 245      *                          or if the stream does not support reset(),
 246      *                          or if some other I/O error occurs
 247      */
 248     public void reset() throws IOException {
 249         throw new IOException("reset() not supported");
 250     }
 251 
 252     /**
 253      * Closes the stream and releases any system resources associated with
 254      * it.  Once the stream has been closed, further read(), ready(),
 255      * mark(), reset(), or skip() invocations will throw an IOException.
 256      * Closing a previously closed stream has no effect.
 257      *
 258      * @exception  IOException  If an I/O error occurs
 259      */
 260      abstract public void close() throws IOException;
 261 
 262 }