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    1   /*
    2    * Copyright (c) 1994, 2010, 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    * A <code>FilterInputStream</code> contains
   30    * some other input stream, which it uses as
   31    * its  basic source of data, possibly transforming
   32    * the data along the way or providing  additional
   33    * functionality. The class <code>FilterInputStream</code>
   34    * itself simply overrides all  methods of
   35    * <code>InputStream</code> with versions that
   36    * pass all requests to the contained  input
   37    * stream. Subclasses of <code>FilterInputStream</code>
   38    * may further override some of  these methods
   39    * and may also provide additional methods
   40    * and fields.
   41    *
   42    * @author  Jonathan Payne
   43    * @since   JDK1.0
   44    */
   45   public
   46   class FilterInputStream extends InputStream {
   47       /**
   48        * The input stream to be filtered.
   49        */
   50       protected volatile InputStream in;
   51   
   52       /**
   53        * Creates a <code>FilterInputStream</code>
   54        * by assigning the  argument <code>in</code>
   55        * to the field <code>this.in</code> so as
   56        * to remember it for later use.
   57        *
   58        * @param   in   the underlying input stream, or <code>null</code> if
   59        *          this instance is to be created without an underlying stream.
   60        */
   61       protected FilterInputStream(InputStream in) {
   62           this.in = in;
   63       }
   64   
   65       /**
   66        * Reads the next byte of data from this input stream. The value
   67        * byte is returned as an <code>int</code> in the range
   68        * <code>0</code> to <code>255</code>. If no byte is available
   69        * because the end of the stream has been reached, the value
   70        * <code>-1</code> is returned. This method blocks until input data
   71        * is available, the end of the stream is detected, or an exception
   72        * is thrown.
   73        * <p>
   74        * This method
   75        * simply performs <code>in.read()</code> and returns the result.
   76        *
   77        * @return     the next byte of data, or <code>-1</code> if the end of the
   78        *             stream is reached.
   79        * @exception  IOException  if an I/O error occurs.
   80        * @see        java.io.FilterInputStream#in
   81        */
   82       public int read() throws IOException {
   83           return in.read();
   84       }
   85   
   86       /**
   87        * Reads up to <code>byte.length</code> bytes of data from this
   88        * input stream into an array of bytes. This method blocks until some
   89        * input is available.
   90        * <p>
   91        * This method simply performs the call
   92        * <code>read(b, 0, b.length)</code> and returns
   93        * the  result. It is important that it does
   94        * <i>not</i> do <code>in.read(b)</code> instead;
   95        * certain subclasses of  <code>FilterInputStream</code>
   96        * depend on the implementation strategy actually
   97        * used.
   98        *
   99        * @param      b   the buffer into which the data is read.
  100        * @return     the total number of bytes read into the buffer, or
  101        *             <code>-1</code> if there is no more data because the end of
  102        *             the stream has been reached.
  103        * @exception  IOException  if an I/O error occurs.
  104        * @see        java.io.FilterInputStream#read(byte[], int, int)
  105        */
  106       public int read(byte b[]) throws IOException {
  107           return read(b, 0, b.length);
  108       }
  109   
  110       /**
  111        * Reads up to <code>len</code> bytes of data from this input stream
  112        * into an array of bytes. If <code>len</code> is not zero, the method
  113        * blocks until some input is available; otherwise, no
  114        * bytes are read and <code>0</code> is returned.
  115        * <p>
  116        * This method simply performs <code>in.read(b, off, len)</code>
  117        * and returns the result.
  118        *
  119        * @param      b     the buffer into which the data is read.
  120        * @param      off   the start offset in the destination array <code>b</code>
  121        * @param      len   the maximum number of bytes read.
  122        * @return     the total number of bytes read into the buffer, or
  123        *             <code>-1</code> if there is no more data because the end of
  124        *             the stream has been reached.
  125        * @exception  NullPointerException If <code>b</code> is <code>null</code>.
  126        * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
  127        * <code>len</code> is negative, or <code>len</code> is greater than
  128        * <code>b.length - off</code>
  129        * @exception  IOException  if an I/O error occurs.
  130        * @see        java.io.FilterInputStream#in
  131        */
  132       public int read(byte b[], int off, int len) throws IOException {
  133           return in.read(b, off, len);
  134       }
  135   
  136       /**
  137        * Skips over and discards <code>n</code> bytes of data from the
  138        * input stream. The <code>skip</code> method may, for a variety of
  139        * reasons, end up skipping over some smaller number of bytes,
  140        * possibly <code>0</code>. The actual number of bytes skipped is
  141        * returned.
  142        * <p>
  143        * This method simply performs <code>in.skip(n)</code>.
  144        *
  145        * @param      n   the number of bytes to be skipped.
  146        * @return     the actual number of bytes skipped.
  147        * @exception  IOException  if the stream does not support seek,
  148        *                          or if some other I/O error occurs.
  149        */
  150       public long skip(long n) throws IOException {
  151           return in.skip(n);
  152       }
  153   
  154       /**
  155        * Returns an estimate of the number of bytes that can be read (or
  156        * skipped over) from this input stream without blocking by the next
  157        * caller of a method for this input stream. The next caller might be
  158        * the same thread or another thread.  A single read or skip of this
  159        * many bytes will not block, but may read or skip fewer bytes.
  160        * <p>
  161        * This method returns the result of {@link #in in}.available().
  162        *
  163        * @return     an estimate of the number of bytes that can be read (or skipped
  164        *             over) from this input stream without blocking.
  165        * @exception  IOException  if an I/O error occurs.
  166        */
  167       public int available() throws IOException {
  168           return in.available();
  169       }
  170   
  171       /**
  172        * Closes this input stream and releases any system resources
  173        * associated with the stream.
  174        * This
  175        * method simply performs <code>in.close()</code>.
  176        *
  177        * @exception  IOException  if an I/O error occurs.
  178        * @see        java.io.FilterInputStream#in
  179        */
  180       public void close() throws IOException {
  181           in.close();
  182       }
  183   
  184       /**
  185        * Marks the current position in this input stream. A subsequent
  186        * call to the <code>reset</code> method repositions this stream at
  187        * the last marked position so that subsequent reads re-read the same bytes.
  188        * <p>
  189        * The <code>readlimit</code> argument tells this input stream to
  190        * allow that many bytes to be read before the mark position gets
  191        * invalidated.
  192        * <p>
  193        * This method simply performs <code>in.mark(readlimit)</code>.
  194        *
  195        * @param   readlimit   the maximum limit of bytes that can be read before
  196        *                      the mark position becomes invalid.
  197        * @see     java.io.FilterInputStream#in
  198        * @see     java.io.FilterInputStream#reset()
  199        */
  200       public synchronized void mark(int readlimit) {
  201           in.mark(readlimit);
  202       }
  203   
  204       /**
  205        * Repositions this stream to the position at the time the
  206        * <code>mark</code> method was last called on this input stream.
  207        * <p>
  208        * This method
  209        * simply performs <code>in.reset()</code>.
  210        * <p>
  211        * Stream marks are intended to be used in
  212        * situations where you need to read ahead a little to see what's in
  213        * the stream. Often this is most easily done by invoking some
  214        * general parser. If the stream is of the type handled by the
  215        * parse, it just chugs along happily. If the stream is not of
  216        * that type, the parser should toss an exception when it fails.
  217        * If this happens within readlimit bytes, it allows the outer
  218        * code to reset the stream and try another parser.
  219        *
  220        * @exception  IOException  if the stream has not been marked or if the
  221        *               mark has been invalidated.
  222        * @see        java.io.FilterInputStream#in
  223        * @see        java.io.FilterInputStream#mark(int)
  224        */
  225       public synchronized void reset() throws IOException {
  226           in.reset();
  227       }
  228   
  229       /**
  230        * Tests if this input stream supports the <code>mark</code>
  231        * and <code>reset</code> methods.
  232        * This method
  233        * simply performs <code>in.markSupported()</code>.
  234        *
  235        * @return  <code>true</code> if this stream type supports the
  236        *          <code>mark</code> and <code>reset</code> method;
  237        *          <code>false</code> otherwise.
  238        * @see     java.io.FilterInputStream#in
  239        * @see     java.io.InputStream#mark(int)
  240        * @see     java.io.InputStream#reset()
  241        */
  242       public boolean markSupported() {
  243           return in.markSupported();
  244       }
  245   }

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