1 /*
   2  * Copyright (c) 1996, 2013, 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 import java.nio.charset.Charset;
  29 import java.nio.charset.CharsetDecoder;
  30 import sun.nio.cs.StreamDecoder;
  31 
  32 
  33 /**
  34  * An InputStreamReader is a bridge from byte streams to character streams: It
  35  * reads bytes and decodes them into characters using a specified {@link
  36  * java.nio.charset.Charset charset}.  The charset that it uses
  37  * may be specified by name or may be given explicitly, or the platform's
  38  * default charset may be accepted.
  39  *
  40  * <p> Each invocation of one of an InputStreamReader's read() methods may
  41  * cause one or more bytes to be read from the underlying byte-input stream.
  42  * To enable the efficient conversion of bytes to characters, more bytes may
  43  * be read ahead from the underlying stream than are necessary to satisfy the
  44  * current read operation.
  45  *
  46  * <p> For top efficiency, consider wrapping an InputStreamReader within a
  47  * BufferedReader.  For example:
  48  *
  49  * <pre>
  50  * BufferedReader in
  51  *   = new BufferedReader(new InputStreamReader(System.in));
  52  * </pre>
  53  *
  54  * @see BufferedReader
  55  * @see InputStream
  56  * @see java.nio.charset.Charset
  57  *
  58  * @author      Mark Reinhold
  59  * @since       1.1
  60  */
  61 
  62 public class InputStreamReader extends Reader {
  63 
  64     private final StreamDecoder sd;
  65 
  66     /**
  67      * Creates an InputStreamReader that uses the default charset.
  68      *
  69      * @param  in   An InputStream
  70      */
  71     public InputStreamReader(InputStream in) {
  72         super(in);
  73         try {
  74             sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## check lock object
  75         } catch (UnsupportedEncodingException e) {
  76             // The default encoding should always be available
  77             throw new Error(e);
  78         }
  79     }
  80 
  81     /**
  82      * Creates an InputStreamReader that uses the named charset.
  83      *
  84      * @param  in
  85      *         An InputStream
  86      *
  87      * @param  charsetName
  88      *         The name of a supported
  89      *         {@link java.nio.charset.Charset charset}
  90      *
  91      * @exception  UnsupportedEncodingException
  92      *             If the named charset is not supported
  93      */
  94     public InputStreamReader(InputStream in, String charsetName)
  95         throws UnsupportedEncodingException
  96     {
  97         super(in);
  98         if (charsetName == null)
  99             throw new NullPointerException("charsetName");
 100         sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
 101     }
 102 
 103     /**
 104      * Creates an InputStreamReader that uses the given charset.
 105      *
 106      * @param  in       An InputStream
 107      * @param  cs       A charset
 108      *
 109      * @since 1.4
 110      * @spec JSR-51
 111      */
 112     public InputStreamReader(InputStream in, Charset cs) {
 113         super(in);
 114         if (cs == null)
 115             throw new NullPointerException("charset");
 116         sd = StreamDecoder.forInputStreamReader(in, this, cs);
 117     }
 118 
 119     /**
 120      * Creates an InputStreamReader that uses the given charset decoder.
 121      *
 122      * @param  in       An InputStream
 123      * @param  dec      A charset decoder
 124      *
 125      * @since 1.4
 126      * @spec JSR-51
 127      */
 128     public InputStreamReader(InputStream in, CharsetDecoder dec) {
 129         super(in);
 130         if (dec == null)
 131             throw new NullPointerException("charset decoder");
 132         sd = StreamDecoder.forInputStreamReader(in, this, dec);
 133     }
 134 
 135     /**
 136      * Returns the name of the character encoding being used by this stream.
 137      *
 138      * <p> If the encoding has an historical name then that name is returned;
 139      * otherwise the encoding's canonical name is returned.
 140      *
 141      * <p> If this instance was created with the {@link
 142      * #InputStreamReader(InputStream, String)} constructor then the returned
 143      * name, being unique for the encoding, may differ from the name passed to
 144      * the constructor. This method will return <code>null</code> if the
 145      * stream has been closed.
 146      * </p>
 147      * @return The historical name of this encoding, or
 148      *         <code>null</code> if the stream has been closed
 149      *
 150      * @see java.nio.charset.Charset
 151      *
 152      * @revised 1.4
 153      * @spec JSR-51
 154      */
 155     public String getEncoding() {
 156         return sd.getEncoding();
 157     }
 158 
 159     /**
 160      * Reads a single character.
 161      *
 162      * @return The character read, or -1 if the end of the stream has been
 163      *         reached
 164      *
 165      * @exception  IOException  If an I/O error occurs
 166      */
 167     public int read() throws IOException {
 168         return sd.read();
 169     }
 170 
 171     /**
 172      * Reads characters into a portion of an array.
 173      *
 174      * @param      cbuf     Destination buffer
 175      * @param      offset   Offset at which to start storing characters
 176      * @param      length   Maximum number of characters to read
 177      *
 178      * @return     The number of characters read, or -1 if the end of the
 179      *             stream has been reached
 180      *
 181      * @exception  IOException  If an I/O error occurs
 182      */
 183     public int read(char cbuf[], int offset, int length) throws IOException {
 184         return sd.read(cbuf, offset, length);
 185     }
 186 
 187     /**
 188      * Tells whether this stream is ready to be read.  An InputStreamReader is
 189      * ready if its input buffer is not empty, or if bytes are available to be
 190      * read from the underlying byte stream.
 191      *
 192      * @exception  IOException  If an I/O error occurs
 193      */
 194     public boolean ready() throws IOException {
 195         return sd.ready();
 196     }
 197 
 198     public void close() throws IOException {
 199         sd.close();
 200     }
 201 }