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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       JDK1.1
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      */
InputStreamReader(InputStream in)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      */
InputStreamReader(InputStream in, String charsetName)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      */
InputStreamReader(InputStream in, Charset cs)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      */
InputStreamReader(InputStream in, CharsetDecoder dec)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      */
getEncoding()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      */
read()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      */
read(char cbuf[], int offset, int length)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      */
ready()194     public boolean ready() throws IOException {
195         return sd.ready();
196     }
197 
close()198     public void close() throws IOException {
199         sd.close();
200     }
201 }
202