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25 
26 package java.io;
27 
28 import java.nio.CharBuffer;
29 import java.nio.charset.Charset;
30 import java.nio.charset.CharsetEncoder;
31 import sun.nio.cs.StreamEncoder;
32 
33 
34 /**
35  * An OutputStreamWriter is a bridge from character streams to byte streams:
36  * Characters written to it are encoded into bytes using a specified {@link
37  * java.nio.charset.Charset charset}.  The charset that it uses
38  * may be specified by name or may be given explicitly, or the platform's
39  * default charset may be accepted.
40  *
41  * <p> Each invocation of a write() method causes the encoding converter to be
42  * invoked on the given character(s).  The resulting bytes are accumulated in a
43  * buffer before being written to the underlying output stream.  Note that the
44  * characters passed to the write() methods are not buffered.
45  *
46  * <p> For top efficiency, consider wrapping an OutputStreamWriter within a
47  * BufferedWriter so as to avoid frequent converter invocations.  For example:
48  *
49  * <pre>
50  * Writer out
51  *   = new BufferedWriter(new OutputStreamWriter(System.out));
52  * </pre>
53  *
54  * <p> A <i>surrogate pair</i> is a character represented by a sequence of two
55  * {@code char} values: A <i>high</i> surrogate in the range '&#92;uD800' to
56  * '&#92;uDBFF' followed by a <i>low</i> surrogate in the range '&#92;uDC00' to
57  * '&#92;uDFFF'.
58  *
59  * <p> A <i>malformed surrogate element</i> is a high surrogate that is not
60  * followed by a low surrogate or a low surrogate that is not preceded by a
61  * high surrogate.
62  *
63  * <p> This class always replaces malformed surrogate elements and unmappable
64  * character sequences with the charset's default <i>substitution sequence</i>.
65  * The {@linkplain java.nio.charset.CharsetEncoder} class should be used when more
66  * control over the encoding process is required.
67  *
68  * @see BufferedWriter
69  * @see OutputStream
70  * @see java.nio.charset.Charset
71  *
72  * @author      Mark Reinhold
73  * @since       1.1
74  */
75 
76 public class OutputStreamWriter extends Writer {
77 
78     private final StreamEncoder se;
79 
80     /**
81      * Creates an OutputStreamWriter that uses the named charset.
82      *
83      * @param  out
84      *         An OutputStream
85      *
86      * @param  charsetName
87      *         The name of a supported
88      *         {@link java.nio.charset.Charset charset}
89      *
90      * @throws     UnsupportedEncodingException
91      *             If the named encoding is not supported
92      */
OutputStreamWriter(OutputStream out, String charsetName)93     public OutputStreamWriter(OutputStream out, String charsetName)
94         throws UnsupportedEncodingException
95     {
96         super(out);
97         if (charsetName == null)
98             throw new NullPointerException("charsetName");
99         se = StreamEncoder.forOutputStreamWriter(out, this, charsetName);
100     }
101 
102     /**
103      * Creates an OutputStreamWriter that uses the default character encoding.
104      *
105      * @param  out  An OutputStream
106      */
OutputStreamWriter(OutputStream out)107     public OutputStreamWriter(OutputStream out) {
108         super(out);
109         se = StreamEncoder.forOutputStreamWriter(out, this,
110                 Charset.defaultCharset());
111     }
112 
113     /**
114      * Creates an OutputStreamWriter that uses the given charset.
115      *
116      * @param  out
117      *         An OutputStream
118      *
119      * @param  cs
120      *         A charset
121      *
122      * @since 1.4
123      */
OutputStreamWriter(OutputStream out, Charset cs)124     public OutputStreamWriter(OutputStream out, Charset cs) {
125         super(out);
126         if (cs == null)
127             throw new NullPointerException("charset");
128         se = StreamEncoder.forOutputStreamWriter(out, this, cs);
129     }
130 
131     /**
132      * Creates an OutputStreamWriter that uses the given charset encoder.
133      *
134      * @param  out
135      *         An OutputStream
136      *
137      * @param  enc
138      *         A charset encoder
139      *
140      * @since 1.4
141      */
OutputStreamWriter(OutputStream out, CharsetEncoder enc)142     public OutputStreamWriter(OutputStream out, CharsetEncoder enc) {
143         super(out);
144         if (enc == null)
145             throw new NullPointerException("charset encoder");
146         se = StreamEncoder.forOutputStreamWriter(out, this, enc);
147     }
148 
149     /**
150      * Returns the name of the character encoding being used by this stream.
151      *
152      * <p> If the encoding has an historical name then that name is returned;
153      * otherwise the encoding's canonical name is returned.
154      *
155      * <p> If this instance was created with the {@link
156      * #OutputStreamWriter(OutputStream, String)} constructor then the returned
157      * name, being unique for the encoding, may differ from the name passed to
158      * the constructor.  This method may return {@code null} if the stream has
159      * been closed. </p>
160      *
161      * @return The historical name of this encoding, or possibly
162      *         {@code null} if the stream has been closed
163      *
164      * @see java.nio.charset.Charset
165      *
166      * @revised 1.4
167      */
getEncoding()168     public String getEncoding() {
169         return se.getEncoding();
170     }
171 
172     /**
173      * Flushes the output buffer to the underlying byte stream, without flushing
174      * the byte stream itself.  This method is non-private only so that it may
175      * be invoked by PrintStream.
176      */
flushBuffer()177     void flushBuffer() throws IOException {
178         se.flushBuffer();
179     }
180 
181     /**
182      * Writes a single character.
183      *
184      * @throws     IOException  If an I/O error occurs
185      */
write(int c)186     public void write(int c) throws IOException {
187         se.write(c);
188     }
189 
190     /**
191      * Writes a portion of an array of characters.
192      *
193      * @param  cbuf  Buffer of characters
194      * @param  off   Offset from which to start writing characters
195      * @param  len   Number of characters to write
196      *
197      * @throws  IndexOutOfBoundsException
198      *          If {@code off} is negative, or {@code len} is negative,
199      *          or {@code off + len} is negative or greater than the length
200      *          of the given array
201      *
202      * @throws  IOException  If an I/O error occurs
203      */
write(char cbuf[], int off, int len)204     public void write(char cbuf[], int off, int len) throws IOException {
205         se.write(cbuf, off, len);
206     }
207 
208     /**
209      * Writes a portion of a string.
210      *
211      * @param  str  A String
212      * @param  off  Offset from which to start writing characters
213      * @param  len  Number of characters to write
214      *
215      * @throws  IndexOutOfBoundsException
216      *          If {@code off} is negative, or {@code len} is negative,
217      *          or {@code off + len} is negative or greater than the length
218      *          of the given string
219      *
220      * @throws  IOException  If an I/O error occurs
221      */
write(String str, int off, int len)222     public void write(String str, int off, int len) throws IOException {
223         se.write(str, off, len);
224     }
225 
226     @Override
append(CharSequence csq, int start, int end)227     public Writer append(CharSequence csq, int start, int end) throws IOException {
228         if (csq == null) csq = "null";
229         return append(csq.subSequence(start, end));
230     }
231 
232     @Override
append(CharSequence csq)233     public Writer append(CharSequence csq) throws IOException {
234         if (csq instanceof CharBuffer) {
235             se.write((CharBuffer) csq);
236         } else {
237             se.write(String.valueOf(csq));
238         }
239         return this;
240     }
241 
242     /**
243      * Flushes the stream.
244      *
245      * @throws     IOException  If an I/O error occurs
246      */
flush()247     public void flush() throws IOException {
248         se.flush();
249     }
250 
close()251     public void close() throws IOException {
252         se.close();
253     }
254 }
255