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25 
26 package java.io;
27 
28 
29 /**
30  * Writes text to a character-output stream, buffering characters so as to
31  * provide for the efficient writing of single characters, arrays, and strings.
32  *
33  * <p> The buffer size may be specified, or the default size may be accepted.
34  * The default is large enough for most purposes.
35  *
36  * <p> A newLine() method is provided, which uses the platform's own notion of
37  * line separator as defined by the system property {@code line.separator}.
38  * Not all platforms use the newline character ('\n') to terminate lines.
39  * Calling this method to terminate each output line is therefore preferred to
40  * writing a newline character directly.
41  *
42  * <p> In general, a Writer sends its output immediately to the underlying
43  * character or byte stream.  Unless prompt output is required, it is advisable
44  * to wrap a BufferedWriter around any Writer whose write() operations may be
45  * costly, such as FileWriters and OutputStreamWriters.  For example,
46  *
47  * <pre>
48  * PrintWriter out
49  *   = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
50  * </pre>
51  *
52  * will buffer the PrintWriter's output to the file.  Without buffering, each
53  * invocation of a print() method would cause characters to be converted into
54  * bytes that would then be written immediately to the file, which can be very
55  * inefficient.
56  *
57  * @see PrintWriter
58  * @see FileWriter
59  * @see OutputStreamWriter
60  * @see java.nio.file.Files#newBufferedWriter
61  *
62  * @author      Mark Reinhold
63  * @since       1.1
64  */
65 
66 public class BufferedWriter extends Writer {
67 
68     private Writer out;
69 
70     private char cb[];
71     private int nChars, nextChar;
72 
73     private static int defaultCharBufferSize = 8192;
74 
75     /**
76      * Creates a buffered character-output stream that uses a default-sized
77      * output buffer.
78      *
79      * @param  out  A Writer
80      */
BufferedWriter(Writer out)81     public BufferedWriter(Writer out) {
82         this(out, defaultCharBufferSize);
83     }
84 
85     /**
86      * Creates a new buffered character-output stream that uses an output
87      * buffer of the given size.
88      *
89      * @param  out  A Writer
90      * @param  sz   Output-buffer size, a positive integer
91      *
92      * @exception  IllegalArgumentException  If {@code sz <= 0}
93      */
BufferedWriter(Writer out, int sz)94     public BufferedWriter(Writer out, int sz) {
95         super(out);
96         if (sz <= 0)
97             throw new IllegalArgumentException("Buffer size <= 0");
98         this.out = out;
99         cb = new char[sz];
100         nChars = sz;
101         nextChar = 0;
102     }
103 
104     /** Checks to make sure that the stream has not been closed */
ensureOpen()105     private void ensureOpen() throws IOException {
106         if (out == null)
107             throw new IOException("Stream closed");
108     }
109 
110     /**
111      * Flushes the output buffer to the underlying character stream, without
112      * flushing the stream itself.  This method is non-private only so that it
113      * may be invoked by PrintStream.
114      */
flushBuffer()115     void flushBuffer() throws IOException {
116         synchronized (lock) {
117             ensureOpen();
118             if (nextChar == 0)
119                 return;
120             out.write(cb, 0, nextChar);
121             nextChar = 0;
122         }
123     }
124 
125     /**
126      * Writes a single character.
127      *
128      * @exception  IOException  If an I/O error occurs
129      */
write(int c)130     public void write(int c) throws IOException {
131         synchronized (lock) {
132             ensureOpen();
133             if (nextChar >= nChars)
134                 flushBuffer();
135             cb[nextChar++] = (char) c;
136         }
137     }
138 
139     /**
140      * Our own little min method, to avoid loading java.lang.Math if we've run
141      * out of file descriptors and we're trying to print a stack trace.
142      */
min(int a, int b)143     private int min(int a, int b) {
144         if (a < b) return a;
145         return b;
146     }
147 
148     /**
149      * Writes a portion of an array of characters.
150      *
151      * <p> Ordinarily this method stores characters from the given array into
152      * this stream's buffer, flushing the buffer to the underlying stream as
153      * needed.  If the requested length is at least as large as the buffer,
154      * however, then this method will flush the buffer and write the characters
155      * directly to the underlying stream.  Thus redundant
156      * {@code BufferedWriter}s will not copy data unnecessarily.
157      *
158      * @param  cbuf  A character array
159      * @param  off   Offset from which to start reading characters
160      * @param  len   Number of characters to write
161      *
162      * @throws  IndexOutOfBoundsException
163      *          If {@code off} is negative, or {@code len} is negative,
164      *          or {@code off + len} is negative or greater than the length
165      *          of the given array
166      *
167      * @throws  IOException  If an I/O error occurs
168      */
write(char cbuf[], int off, int len)169     public void write(char cbuf[], int off, int len) throws IOException {
170         synchronized (lock) {
171             ensureOpen();
172             if ((off < 0) || (off > cbuf.length) || (len < 0) ||
173                 ((off + len) > cbuf.length) || ((off + len) < 0)) {
174                 throw new IndexOutOfBoundsException();
175             } else if (len == 0) {
176                 return;
177             }
178 
179             if (len >= nChars) {
180                 /* If the request length exceeds the size of the output buffer,
181                    flush the buffer and then write the data directly.  In this
182                    way buffered streams will cascade harmlessly. */
183                 flushBuffer();
184                 out.write(cbuf, off, len);
185                 return;
186             }
187 
188             int b = off, t = off + len;
189             while (b < t) {
190                 int d = min(nChars - nextChar, t - b);
191                 System.arraycopy(cbuf, b, cb, nextChar, d);
192                 b += d;
193                 nextChar += d;
194                 if (nextChar >= nChars)
195                     flushBuffer();
196             }
197         }
198     }
199 
200     /**
201      * Writes a portion of a String.
202      *
203      * @implSpec
204      * While the specification of this method in the
205      * {@linkplain java.io.Writer#write(java.lang.String,int,int) superclass}
206      * recommends that an {@link IndexOutOfBoundsException} be thrown
207      * if {@code len} is negative or {@code off + len} is negative,
208      * the implementation in this class does not throw such an exception in
209      * these cases but instead simply writes no characters.
210      *
211      * @param  s     String to be written
212      * @param  off   Offset from which to start reading characters
213      * @param  len   Number of characters to be written
214      *
215      * @throws  IndexOutOfBoundsException
216      *          If {@code off} is negative,
217      *          or {@code off + len} is greater than the length
218      *          of the given string
219      *
220      * @throws  IOException  If an I/O error occurs
221      */
write(String s, int off, int len)222     public void write(String s, int off, int len) throws IOException {
223         synchronized (lock) {
224             ensureOpen();
225 
226             int b = off, t = off + len;
227             while (b < t) {
228                 int d = min(nChars - nextChar, t - b);
229                 s.getChars(b, b + d, cb, nextChar);
230                 b += d;
231                 nextChar += d;
232                 if (nextChar >= nChars)
233                     flushBuffer();
234             }
235         }
236     }
237 
238     /**
239      * Writes a line separator.  The line separator string is defined by the
240      * system property {@code line.separator}, and is not necessarily a single
241      * newline ('\n') character.
242      *
243      * @exception  IOException  If an I/O error occurs
244      */
newLine()245     public void newLine() throws IOException {
246         write(System.lineSeparator());
247     }
248 
249     /**
250      * Flushes the stream.
251      *
252      * @exception  IOException  If an I/O error occurs
253      */
flush()254     public void flush() throws IOException {
255         synchronized (lock) {
256             flushBuffer();
257             out.flush();
258         }
259     }
260 
261     @SuppressWarnings("try")
close()262     public void close() throws IOException {
263         synchronized (lock) {
264             if (out == null) {
265                 return;
266             }
267             try (Writer w = out) {
268                 flushBuffer();
269             } finally {
270                 out = null;
271                 cb = null;
272             }
273         }
274     }
275 }
276