The buffer size may be specified, or the default size may be accepted. + * The default is large enough for most purposes. + * + *
A newLine() method is provided, which uses the platform's own notion of + * line separator as defined by the system property line.separator. + * Not all platforms use the newline character ('\n') to terminate lines. + * Calling this method to terminate each output line is therefore preferred to + * writing a newline character directly. + * + *
In general, a Writer sends its output immediately to the underlying + * character or byte stream. Unless prompt output is required, it is advisable + * to wrap a BufferedWriter around any Writer whose write() operations may be + * costly, such as FileWriters and OutputStreamWriters. For example, + * + *
+ * PrintWriter out
+ * = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
+ *
+ *
+ * will buffer the PrintWriter's output to the file. Without buffering, each
+ * invocation of a print() method would cause characters to be converted into
+ * bytes that would then be written immediately to the file, which can be very
+ * inefficient.
+ *
+ * @see PrintWriter
+ * @see FileWriter
+ * @see OutputStreamWriter
+ * @see java.nio.file.Files#newBufferedWriter
+ *
+ * @author Mark Reinhold
+ * @since JDK1.1
+ */
+
+public class BufferedWriter extends Writer {
+
+ private Writer out;
+
+ private char cb[];
+ private int nChars, nextChar;
+
+ private static int defaultCharBufferSize = 8192;
+
+ /**
+ * Line separator string. This is the value of the line.separator
+ * property at the moment that the stream was created.
+ */
+ private String lineSeparator;
+
+ /**
+ * Creates a buffered character-output stream that uses a default-sized
+ * output buffer.
+ *
+ * @param out A Writer
+ */
+ public BufferedWriter(Writer out) {
+ this(out, defaultCharBufferSize);
+ }
+
+ /**
+ * Creates a new buffered character-output stream that uses an output
+ * buffer of the given size.
+ *
+ * @param out A Writer
+ * @param sz Output-buffer size, a positive integer
+ *
+ * @exception IllegalArgumentException If sz is <= 0
+ */
+ public BufferedWriter(Writer out, int sz) {
+ super(out);
+ if (sz <= 0)
+ throw new IllegalArgumentException("Buffer size <= 0");
+ this.out = out;
+ cb = new char[sz];
+ nChars = sz;
+ nextChar = 0;
+
+ lineSeparator = java.security.AccessController.doPrivileged(
+ new sun.security.action.GetPropertyAction("line.separator"));
+ }
+
+ /** Checks to make sure that the stream has not been closed */
+ private void ensureOpen() throws IOException {
+ if (out == null)
+ throw new IOException("Stream closed");
+ }
+
+ /**
+ * Flushes the output buffer to the underlying character stream, without
+ * flushing the stream itself. This method is non-private only so that it
+ * may be invoked by PrintStream.
+ */
+ void flushBuffer() throws IOException {
+ synchronized (lock) {
+ ensureOpen();
+ if (nextChar == 0)
+ return;
+ out.write(cb, 0, nextChar);
+ nextChar = 0;
+ }
+ }
+
+ /**
+ * Writes a single character.
+ *
+ * @exception IOException If an I/O error occurs
+ */
+ public void write(int c) throws IOException {
+ synchronized (lock) {
+ ensureOpen();
+ if (nextChar >= nChars)
+ flushBuffer();
+ cb[nextChar++] = (char) c;
+ }
+ }
+
+ /**
+ * Our own little min method, to avoid loading java.lang.Math if we've run
+ * out of file descriptors and we're trying to print a stack trace.
+ */
+ private int min(int a, int b) {
+ if (a < b) return a;
+ return b;
+ }
+
+ /**
+ * Writes a portion of an array of characters.
+ *
+ * Ordinarily this method stores characters from the given array into
+ * this stream's buffer, flushing the buffer to the underlying stream as
+ * needed. If the requested length is at least as large as the buffer,
+ * however, then this method will flush the buffer and write the characters
+ * directly to the underlying stream. Thus redundant
+ * BufferedWriters will not copy data unnecessarily.
+ *
+ * @param cbuf A character array
+ * @param off Offset from which to start reading characters
+ * @param len Number of characters to write
+ *
+ * @exception IOException If an I/O error occurs
+ */
+ public void write(char cbuf[], int off, int len) throws IOException {
+ synchronized (lock) {
+ ensureOpen();
+ if ((off < 0) || (off > cbuf.length) || (len < 0) ||
+ ((off + len) > cbuf.length) || ((off + len) < 0)) {
+ throw new IndexOutOfBoundsException();
+ } else if (len == 0) {
+ return;
+ }
+
+ if (len >= nChars) {
+ /* If the request length exceeds the size of the output buffer,
+ flush the buffer and then write the data directly. In this
+ way buffered streams will cascade harmlessly. */
+ flushBuffer();
+ out.write(cbuf, off, len);
+ return;
+ }
+
+ int b = off, t = off + len;
+ while (b < t) {
+ int d = min(nChars - nextChar, t - b);
+ System.arraycopy(cbuf, b, cb, nextChar, d);
+ b += d;
+ nextChar += d;
+ if (nextChar >= nChars)
+ flushBuffer();
+ }
+ }
+ }
+
+ /**
+ * Writes a portion of a String.
+ *
+ *
If the value of the len parameter is negative then no + * characters are written. This is contrary to the specification of this + * method in the {@linkplain java.io.Writer#write(java.lang.String,int,int) + * superclass}, which requires that an {@link IndexOutOfBoundsException} be + * thrown. + * + * @param s String to be written + * @param off Offset from which to start reading characters + * @param len Number of characters to be written + * + * @exception IOException If an I/O error occurs + */ + public void write(String s, int off, int len) throws IOException { + synchronized (lock) { + ensureOpen(); + + int b = off, t = off + len; + while (b < t) { + int d = min(nChars - nextChar, t - b); + s.getChars(b, b + d, cb, nextChar); + b += d; + nextChar += d; + if (nextChar >= nChars) + flushBuffer(); + } + } + } + + /** + * Writes a line separator. The line separator string is defined by the + * system property line.separator, and is not necessarily a single + * newline ('\n') character. + * + * @exception IOException If an I/O error occurs + */ + public void newLine() throws IOException { + write(lineSeparator); + } + + /** + * Flushes the stream. + * + * @exception IOException If an I/O error occurs + */ + public void flush() throws IOException { + synchronized (lock) { + flushBuffer(); + out.flush(); + } + } + + public void close() throws IOException { + synchronized (lock) { + if (out == null) { + return; + } + try { + flushBuffer(); + } finally { + out.close(); + out = null; + cb = null; + } + } + } +}