1， BufferedWriter 提高效率就是因为把数据写入了缓冲区 下面是源码 你可以看看。
2，如果要是文件很大的话，应该需要拆分处理。http://www.oschina.net/code/snippet_54100_7938
3. BufferOutputStream 也是因为缓冲区才提高效率 具体也得看源码
/*
* @(#)BufferedWriter.java 1.29 05/11/30
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.io;
/**
* Writes text to a character-output stream, buffering characters so as to
* provide for the efficient writing of single characters, arrays, and strings.
*
* <p> The buffer size may be specified, or the default size may be accepted.
* The default is large enough for most purposes.
*
* <p> A newLine() method is provided, which uses the platform's own notion of
* line separator as defined by the system property <tt>line.separator</tt>.
* 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.
*
* <p> 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,
*
* <pre>
* PrintWriter out
* = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
* </pre>
*
* 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
*
* @version 1.29, 05/11/30
* @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 = (String) 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.
*
* <p> 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
* <code>BufferedWriter</code>s 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.
*
* <p> If the value of the <tt>len</tt> 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 <tt>line.separator</tt>, 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;
}
}
}
}
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