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BufferedOutputStream.java
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BufferedOutputStream.java
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/*
* Copyright (c) 1994, 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.io;
import java.util.Arrays;
import jdk.internal.misc.InternalLock;
import jdk.internal.misc.VM;
/**
* The class implements a buffered output stream. By setting up such
* an output stream, an application can write bytes to the underlying
* output stream without necessarily causing a call to the underlying
* system for each byte written.
*
* @author Arthur van Hoff
* @since 1.0
*/
public class BufferedOutputStream extends FilterOutputStream {
private static final int DEFAULT_INITIAL_BUFFER_SIZE = 512;
private static final int DEFAULT_MAX_BUFFER_SIZE = 8192;
// initialized to null when BufferedOutputStream is sub-classed
private final InternalLock lock;
/**
* The internal buffer where data is stored.
*/
protected byte[] buf;
/**
* The number of valid bytes in the buffer. This value is always
* in the range {@code 0} through {@code buf.length}; elements
* {@code buf[0]} through {@code buf[count-1]} contain valid
* byte data.
*/
protected int count;
/**
* Max size of the internal buffer.
*/
private final int maxBufSize;
/**
* Returns the buffer size to use when no output buffer size specified.
*/
private static int initialBufferSize() {
if (VM.isBooted() && Thread.currentThread().isVirtual()) {
return DEFAULT_INITIAL_BUFFER_SIZE;
} else {
return DEFAULT_MAX_BUFFER_SIZE;
}
}
/**
* Creates a new buffered output stream.
*/
private BufferedOutputStream(OutputStream out, int initialSize, int maxSize) {
super(out);
if (initialSize <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
if (getClass() == BufferedOutputStream.class) {
// use InternalLock and resizable buffer when not sub-classed
this.lock = InternalLock.newLockOrNull();
this.buf = new byte[initialSize]; // resizable
} else {
// use monitors and no resizing when sub-classed
this.lock = null;
this.buf = new byte[maxSize];
}
this.maxBufSize = maxSize;
}
/**
* Creates a new buffered output stream to write data to the
* specified underlying output stream.
*
* @param out the underlying output stream.
*/
public BufferedOutputStream(OutputStream out) {
this(out, initialBufferSize(), DEFAULT_MAX_BUFFER_SIZE);
}
/**
* Creates a new buffered output stream to write data to the
* specified underlying output stream with the specified buffer
* size.
*
* @param out the underlying output stream.
* @param size the buffer size.
* @throws IllegalArgumentException if size <= 0.
*/
public BufferedOutputStream(OutputStream out, int size) {
this(out, size, size);
}
/** Flush the internal buffer */
private void flushBuffer() throws IOException {
if (count > 0) {
out.write(buf, 0, count);
count = 0;
}
}
/**
* Grow buf to fit an additional len bytes if needed.
* If possible, it grows by len+1 to avoid flushing when len bytes
* are added. A no-op if the buffer is not resizable.
*
* This method should only be called while holding the lock.
*/
private void growIfNeeded(int len) {
int neededSize = count + len + 1;
if (neededSize < 0)
neededSize = Integer.MAX_VALUE;
int bufSize = buf.length;
if (neededSize > bufSize && bufSize < maxBufSize) {
int newSize = Math.min(neededSize, maxBufSize);
buf = Arrays.copyOf(buf, newSize);
}
}
/**
* Writes the specified byte to this buffered output stream.
*
* @param b the byte to be written.
* @throws IOException if an I/O error occurs.
*/
@Override
public void write(int b) throws IOException {
if (lock != null) {
lock.lock();
try {
implWrite(b);
} finally {
lock.unlock();
}
} else {
synchronized (this) {
implWrite(b);
}
}
}
private void implWrite(int b) throws IOException {
growIfNeeded(1);
if (count >= buf.length) {
flushBuffer();
}
buf[count++] = (byte)b;
}
/**
* Writes {@code len} bytes from the specified byte array
* starting at offset {@code off} to this buffered output stream.
*
* <p> Ordinarily this method stores bytes from the given array into this
* stream's buffer, flushing the buffer to the underlying output stream as
* needed. If the requested length is at least as large as this stream's
* buffer, however, then this method will flush the buffer and write the
* bytes directly to the underlying output stream. Thus redundant
* {@code BufferedOutputStream}s will not copy data unnecessarily.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @throws IOException if an I/O error occurs.
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public void write(byte[] b, int off, int len) throws IOException {
if (lock != null) {
lock.lock();
try {
implWrite(b, off, len);
} finally {
lock.unlock();
}
} else {
synchronized (this) {
implWrite(b, off, len);
}
}
}
private void implWrite(byte[] b, int off, int len) throws IOException {
if (len >= maxBufSize) {
/* If the request length exceeds the max size of the output buffer,
flush the output buffer and then write the data directly.
In this way buffered streams will cascade harmlessly. */
flushBuffer();
out.write(b, off, len);
return;
}
growIfNeeded(len);
if (len > buf.length - count) {
flushBuffer();
}
System.arraycopy(b, off, buf, count, len);
count += len;
}
/**
* Flushes this buffered output stream. This forces any buffered
* output bytes to be written out to the underlying output stream.
*
* @throws IOException if an I/O error occurs.
* @see java.io.FilterOutputStream#out
*/
@Override
public void flush() throws IOException {
if (lock != null) {
lock.lock();
try {
implFlush();
} finally {
lock.unlock();
}
} else {
synchronized (this) {
implFlush();
}
}
}
private void implFlush() throws IOException {
flushBuffer();
out.flush();
}
}