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GZIPOutputStream.java
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1998-09-22
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/*
* @(#)GZIPOutputStream.java 1.11 97/01/24
*
* Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
*
* This software is the confidential and proprietary information of Sun
* Microsystems, Inc. ("Confidential Information"). You shall not
* disclose such Confidential Information and shall use it only in
* accordance with the terms of the license agreement you entered into
* with Sun.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
* IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
* PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
* SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
* THIS SOFTWARE OR ITS DERIVATIVES.
*
* CopyrightVersion 1.1_beta
*
*/
package java.util.zip;
import java.io.OutputStream;
import java.io.IOException;
/**
* This class implements a stream filter for writing compressed data in
* the GZIP file format.
* @version 1.11, 01/24/97
* @author David Connelly
*
*/
public
class GZIPOutputStream extends DeflaterOutputStream {
/**
* CRC-32 of uncompressed data.
*/
protected CRC32 crc = new CRC32();
/*
* GZIP header magic number.
*/
private final static int GZIP_MAGIC = 0x8b1f;
/**
* Creates a new output stream with the specified buffer size.
* @param out the output stream
* @param size the output buffer size
* @exception IOException If an I/O error has occurred.
*/
public GZIPOutputStream(OutputStream out, int size) throws IOException {
super(out, new Deflater(Deflater.DEFAULT_COMPRESSION, true), size);
writeHeader();
crc.reset();
}
/**
* Creates a new output stream with a default buffer size.
* @param out the output stream
* @exception IOException If an I/O error has occurred.
*/
public GZIPOutputStream(OutputStream out) throws IOException {
this(out, 512);
}
/**
* Writes array of bytes to the compressed output stream. This method
* will block until all the bytes are written.
* @param buf the data to be written
* @param off the start offset of the data
* @param len the length of the data
* @exception IOException If an I/O error has occurred.
*/
public synchronized void write(byte[] buf, int off, int len)
throws IOException
{
super.write(buf, off, len);
crc.update(buf, off, len);
}
/**
* Finishes writing compressed data to the output stream without closing
* the underlying stream. Use this method when applying multiple filters
* in succession to the same output stream.
* @exception IOException if an I/O error has occurred
*/
public void finish() throws IOException {
if (!def.finished()) {
def.finish();
while (!def.finished()) {
deflate();
}
writeTrailer();
}
}
/**
* Writes remaining compressed data to the output stream and closes the
* underlying stream.
* @exception IOException if an I/O error has occurred
*/
public void close() throws IOException {
finish();
out.close();
}
/*
* Writes GZIP member header.
*/
private void writeHeader() throws IOException {
writeShort(GZIP_MAGIC); // Magic number
out.write(def.DEFLATED); // Compression method (CM)
out.write(0); // Flags (FLG)
writeInt(0); // Modification time (MTIME)
out.write(0); // Extra flags (XFL)
out.write(0); // Operating system (OS)
}
/*
* Writes GZIP member trailer.
*/
private void writeTrailer() throws IOException {
writeInt((int)crc.getValue()); // CRC-32 of uncompressed data
writeInt(def.getTotalIn()); // Number of uncompressed bytes
}
/*
* Writes integer in Intel byte order.
*/
private void writeInt(int i) throws IOException {
writeShort(i & 0xffff);
writeShort((i >> 16) & 0xffff);
}
/*
* Writes short integer in Intel byte order.
*/
private void writeShort(int s) throws IOException {
out.write(s & 0xff);
out.write((s >> 8) & 0xff);
}
}