gzipoutputstream.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 145 行

/*
 * @(#)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);
    }
}