001 /*
002 * Copyright 1996-2002 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.util.zip;
027
028 import java.io.OutputStream;
029 import java.io.IOException;
030
031 /**
032 * This class implements a stream filter for writing compressed data in
033 * the GZIP file format.
034 * @version 1.29, 05/05/07
035 * @author David Connelly
036 *
037 */
038 public class GZIPOutputStream extends DeflaterOutputStream {
039 /**
040 * CRC-32 of uncompressed data.
041 */
042 protected CRC32 crc = new CRC32();
043
044 /*
045 * GZIP header magic number.
046 */
047 private final static int GZIP_MAGIC = 0x8b1f;
048
049 /*
050 * Trailer size in bytes.
051 *
052 */
053 private final static int TRAILER_SIZE = 8;
054
055 /**
056 * Creates a new output stream with the specified buffer size.
057 * @param out the output stream
058 * @param size the output buffer size
059 * @exception IOException If an I/O error has occurred.
060 * @exception IllegalArgumentException if size is <= 0
061 */
062 public GZIPOutputStream(OutputStream out, int size)
063 throws IOException {
064 super (out, new Deflater(Deflater.DEFAULT_COMPRESSION, true),
065 size);
066 usesDefaultDeflater = true;
067 writeHeader();
068 crc.reset();
069 }
070
071 /**
072 * Creates a new output stream with a default buffer size.
073 * @param out the output stream
074 * @exception IOException If an I/O error has occurred.
075 */
076 public GZIPOutputStream(OutputStream out) throws IOException {
077 this (out, 512);
078 }
079
080 /**
081 * Writes array of bytes to the compressed output stream. This method
082 * will block until all the bytes are written.
083 * @param buf the data to be written
084 * @param off the start offset of the data
085 * @param len the length of the data
086 * @exception IOException If an I/O error has occurred.
087 */
088 public synchronized void write(byte[] buf, int off, int len)
089 throws IOException {
090 super .write(buf, off, len);
091 crc.update(buf, off, len);
092 }
093
094 /**
095 * Finishes writing compressed data to the output stream without closing
096 * the underlying stream. Use this method when applying multiple filters
097 * in succession to the same output stream.
098 * @exception IOException if an I/O error has occurred
099 */
100 public void finish() throws IOException {
101 if (!def.finished()) {
102 def.finish();
103 while (!def.finished()) {
104 int len = def.deflate(buf, 0, buf.length);
105 if (def.finished() && len <= buf.length - TRAILER_SIZE) {
106 // last deflater buffer. Fit trailer at the end
107 writeTrailer(buf, len);
108 len = len + TRAILER_SIZE;
109 out.write(buf, 0, len);
110 return;
111 }
112 if (len > 0)
113 out.write(buf, 0, len);
114 }
115 // if we can't fit the trailer at the end of the last
116 // deflater buffer, we write it separately
117 byte[] trailer = new byte[TRAILER_SIZE];
118 writeTrailer(trailer, 0);
119 out.write(trailer);
120 }
121 }
122
123 /*
124 * Writes GZIP member header.
125 */
126
127 private final static byte[] header = { (byte) GZIP_MAGIC, // Magic number (short)
128 (byte) (GZIP_MAGIC >> 8), // Magic number (short)
129 Deflater.DEFLATED, // Compression method (CM)
130 0, // Flags (FLG)
131 0, // Modification time MTIME (int)
132 0, // Modification time MTIME (int)
133 0, // Modification time MTIME (int)
134 0, // Modification time MTIME (int)
135 0, // Extra flags (XFLG)
136 0 // Operating system (OS)
137 };
138
139 private void writeHeader() throws IOException {
140 out.write(header);
141 }
142
143 /*
144 * Writes GZIP member trailer to a byte array, starting at a given
145 * offset.
146 */
147 private void writeTrailer(byte[] buf, int offset)
148 throws IOException {
149 writeInt((int) crc.getValue(), buf, offset); // CRC-32 of uncompr. data
150 writeInt(def.getTotalIn(), buf, offset + 4); // Number of uncompr. bytes
151 }
152
153 /*
154 * Writes integer in Intel byte order to a byte array, starting at a
155 * given offset.
156 */
157 private void writeInt(int i, byte[] buf, int offset)
158 throws IOException {
159 writeShort(i & 0xffff, buf, offset);
160 writeShort((i >> 16) & 0xffff, buf, offset + 2);
161 }
162
163 /*
164 * Writes short integer in Intel byte order to a byte array, starting
165 * at a given offset
166 */
167 private void writeShort(int s, byte[] buf, int offset)
168 throws IOException {
169 buf[offset] = (byte) (s & 0xff);
170 buf[offset + 1] = (byte) ((s >> 8) & 0xff);
171 }
172 }
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