Java压缩技术（六） BZIP2——Commons实现
想要把一整套算法都整理出来，的确是件非常老心费力的事情！http://www.agoit.com/images/smiles/icon_sad.gif 但是如果一件事情不能有始有终，难免会有遗憾！http://www.agoit.com/images/smiles/icon_smile.gif 索性，继续整理！http://www.agoit.com/images/smiles/icon_biggrin.gif相关链接：
Java压缩技术（一） ZLib
Java压缩技术（二） ZIP压缩——Java原生实现
Java压缩技术（三） ZIP解压缩——Java原生实现
Java压缩技术（四） GZIP——Java原生实现
Java压缩技术（五） GZIP相关——浏览器解析
Java压缩技术（六） BZIP2——Commons实现
Java压缩技术（七） TAR——Commons实现
BZip2与GZip有什么渊源，我这里不深究。我要说的只是，这两种算法，你在linux下都可以找到相应的操作命令。
GZip
压缩
gzip <file> 将得到压缩文件<file>.gz，同时删除文件<file>
解压缩
gzip -d <file>.gz 将得到压缩文件<file>，同时删除文件<file>.gz
BZip2与之相当，几乎没有什么差别～～
BZip2
压缩
bzip2 <file> 将得到压缩文件<file>.bz2，同时删除文件<file>
解压缩
bzip2 -d <file>.bz2 将得到压缩文件<file>，同时删除文件<file>.bz2
除了命令不同外，几乎是一样的！http://www.agoit.com/images/smiles/icon_biggrin.gif
再说实现。GZIP是JDK自带的算法实现，但BZip2则不曾享受这个待遇。http://www.agoit.com/images/smiles/icon_sad.gif 不过，强大的Apache坚决不会让这些个在Linux下如鱼得水的算法在Java世界中销声匿迹。Apache在Commons Compress中提供了相应的实现。同时，还包括众所周知的tar、cpio、zip等算法实现，其中最为丰富的当属zip实现了！http://www.agoit.com/images/smiles/icon_biggrin.gif
我继续依葫芦画瓢～～～
BZip2CompressorOutputStream类用于压缩
BZip2CompressorInputStream类用于解压缩
先说压缩实现，BZip2CompressorOutputStream只有一个方法用于压缩，就是带定长的write方法。简单调用如下文所示：
/** * 数据压缩 ** @param is * @param os * @throws Exception */public static void compress(InputStream is, OutputStream os)throws Exception {BZip2CompressorOutputStream gos = new BZip2CompressorOutputStream(os);int count;byte data[] = new byte;while ((count = is.read(data, 0, BUFFER)) != -1) {gos.write(data, 0, count);}gos.finish();gos.flush();gos.close();}
与GZip实现有何差别？除了换掉了GZIPOutputStream没有任何差别。http://www.agoit.com/images/smiles/icon_smile.gif
解压缩就更不用说了，BZip2CompressorInputStream提供了一个带定长的read方法。简单调用如下文所示：
/** * 数据解压缩 ** @param is * @param os * @throws Exception */public static void decompress(InputStream is, OutputStream os)throws Exception {BZip2CompressorInputStream gis = new BZip2CompressorInputStream(is);int count;byte data[] = new byte;while ((count = gis.read(data, 0, BUFFER)) != -1) {os.write(data, 0, count);}gis.close();}
嗯，没什么难度！http://www.agoit.com/images/smiles/icon_biggrin.gif
IT这行就是这样，只要你肯用心，能触类旁通，就能融会贯通！http://www.agoit.com/images/smiles/icon_biggrin.gif
给一个完整实现：
/** * 2010-4-15 */package org.zlex.commons.compress.compress;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.InputStream;import java.io.OutputStream;import org.apache.commons.compress.compressors.bzip2.BZip2CompressorInputStream;import org.apache.commons.compress.compressors.bzip2.BZip2CompressorOutputStream;/** * BZip2工具 ** @author<a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @since 1.0 */public abstract class BZip2Utils {public static final int BUFFER = 1024;public static final CharSequence EXT = ".bz2";/** * 数据压缩 ** @param data * @return * @throws Exception */public static byte[] compress(byte[] data) throws Exception {ByteArrayInputStream bais = new ByteArrayInputStream(data);ByteArrayOutputStream baos = new ByteArrayOutputStream();// 压缩compress(bais, baos);byte[] output = baos.toByteArray();baos.flush();baos.close();bais.close();return output;}/** * 文件压缩 ** @param file * @throws Exception */public static void compress(File file) throws Exception {compress(file, true);}/** * 文件压缩 ** @param file * @param delete * 是否删除原始文件 * @throws Exception */public static void compress(File file, boolean delete) throws Exception {FileInputStream fis = new FileInputStream(file);FileOutputStream fos = new FileOutputStream(file.getPath() + EXT);compress(fis, fos);fis.close();fos.flush();fos.close();if (delete) {file.delete();}}/** * 数据压缩 ** @param is * @param os * @throws Exception */public static void compress(InputStream is, OutputStream os)throws Exception {BZip2CompressorOutputStream gos = new BZip2CompressorOutputStream(os);int count;byte data[] = new byte;while ((count = is.read(data, 0, BUFFER)) != -1) {gos.write(data, 0, count);}gos.finish();gos.flush();gos.close();}/** * 文件压缩 ** @param path * @throws Exception */public static void compress(String path) throws Exception {compress(path, true);}/** * 文件压缩 ** @param path * @param delete * 是否删除原始文件 * @throws Exception */public static void compress(String path, boolean delete) throws Exception {File file = new File(path);compress(file, delete);}/** * 数据解压缩 ** @param data * @return * @throws Exception */public static byte[] decompress(byte[] data) throws Exception {ByteArrayInputStream bais = new ByteArrayInputStream(data);ByteArrayOutputStream baos = new ByteArrayOutputStream();// 解压缩decompress(bais, baos);data = baos.toByteArray();baos.flush();baos.close();bais.close();return data;}/** * 文件解压缩 ** @param file * @throws Exception */public static void decompress(File file) throws Exception {decompress(file, true);}/** * 文件解压缩 ** @param file * @param delete * 是否删除原始文件 * @throws Exception */public static void decompress(File file, boolean delete) throws Exception {FileInputStream fis = new FileInputStream(file);FileOutputStream fos = new FileOutputStream(file.getPath().replace(EXT,""));decompress(fis, fos);fis.close();fos.flush();fos.close();if (delete) {file.delete();}}/** * 数据解压缩 ** @param is * @param os * @throws Exception */public static void decompress(InputStream is, OutputStream os)throws Exception {BZip2CompressorInputStream gis = new BZip2CompressorInputStream(is);int count;byte data[] = new byte;while ((count = gis.read(data, 0, BUFFER)) != -1) {os.write(data, 0, count);}gis.close();}/** * 文件解压缩 ** @param path * @throws Exception */public static void decompress(String path) throws Exception {decompress(path, true);}/** * 文件解压缩 ** @param path * @param delete * 是否删除原始文件 * @throws Exception */public static void decompress(String path, boolean delete) throws Exception {File file = new File(path);decompress(file, delete);}}
对应再来个测试用例，测试用例如下所示：
/** * 2010-4-13 */package org.zlex.commons.compress.compress;import static org.junit.Assert.assertEquals;import java.io.DataInputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import org.junit.Test;/** * BZip2 ** @author <a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @since 1.0 */public class BZip2UtilsTest {private String inputStr = "zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org,zlex@zlex.org,snowolf@zlex.org,zlex.snowolf@zlex.org";@Testpublic final void testDataCompress() throws Exception {byte[] input = inputStr.getBytes();System.err.println("原文:\t" + inputStr);System.err.println("长度:\t" + input.length);byte[] data = BZip2Utils.compress(input);System.err.println("压缩后:\t");System.err.println("长度:\t" + data.length);byte[] output = BZip2Utils.decompress(data);String outputStr = new String(output);System.err.println("解压缩后:\t" + outputStr);System.err.println("长度:\t" + output.length);assertEquals(inputStr, outputStr);}@Testpublic final void testFileCompress() throws Exception {FileOutputStream fos = new FileOutputStream("d:/f.txt");fos.write(inputStr.getBytes());fos.flush();fos.close();BZip2Utils.compress("d:/f.txt");BZip2Utils.decompress("d:/f.txt.bz2");File file = new File("d:/f.txt");FileInputStream fis = new FileInputStream(file);DataInputStream dis = new DataInputStream(fis);byte[] data = new byte[(int) file.length()];dis.readFully(data);fis.close();String outputStr = new String(data);assertEquals(inputStr, outputStr);}}
虽然，两种算法在代码实现上几乎没有什么差别，但在压缩上想要看到效果，还真让我费了点事！http://www.agoit.com/images/smiles/icon_smile.gif
控制台输出如下所示：
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