Java压缩技术（六） BZIP2——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！  

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。  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！  

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[BUFFER];
     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。  

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[BUFFER];
     while ((count = gis.read(data, 0, BUFFER)) != -1) {
         os.write(data, 0, count);
     }

     gis.close();
 }

嗯，没什么难度！  
IT这行就是这样，只要你肯用心，能触类旁通，就能融会贯通！  
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:[email protected]">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[BUFFER];
         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[BUFFER];
         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:[email protected]">梁栋</a>
  * @since 1.0
  */
 public class BZip2UtilsTest {

     private String inputStr = "[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]";

     @Test
     public 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);

     }

     @Test
     public 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！  
控制台输出如下所示： 

引用

原文: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]
长度: 529 
压缩后:
长度: 76 
解压缩后: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]
长度: 529 

529字节-->76字节！ 
GZIP本身不需要太长的内容，经过压缩就能体现出压缩效果，而BZip2则需要压缩很长的内容时，才能体现其压缩效果，这说明BZip2更适合大数据压缩？！  

Commons Compress不仅支持BZip2算法实现，同时也支持GZip算法实现。对于GZip算法实现，与Java原生实现基本上没有什么差别。其源代码分析，仅仅是做了简单的包装。 
不过有必要提及的一点是，Commons Compress为压缩（GZip和BZip2）构建了压缩算法工厂类 CompressorStreamFactory 。通过这个类可以方便的构建GZip和BZip2的输入输出流，关键字分别为“gz”和“bzip2”。 
GZip 

 // GzipCompressorInputStream
 CompressorInputStream gzipIn = new CompressorStreamFactory()
         .createCompressorInputStream("gz", is);

 // GzipCompressorOutputStream
 CompressorOutputStream gzipOut = new CompressorStreamFactory()
         .createCompressorOutputStream("gz", os);

BZip2 

 // BZip2CompressorInputStream
 CompressorInputStream bzip2In = new CompressorStreamFactory()
         .createCompressorInputStream("bzip2", is);

 // BZip2CompressorOutputStream
 CompressorOutputStream bzip2Out = new CompressorStreamFactory()
         .createCompressorOutputStream("bzip2", os);

GZip和BZip2在算法实现步骤上基本上没有什么差别，如果有必要统一，可按上述代码实现！