cd /home/xm/compress   進入compress目錄
touch HadoopImg.java  建立java檔案
vim HadoopImg.java  寫進程式碼 （附後）

對.java檔案進行編譯
javac HadoopImg.java 得到class檔案

打jar包
jar -cvf hadoopimgc.jar HadoopImg.class

進行壓縮

[root@master compress]# $HADOOP_HOME/bin/hadoop jar ./hadoopimgc.jar compress timg BZip2Codec

hadoopimgc.jar 為要執行的jar包
compress jar包中要執行的函式
timg 要壓縮的檔案
BZip2Codec 採取的壓縮方法

解壓縮

[root@master compress]# $HADOOP_HOME/bin/hadoop jar ./hadoopimgc.jar decompress timg.bz2

decompress 執行的函式
timg.bz2 解壓縮的檔案

java原始碼：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundExceiption;
import java.io.FileOutputStream;
import java.io.IOException
 
;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Date;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory
 
;
import org.apache.hadoop.io.compress.CompressionOutputStream;
import org.apache.hadoop.util.ReflectionUtils;


public class HadoopImg {
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        if (args[0].equals("compress")) {
            compress(args[1], "org.apache.hadoop.io.compress." + args[2]);
        }       
        else if (args[0].equals("decompress"))
            decompres(args[1]);
        else {
            System.err.println("Error!\n usgae: hadoop jar HadoopImg.jar [compress] [filename] [compress type]");
            System.err.println("\t\ror [decompress] [filename] ");
            return;
        }
        System.out.println("down");
    }

    /*
     * filename是希望壓縮的原始檔案,method是欲使用的壓縮方法（如BZip2Codec等）
     */
    public static void compress(String filername, String method) throws ClassNotFoundException, IOException {
        System.out.println("[" + new Date() + "] : enter compress");
        File fileIn = new File(filername);
        InputStream in = new FileInputStream(fileIn);

        Class codecClass = Class.forName(method);       
        Configuration conf = new Configuration();   

        // 通過名稱找到對應的編碼/解碼器
        CompressionCodec codec = (CompressionCodec)
                ReflectionUtils.newInstance(codecClass, conf);

        // 該壓縮方法對應的副檔名
        File fileOut = new File(filername + codec.getDefaultExtension()); 
        fileOut.delete();

        OutputStream out = new FileOutputStream(fileOut);
        CompressionOutputStream cout = codec.createOutputStream(out);

        System.out.println("[" + new Date() + "]: start compressing ");
        IOUtils.copyBytes(in, cout, 1024*1024*5, false);        // 緩衝區設為5MB
        System.out.println("[" + new Date() + "]: compressing finished ");

        in.close();
        cout.close();
    }

    /*
     * filename是希望解壓的檔案
     */
    public static void decompres(String filename) throws FileNotFoundException, IOException {
        System.out.println("[" + new Date() + "] : enter compress");

        Configuration conf = new Configuration();
        CompressionCodecFactory factory = new CompressionCodecFactory(conf);        
        CompressionCodec codec = factory.getCodec(new Path(filename));
        if (null == codec) {
            System.out.println("Cannot find codec for file " + filename);
            return;
        }

        File fout = new File(filename+ ".decoded");
        InputStream cin = codec.createInputStream(new FileInputStream(filename));
        OutputStream out = new FileOutputStream(fout);

        System.out.println("[" + new Date() + "]: start decompressing ");
        IOUtils.copyBytes(cin, out, 1024*1024*5, false);
        System.out.println("[" + new Date() + "]: decompressing finished ");

        cin.close();
        out.close();
    }
}