下面是一個使用gzip工具壓縮檔案的例子。將檔案/user/hadoop/aa.txt進行壓縮，壓縮後為/user/hadoop/text.gz

package com.hdfs;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
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.CompressionInputStream;
import org.apache.hadoop.io.compress.CompressionOutputStream;
import org.apache.hadoop.util.ReflectionUtils;

public class CodecTest {
    //壓縮檔案
    public static void compress(String codecClassName) throws Exception{
        Class<?> codecClass = Class.forName(codecClassName);
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(conf);
        CompressionCodec codec = (CompressionCodec)ReflectionUtils.newInstance(codecClass, conf);
        //指定壓縮檔案路徑
        FSDataOutputStream outputStream = fs.create(new Path("/user/hadoop/text.gz"));
        //指定要被壓縮的檔案路徑
        FSDataInputStream in = fs.open(new Path("/user/hadoop/aa.txt"));
        //建立壓縮輸出流
        CompressionOutputStream out = codec.createOutputStream(outputStream);  
        IOUtils.copyBytes(in, out, conf); 
        IOUtils.closeStream(in);
        IOUtils.closeStream(out);
    }
    
    //解壓縮
    public static void uncompress(String fileName) throws Exception{
        Class<?> codecClass = Class.forName("org.apache.hadoop.io.compress.GzipCodec");
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(conf);
        CompressionCodec codec = (CompressionCodec)ReflectionUtils.newInstance(codecClass, conf);
        FSDataInputStream inputStream = fs.open(new Path("/user/hadoop/text.gz"));
         //把text檔案裡到資料解壓，然後輸出到控制檯  
        InputStream in = codec.createInputStream(inputStream);  
        IOUtils.copyBytes(in, System.out, conf);
        IOUtils.closeStream(in);
    }
    
    //使用副檔名來推斷二來的codec來對檔案進行解壓縮
    public static void uncompress1(String uri) throws IOException{
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(uri), conf);
        
        Path inputPath = new Path(uri);
        CompressionCodecFactory factory = new CompressionCodecFactory(conf);
        CompressionCodec codec = factory.getCodec(inputPath);
        if(codec == null){
            System.out.println("no codec found for " + uri);
            System.exit(1);
        }
        String outputUri = CompressionCodecFactory.removeSuffix(uri, codec.getDefaultExtension());
        InputStream in = null;
        OutputStream out = null;
        try {
            in = codec.createInputStream(fs.open(inputPath));
            out = fs.create(new Path(outputUri));
            IOUtils.copyBytes(in, out, conf);
        } finally{
            IOUtils.closeStream(out);
            IOUtils.closeStream(in);
        }
    }
    
    public static void main(String[] args) throws Exception {
        //compress("org.apache.hadoop.io.compress.GzipCodec");
        //uncompress("text");
        uncompress1("hdfs://master:9000/user/hadoop/text.gz");
    }

}
 

首先執行77行進行壓縮，壓縮後執行第78行進行解壓縮，這裡解壓到標準輸出，所以執行78行會再控制檯看到檔案/user/hadoop/aa.txt的內容。如果執行79行的話會將檔案解壓到/user/hadoop/text,他是根據/user/hadoop/text.gz的副檔名判斷使用哪個解壓工具進行解壓的。解壓後的路徑就是去掉副檔名。

　　進行檔案壓縮後，在執行命令./hadoop fs -ls /user/hadoop/檢視檔案資訊，如下：

1 [[email protected] bin]$ ./hadoop fs -ls /user/hadoop/
2 Found 7 items
3 -rw-r--r--   3 hadoop supergroup   76805248 2013-06-17 23:55 /user/hadoop/aa.mp4
 
4 -rw-r--r--   3 hadoop supergroup        520 2013-06-17 22:29 /user/hadoop/aa.txt
5 drwxr-xr-x   - hadoop supergroup          0 2013-06-16 17:19 /user/hadoop/input
6 drwxr-xr-x   - hadoop supergroup          0 2013-06-16 19:32 /user/hadoop/output
7 drwxr-xr-x   - hadoop supergroup          0 2013-06-18 17:08 /user/hadoop/test
 
8 drwxr-xr-x   - hadoop supergroup          0 2013-06-18 19:45 /user/hadoop/test1
9 -rw-r--r--   3 hadoop supergroup         46 2013-06-19 20:09 /user/hadoop/text.gz

第4行為壓縮之前的檔案，大小為520個位元組。第9行為壓縮後的檔案，大小為46個位元組。由此可以看出上面講的壓縮的兩大好處了。