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package cn.edu.xmu.dm.mpdemo.ioformat;import java.io.IOException;import java.net.URI;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.SequenceFile;import org.apache.hadoop.io.SequenceFile.CompressionType;import org.apache.hadoop.io.Text;/** * desc: SequenceFileWriter * SequenceFileWriteDemo *  * @author chenwq (irwenqiang@gmail.com) * @version 1.0 2012/05/19 */public class SequenceFileWriteDemo {	private static final String[] DATA = { "One, two, buckle my shoe",			"Three, four, shut the door", "Five, six, pick up sticks",			"Seven, eight, lay them straight", "Nine, ten, a big fat hen" };	public static void main(String[] args) throws IOException {		String uri = args[0];		Configuration conf = new Configuration();		FileSystem fs = FileSystem.get(URI.create(uri), conf);		Path path = new Path(uri);		IntWritable key = new IntWritable();		Text value = new Text();		SequenceFile.Writer writer = null;		try {			/**			 * fs: outputstream			 * conf: configuration object			 * key: the key' type			 * value: the value's type			 */			writer = SequenceFile.createWriter(fs, conf, path, key.getClass(),					value.getClass());//			writer = SequenceFile.createWriter(fs, conf, path, key.getClass(),//					value.getClass(), CompressionType.BLOCK);			for (int i = 0; i < 100; i++) {				key.set(100 - i);				value.set(DATA[i % DATA.length]);				System.out.printf("[%s]\t%s\t%s\n", writer.getLength(), key,						value);				writer.append(key, value);			}		} finally {			IOUtils.closeStream(writer);		}	}}

package cn.edu.xmu.dm.mpdemo.ioformat;import java.io.IOException;import java.net.URI;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;import org.apache.hadoop.io.SequenceFile;import org.apache.hadoop.io.Writable;import org.apache.hadoop.util.ReflectionUtils;/** * desc: SequenceFileReader * SequenceFileReadDemo *  * @author chenwq (irwenqiang@gmail.com) * @version 1.0 2012/05/19 */public class SequenceFileReadDemo {	public static void main(String[] args) throws IOException {		String uri = args[0];		Configuration conf = new Configuration();		FileSystem fs = FileSystem.get(URI.create(uri), conf);		Path path = new Path(uri);		SequenceFile.Reader reader = null;		try {			reader = new SequenceFile.Reader(fs, path, conf);			Writable key = (Writable) ReflectionUtils.newInstance(					reader.getKeyClass(), conf);			Writable value = (Writable) ReflectionUtils.newInstance(					reader.getValueClass(), conf);			long position = reader.getPosition();			while (reader.next(key, value)) {				String syncSeen = reader.syncSeen() ? "*" : "";				System.out.printf("[%s%s]\t%s\t%s\n", position, syncSeen, key,						value);				position = reader.getPosition(); // beginning of next record			}		} finally {			IOUtils.closeStream(reader);		}	}}

使用Block压缩后的大小对比:

root@ubuntu:~# hadoop fs -ls mpdemo/Found 2 items-rw-r--r--   3 root supergroup       4788 2012-05-19 00:11 /user/root/mpdemo/seqinput-rw-r--r--   3 root supergroup        484 2012-05-19 00:17 /user/root/mpdemo/seqinputblock

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