环境：Vmware 8.0 和Ubuntu11.04

Hadoop 实战之MapReduce链接作业之预处理

第一步：首先创建一个工程命名为HadoopTest.目录结构如下图:


第二步: 在/home/tanglg1987目录下新建一个start.sh脚本文件，每次启动虚拟机都要删除/tmp目录下的全部文件，重新格式化namenode，代码如下： 

sudo rm -rf /tmp/*
rm -rf /home/tanglg1987/hadoop-0.20.2/logs
hadoop namenode -format
hadoop datanode -format
start-all.sh
hadoop fs -mkdir input 
hadoop dfsadmin -safemode leave

第三步：给start.sh增加执行权限并启动hadoop伪分布式集群，代码如下: 
chmod 777 /home/tanglg1987/ start.sh
./start.sh

执行过程如下：

12/10/15 23:05:38 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = tanglg1987/127.0.1.1
STARTUP_MSG: args = [-format]
STARTUP_MSG: version = 0.20.2
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010
************************************************************/
12/10/15 23:05:39 INFO namenode.FSNamesystem: fsOwner=tanglg1987,tanglg1987,adm,dialout,cdrom,plugdev,lpadmin,admin,sambashare
12/10/15 23:05:39 INFO namenode.FSNamesystem: supergroup=supergroup
12/10/15 23:05:39 INFO namenode.FSNamesystem: isPermissionEnabled=true
12/10/15 23:05:39 INFO common.Storage: Image file of size 100 saved in 0 seconds.
12/10/15 23:05:39 INFO common.Storage: Storage directory /tmp/hadoop-tanglg1987/dfs/name has been successfully formatted.
12/10/15 23:05:39 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at tanglg1987/127.0.1.1
************************************************************/
12/10/15 23:05:40 INFO datanode.DataNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG: host = tanglg1987/127.0.1.1
STARTUP_MSG: args = [-format]
STARTUP_MSG: version = 0.20.2
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010
************************************************************/
Usage: java DataNode
[-rollback]
12/10/15 23:05:40 INFO datanode.DataNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down DataNode at tanglg1987/127.0.1.1
************************************************************/
starting namenode, logging to /home/tanglg1987/hadoop-0.20.2/bin/../logs/hadoop-tanglg1987-namenode-tanglg1987.out
localhost: starting datanode, logging to /home/tanglg1987/hadoop-0.20.2/bin/../logs/hadoop-tanglg1987-datanode-tanglg1987.out
localhost: starting secondarynamenode, logging to /home/tanglg1987/hadoop-0.20.2/bin/../logs/hadoop-tanglg1987-secondarynamenode-tanglg1987.out
starting jobtracker, logging to /home/tanglg1987/hadoop-0.20.2/bin/../logs/hadoop-tanglg1987-jobtracker-tanglg1987.out
localhost: starting tasktracker, logging to /home/tanglg1987/hadoop-0.20.2/bin/../logs/hadoop-tanglg1987-tasktracker-tanglg1987.out
Safe mode is OFF

第四步：上传本地文件到hdfs

在/home/tanglg1987目录下新建Customer.txt内容如下：

100	tom 90
101	mary 85
102	kate 60

上传本地文件到hdfs：

hadoop fs -put /home/tanglg1987/ChainMapper.txt input

第五步：新建一个ChainMapperDemo.java，代码如下：

package com.baison.action;
import java.io.IOException;
import java.util.*;
import java.lang.String;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;
import org.apache.hadoop.mapred.lib.*;
public class ChainMapperDemo {
	public static class Map00 extends MapReduceBase implements
			Mapper<Text, Text, Text, Text> {
		public void map(Text key, Text value, OutputCollector output,
				Reporter reporter) throws IOException {
			Text ft = new Text("100");
			if (!key.equals(ft)) {
				output.collect(key, value);
			}
		}
	}
	public static class Map01 extends MapReduceBase implements
			Mapper<Text, Text, Text, Text> {
		public void map(Text key, Text value, OutputCollector output,
				Reporter reporter) throws IOException {
			Text ft = new Text("101");
			if (!key.equals(ft)) {
				output.collect(key, value);
			}
		}
	}
	public static class Reduce extends MapReduceBase implements
			Reducer<Text, Text, Text, Text> {
		public void reduce(Text key, Iterator values, OutputCollector output,
				Reporter reporter) throws IOException {
			while (values.hasNext()) {
				output.collect(key, values.next());
			}

		}
	}
	public static void main(String[] args) throws Exception {
		String[] arg = { "hdfs://localhost:9100/user/tanglg1987/input/ChainMapper.txt",
				"hdfs://localhost:9100/user/tanglg1987/output" };
		JobConf conf = new JobConf(ChainMapperDemo.class);
		conf.setJobName("ChainMapperDemo");
		conf.setInputFormat(KeyValueTextInputFormat.class);
		conf.setOutputFormat(TextOutputFormat.class);
		ChainMapper cm = new ChainMapper();
		JobConf mapAConf = new JobConf(false);
		cm.addMapper(conf, Map00.class, Text.class, Text.class, Text.class,
				Text.class, true, mapAConf);
		JobConf mapBConf = new JobConf(false);
		cm.addMapper(conf, Map01.class, Text.class, Text.class, Text.class,
				Text.class, true, mapBConf);
		conf.setReducerClass(Reduce.class);
		conf.setOutputKeyClass(Text.class);
		conf.setOutputValueClass(Text.class);
		FileInputFormat.setInputPaths(conf, new Path(arg[0]));
		FileOutputFormat.setOutputPath(conf, new Path(arg[1]));
		JobClient.runJob(conf);
	}
}

第六步：Run On Hadoop，运行过程如下：

12/10/17 21:05:53 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
12/10/17 21:05:53 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
12/10/17 21:05:53 WARN mapred.JobClient: No job jar file set. User classes may not be found. See JobConf(Class) or JobConf#setJar(String).
12/10/17 21:05:54 INFO mapred.FileInputFormat: Total input paths to process : 1
12/10/17 21:05:54 INFO mapred.JobClient: Running job: job_local_0001
12/10/17 21:05:54 INFO mapred.FileInputFormat: Total input paths to process : 1
12/10/17 21:05:54 INFO mapred.MapTask: numReduceTasks: 1
12/10/17 21:05:54 INFO mapred.MapTask: io.sort.mb = 100
12/10/17 21:05:54 INFO mapred.MapTask: data buffer = 79691776/99614720
12/10/17 21:05:54 INFO mapred.MapTask: record buffer = 262144/327680
12/10/17 21:05:54 INFO mapred.MapTask: Starting flush of map output
12/10/17 21:05:54 INFO mapred.MapTask: Finished spill 0
12/10/17 21:05:54 INFO mapred.TaskRunner: Task:attempt_local_0001_m_000000_0 is done. And is in the process of commiting
12/10/17 21:05:54 INFO mapred.LocalJobRunner: hdfs://localhost:9100/user/tanglg1987/input/ChainMapper.txt:0+35
12/10/17 21:05:54 INFO mapred.TaskRunner: Task 'attempt_local_0001_m_000000_0' done.
12/10/17 21:05:54 INFO mapred.LocalJobRunner:
12/10/17 21:05:54 INFO mapred.Merger: Merging 1 sorted segments
12/10/17 21:05:54 INFO mapred.Merger: Down to the last merge-pass, with 1 segments left of total size: 16 bytes
12/10/17 21:05:54 INFO mapred.LocalJobRunner:
12/10/17 21:05:54 INFO mapred.TaskRunner: Task:attempt_local_0001_r_000000_0 is done. And is in the process of commiting
12/10/17 21:05:54 INFO mapred.LocalJobRunner:
12/10/17 21:05:54 INFO mapred.TaskRunner: Task attempt_local_0001_r_000000_0 is allowed to commit now
12/10/17 21:05:54 INFO mapred.FileOutputCommitter: Saved output of task 'attempt_local_0001_r_000000_0' to hdfs://localhost:9100/user/tanglg1987/output
12/10/17 21:05:54 INFO mapred.LocalJobRunner: reduce > reduce
12/10/17 21:05:54 INFO mapred.TaskRunner: Task 'attempt_local_0001_r_000000_0' done.
12/10/17 21:05:55 INFO mapred.JobClient: map 100% reduce 100%
12/10/17 21:05:55 INFO mapred.JobClient: Job complete: job_local_0001
12/10/17 21:05:55 INFO mapred.JobClient: Counters: 15
12/10/17 21:05:55 INFO mapred.JobClient: FileSystemCounters
12/10/17 21:05:55 INFO mapred.JobClient: FILE_BYTES_READ=36152
12/10/17 21:05:55 INFO mapred.JobClient: HDFS_BYTES_READ=70
12/10/17 21:05:55 INFO mapred.JobClient: FILE_BYTES_WRITTEN=73202
12/10/17 21:05:55 INFO mapred.JobClient: HDFS_BYTES_WRITTEN=12
12/10/17 21:05:55 INFO mapred.JobClient: Map-Reduce Framework
12/10/17 21:05:55 INFO mapred.JobClient: Reduce input groups=1
12/10/17 21:05:55 INFO mapred.JobClient: Combine output records=0
12/10/17 21:05:55 INFO mapred.JobClient: Map input records=3
12/10/17 21:05:55 INFO mapred.JobClient: Reduce shuffle bytes=0
12/10/17 21:05:55 INFO mapred.JobClient: Reduce output records=1
12/10/17 21:05:55 INFO mapred.JobClient: Spilled Records=2
12/10/17 21:05:55 INFO mapred.JobClient: Map output bytes=12
12/10/17 21:05:55 INFO mapred.JobClient: Map input bytes=35
12/10/17 21:05:55 INFO mapred.JobClient: Combine input records=0
12/10/17 21:05:55 INFO mapred.JobClient: Map output records=1
12/10/17 21:05:55 INFO mapred.JobClient: Reduce input records=1

第七步：查看结果集，运行结果如下：

# hadoop # mapreduce
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