Hadoop示例程序WordCount编译运行
首先确保Hadoop已正确安装及运行。
将WordCount.java拷贝出来
$ cp ./src/examples/org/apache/hadoop/examples/WordCount.java /home/hadoop/
在当前目录下创建一个存放WordCount.class的文件夹
$ mkdir class
编译WordCount.java
$ javac -classpath /usr/local/hadoop/hadoop-core-0.20.203.0.jar:/usr/local/hadoop/lib/commons-cli-1.2.jar WordCount.java -d class
编译完成后class文件夹下会出现一个org文件夹
$ ls class
org
对编译好的class打包
$ cd class
$ jar cvf WordCount.jar *
已添加清单
正在添加: org/(输入 = 0) (输出 = 0)(存储了 0%)
正在添加: org/apache/(输入 = 0) (输出 = 0)(存储了 0%)
正在添加: org/apache/hadoop/(输入 = 0) (输出 = 0)(存储了 0%)
正在添加: org/apache/hadoop/examples/(输入 = 0) (输出 = 0)(存储了 0%)
正在添加: org/apache/hadoop/examples/WordCount$TokenizerMapper.class(输入 = 1790) (输出 = 765)(压缩了 57%)
正在添加: org/apache/hadoop/examples/WordCount$IntSumReducer.class(输入 = 1793) (输出 = 746)(压缩了 58%)
正在添加: org/apache/hadoop/examples/WordCount.class(输入 = 1911) (输出 = 996)(压缩了 47%)
至此java文件的编译工作已经完成
准备测试文件，启动Hadoop。
由于运行Hadoop时指定的输入文件只能是HDFS文件系统里的文件，所以我们必须将要测试的文件从本地文件系统拷贝到HDFS文件系统中。
$ hadoop fs -mkdir input
$ hadoop fs -ls
Found 1 items
drwxr-xr-x - hadoop supergroup 0 2014-03-26 10:39 /user/hadoop/input
$ hadoop fs -put file input
$ hadoop fs -ls input
Found 1 items
-rw-r--r-- 2 hadoop supergroup 75 2014-03-26 10:40 /user/hadoop/input/file
运行程序
$ cd class
$ ls
org WordCount.jar
$ hadoop jar WordCount.jar org.apache.hadoop.examples.WordCount input output
14/03/26 10:57:39 INFO input.FileInputFormat: Total input paths to process : 1
14/03/26 10:57:40 INFO mapred.JobClient: Running job: job_201403261015_0001
14/03/26 10:57:41 INFO mapred.JobClient: map 0% reduce 0%
14/03/26 10:57:54 INFO mapred.JobClient: map 100% reduce 0%
14/03/26 10:58:06 INFO mapred.JobClient: map 100% reduce 100%
14/03/26 10:58:11 INFO mapred.JobClient: Job complete: job_201403261015_0001
14/03/26 10:58:11 INFO mapred.JobClient: Counters: 25
14/03/26 10:58:11 INFO mapred.JobClient: Job Counters
14/03/26 10:58:11 INFO mapred.JobClient: Launched reduce tasks=1
14/03/26 10:58:11 INFO mapred.JobClient: SLOTS_MILLIS_MAPS=12321
14/03/26 10:58:11 INFO mapred.JobClient: Total time spent by all reduces waiting after reserving slots (ms)=0
14/03/26 10:58:11 INFO mapred.JobClient: Total time spent by all maps waiting after reserving slots (ms)=0
14/03/26 10:58:11 INFO mapred.JobClient: Launched map tasks=1
14/03/26 10:58:11 INFO mapred.JobClient: Data-local map tasks=1
14/03/26 10:58:11 INFO mapred.JobClient: SLOTS_MILLIS_REDUCES=10303
14/03/26 10:58:11 INFO mapred.JobClient: File Output Format Counters
14/03/26 10:58:11 INFO mapred.JobClient: Bytes Written=51
14/03/26 10:58:11 INFO mapred.JobClient: FileSystemCounters
14/03/26 10:58:11 INFO mapred.JobClient: FILE_BYTES_READ=85
14/03/26 10:58:11 INFO mapred.JobClient: HDFS_BYTES_READ=184
14/03/26 10:58:11 INFO mapred.JobClient: FILE_BYTES_WRITTEN=42541
14/03/26 10:58:11 INFO mapred.JobClient: HDFS_BYTES_WRITTEN=51
14/03/26 10:58:11 INFO mapred.JobClient: File Input Format Counters
14/03/26 10:58:11 INFO mapred.JobClient: Bytes Read=75
14/03/26 10:58:11 INFO mapred.JobClient: Map-Reduce Framework
14/03/26 10:58:11 INFO mapred.JobClient: Reduce input groups=7
14/03/26 10:58:11 INFO mapred.JobClient: Map output materialized bytes=85
14/03/26 10:58:11 INFO mapred.JobClient: Combine output records=7
14/03/26 10:58:11 INFO mapred.JobClient: Map input records=1
14/03/26 10:58:11 INFO mapred.JobClient: Reduce shuffle bytes=0
14/03/26 10:58:11 INFO mapred.JobClient: Reduce output records=7
14/03/26 10:58:11 INFO mapred.JobClient: Spilled Records=14
14/03/26 10:58:11 INFO mapred.JobClient: Map output bytes=131
14/03/26 10:58:11 INFO mapred.JobClient: Combine input records=14
14/03/26 10:58:11 INFO mapred.JobClient: Map output records=14
14/03/26 10:58:11 INFO mapred.JobClient: SPLIT_RAW_BYTES=109
14/03/26 10:58:11 INFO mapred.JobClient: Reduce input records=7
查看结果
$ hadoop fs -ls
Found 2 items
drwxr-xr-x - hadoop supergroup 0 2014-03-26 10:40 /user/hadoop/input
drwxr-xr-x - hadoop supergroup 0 2014-03-26 10:58 /user/hadoop/output
可以发现hadoop中多了一个output文件，查看output中的文件信息
$ hadoop fs -ls output
Found 3 items
-rw-r--r-- 2 hadoop supergroup 0 2014-03-26 11:04 /user/hadoop/output/_SUCCESS
drwxr-xr-x - hadoop supergroup 0 2014-03-26 11:04 /user/hadoop/output/_logs
-rw-r--r-- 2 hadoop supergroup 65 2014-03-26 11:04 /user/hadoop/output/part-r-00000
查看运行结果
$ hadoop fs -cat output/part-r-00000
Bye3
Hello3
Word1
World3
bye1
hello2
world1
至此，Hadoop下WordCount示例运行结束。
如果还想运行一遍就需要把output文件夹删除，否则会报异常，如下
14/03/26 11:41:30 INFO mapred.JobClient: Cleaning up the staging area hdfs://localhost:9000/tmp/hadoop-hadoop/mapred/staging/hadoop/.staging/job_201403261015_0003
Exception in thread "main" org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory output already exists
at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:134)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:830)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:791)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059)
at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:791)
at org.apache.hadoop.mapreduce.Job.submit(Job.java:465)
at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:494)
at org.apache.hadoop.examples.WordCount.main(WordCount.java:67)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.apache.hadoop.util.RunJar.main(RunJar.java:156)
删除output文件夹操作如下
$ hadoop fs -rmr output
Deleted hdfs://localhost:9000/user/hadoop/output
也可以直接运行Hadoop示例中已经编译过的jar文件
$ hadoop jar /usr/local/hadoop/hadoop-examples-0.20.203.0.jar wordcount input output
14/03/28 17:02:33 INFO input.FileInputFormat: Total input paths to process : 2
14/03/28 17:02:33 INFO mapred.JobClient: Running job: job_201403281439_0004
14/03/28 17:02:34 INFO mapred.JobClient: map 0% reduce 0%
14/03/28 17:02:49 INFO mapred.JobClient: map 100% reduce 0%
14/03/28 17:03:01 INFO mapred.JobClient: map 100% reduce 100%
14/03/28 17:03:06 INFO mapred.JobClient: Job complete: job_201403281439_0004
14/03/28 17:03:06 INFO mapred.JobClient: Counters: 25
14/03/28 17:03:06 INFO mapred.JobClient: Job Counters
14/03/28 17:03:06 INFO mapred.JobClient: Launched reduce tasks=1
14/03/28 17:03:06 INFO mapred.JobClient: SLOTS_MILLIS_MAPS=17219
14/03/28 17:03:06 INFO mapred.JobClient: Total time spent by all reduces waiting after reserving slots (ms)=0
14/03/28 17:03:06 INFO mapred.JobClient: Total time spent by all maps waiting after reserving slots (ms)=0
14/03/28 17:03:06 INFO mapred.JobClient: Launched map tasks=2
14/03/28 17:03:06 INFO mapred.JobClient: Data-local map tasks=2
14/03/28 17:03:06 INFO mapred.JobClient: SLOTS_MILLIS_REDUCES=10398
14/03/28 17:03:06 INFO mapred.JobClient: File Output Format Counters
14/03/28 17:03:06 INFO mapred.JobClient: Bytes Written=65
14/03/28 17:03:06 INFO mapred.JobClient: FileSystemCounters
14/03/28 17:03:06 INFO mapred.JobClient: FILE_BYTES_READ=131
14/03/28 17:03:06 INFO mapred.JobClient: HDFS_BYTES_READ=343
14/03/28 17:03:06 INFO mapred.JobClient: FILE_BYTES_WRITTEN=63840
14/03/28 17:03:06 INFO mapred.JobClient: HDFS_BYTES_WRITTEN=65
14/03/28 17:03:06 INFO mapred.JobClient: File Input Format Counters
14/03/28 17:03:06 INFO mapred.JobClient: Bytes Read=124
14/03/28 17:03:06 INFO mapred.JobClient: Map-Reduce Framework
14/03/28 17:03:06 INFO mapred.JobClient: Reduce input groups=9
14/03/28 17:03:06 INFO mapred.JobClient: Map output materialized bytes=137
14/03/28 17:03:06 INFO mapred.JobClient: Combine output records=11
14/03/28 17:03:06 INFO mapred.JobClient: Map input records=2
14/03/28 17:03:06 INFO mapred.JobClient: Reduce shuffle bytes=85
14/03/28 17:03:06 INFO mapred.JobClient: Reduce output records=9
14/03/28 17:03:06 INFO mapred.JobClient: Spilled Records=22
14/03/28 17:03:06 INFO mapred.JobClient: Map output bytes=216
14/03/28 17:03:06 INFO mapred.JobClient: Combine input records=23
14/03/28 17:03:06 INFO mapred.JobClient: Map output records=23
14/03/28 17:03:06 INFO mapred.JobClient: SPLIT_RAW_BYTES=219
14/03/28 17:03:06 INFO mapred.JobClient: Reduce input records=11
参考资料：http://www.cnblogs.com/aukle/p/3214984.html
http://blog.csdn.net/turkeyzhou/article/details/8121601
http://www.cnblogs.com/xia520pi/archive/2012/05/16/2504205.html
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