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 Bye 3 Hello 3 Word 1 World 3 bye 1 hello 2 world 1
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