Eclipse运行WordCount.java报错ClassNotFoundException，是为什么呢？

14/12/06 10:41:58 WARN mapred.JobClient: No job jar file set.  User classes may not be found. See JobConf(Class) or JobConf#setJar(String).
14/12/06 10:41:58 INFO input.FileInputFormat: Total input paths to process : 2
14/12/06 10:41:58 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
14/12/06 10:41:58 WARN snappy.LoadSnappy: Snappy native library not loaded
14/12/06 10:42:00 INFO mapred.JobClient: Running job: job_201412062143_0002
14/12/06 10:42:01 INFO mapred.JobClient:  map 0% reduce 0%
14/12/06 10:42:11 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000000_0, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:14 WARN mapred.JobClient: Error reading task outputworker3
14/12/06 10:42:14 WARN mapred.JobClient: Error reading task outputworker3
14/12/06 10:42:15 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000001_0, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:17 WARN mapred.JobClient: Error reading task outputworker2
14/12/06 10:42:17 WARN mapred.JobClient: Error reading task outputworker2
14/12/06 10:42:18 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000000_1, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:21 WARN mapred.JobClient: Error reading task outputworker4
14/12/06 10:42:21 WARN mapred.JobClient: Error reading task outputworker4
14/12/06 10:42:21 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000001_1, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:23 WARN mapred.JobClient: Error reading task outputworker5
14/12/06 10:42:23 WARN mapred.JobClient: Error reading task outputworker5
14/12/06 10:42:24 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000000_2, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:27 WARN mapred.JobClient: Error reading task outputworker1
14/12/06 10:42:27 WARN mapred.JobClient: Error reading task outputworker1
14/12/06 10:42:27 INFO mapred.JobClient: Task Id : attempt_201412062143_0002_m_000001_2, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:849)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.examples.WordCount$TokenizerMapper
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:802)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:847)
... 8 more

14/12/06 10:42:29 WARN mapred.JobClient: Error reading task outputworker3
14/12/06 10:42:29 WARN mapred.JobClient: Error reading task outputworker3
14/12/06 10:42:32 INFO mapred.JobClient: Job complete: job_201412062143_0002
14/12/06 10:42:33 INFO mapred.JobClient: Counters: 8
14/12/06 10:42:33 INFO mapred.JobClient: Job Counters
14/12/06 10:42:33 INFO mapred.JobClient:    SLOTS_MILLIS_MAPS=50780
14/12/06 10:42:33 INFO mapred.JobClient:    Total time spent by all reduces waiting after reserving slots (ms)=0
14/12/06 10:42:33 INFO mapred.JobClient:    Total time spent by all maps waiting after reserving slots (ms)=0
14/12/06 10:42:33 INFO mapred.JobClient:    Rack-local map tasks=7
14/12/06 10:42:33 INFO mapred.JobClient:    Launched map tasks=8
14/12/06 10:42:33 INFO mapred.JobClient:    Data-local map tasks=1
14/12/06 10:42:33 INFO mapred.JobClient:    SLOTS_MILLIS_REDUCES=0
14/12/06 10:42:33 INFO mapred.JobClient:    Failed map tasks=1