Hadoop 运行jar包时 java.lang.ClassNotFoundException: Class com.zhen.mr.RunJob$HotMapper not found

错误如下

Error: java.lang.RuntimeException: java.lang.ClassNotFoundException: Class com.zhen.mr.RunJob$HotMapper not found
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2154)
    at org.apache.hadoop.mapreduce.task.JobContextImpl.getMapperClass(JobContextImpl.java:186)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:742)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:163)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1692)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)
Caused by: java.lang.ClassNotFoundException: Class com.zhen.mr.RunJob$HotMapper not found
    at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:2060)
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2152)
    ... 8 more

错误出现之前还有警告提示，如下

 WARN mapreduce.JobResourceUploader: No job jar file set.  User classes may not be found. See Job or Job#setJar(String).

提示说没有设置job jar

解决方法：

代码中给job对象set一下

job.setJarByClass(RunJob.class);

然后再打包运行就ok了。