参考链接：https://www.cnblogs.com/qifengshi/p/6036870.html
[root@Master /]# hadoop jar wordscount.jar WordCount Exception in thread "main" java.lang.ClassNotFoundException: WordCount at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:348) at org.apache.hadoop.util.RunJar.run(RunJar.java:214) at org.apache.hadoop.util.RunJar.main(RunJar.java:136)