HADOOP :: java.lang.ClassNotFoundException: WordCount

2022-01-13 00:00:00 hadoop mapreduce classnotfoundexception java

我正在使用 eclipse 导出 map-reduce 程序的 jar 文件.当我使用命令运行 jar 时

I am using eclipse to export the jar file of a map-reduce program. When i am run the jar using command 

 hadoop jar hadoop-prog.jar WordCount /home/temp/input /home/temp/output

它总是显示错误:

   Exception in thread "main" java.lang.ClassNotFoundException: WordCount
    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 java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:247)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:149)

顺便说一句，我从互联网上得到了一个 wordcount 示例 jar 文件，它运行得很好.

Btw, I get a sample example jar file of wordcount from internet and it ran very well.

我不知道问题出在哪里.

I could not figure out where is the problem.

推荐答案

如果您尝试运行示例中提供的字数，您应该运行:

If you're trying to run the wordcount provided in the examples, you should run:

hadoop jar hadoop*examples*.jar wordcount /home/temp/input /home/temp/output

有关如何在 这个链接.

一般来说，如果您正在开发自己的 Map/Reduce 作业，则应包含驱动程序类的完整包名，这样可能会起作用:

In general, if you're developing your own Map/Reduce jobs, you should include the full package name of your driver class, so something like this might work:

hadoop jar wordcount.jar com.something.WordCount /home/temp/input /home/temp/output

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