Window7中Eclipse运行MapReduce程序报错的问题

按照文档：http://www.micmiu.com/bigdata/hadoop/hadoop2x-eclipse-mapreduce-demo/安装配置好Eclipse后，运行WordCount程序报错：

log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" java.lang.NullPointerException
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1011)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:404)
    at org.apache.hadoop.util.Shell.run(Shell.java:379)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:589)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:678)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:661)
    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:639)
    at org.apache.hadoop.fs.RawLocalFileSystem.mkdirs(RawLocalFileSystem.java:435)
    at org.apache.hadoop.fs.FilterFileSystem.mkdirs(FilterFileSystem.java:277)
    at org.apache.hadoop.mapreduce.JobSubmissionFiles.getStagingDir(JobSubmissionFiles.java:125)
    at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:344)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1268)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1265)
    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:1491)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:1265)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1286)
    at com.telchina.hadoop.WordCount.main(WordCount.java:84)

经过google，发现http://www.uniorder.com/2014/03/31/%E5%9C%A8%20Windows%20%E4%B8%8A%E4%BD%BF%E7%94%A8%20Eclipse%20%E8%BF%9C%E7%A8%8B%E8%B0%83%E8%AF%95%20Hadoop%202.2%20MapReduce%20%E7%A8%8B%E5%BA%8F/中：

下载 Hadoop 2.2 到你的 Windows 机器上（我是 Windows 7）并设置环境变量：HADOOP_HOME=你的Hadoop所在目录，再在Path中加入%HADOOP_HOME%in;。此时还没有完成。你需要去下载一些文件覆盖 Hadoop/bin 下的所有文件（戳这里）。

问题解决。

作者：sdjnzqr
出处：http://www.cnblogs.com/sdjnzqr/
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