Window7中Eclipse運行MapReduce程式報錯的問題

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按照文檔：http://www.micmiu.com/bigdata/hadoop/hadoop2x-eclipse-mapreduce-demo/安裝配置好Eclipse後，運行WordCount程式報錯：

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)

經過google，發現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：

下載 Hadoop 2.2 到你的 Windows 機器上（我是 Windows 7）並設定環境變數：HADOOP_HOME=你的Hadoop所在目錄，再在Path中加入%HADOOP_HOME%\bin;。此時還沒有完成。你需要去下載一些檔案覆蓋 Hadoop/bin 下的所有檔案（戳這裡）。

問題解決。

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出處：http://www.cnblogs.com/sdjnzqr/
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