Exception in thread "main" java.lang.NullPointerException

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1、在window作業系統上，使用eclipse開發工具從hdfsDistributed File System上下載檔案報null 指標異常解決方案：

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(Unknown Source)    at org.apache.hadoop.util.Shell.runCommand(Shell.java:482)    at org.apache.hadoop.util.Shell.run(Shell.java:455)    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:702)    at org.apache.hadoop.util.Shell.execCommand(Shell.java:791)    at org.apache.hadoop.util.Shell.execCommand(Shell.java:774)    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:646)    at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:472)    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:460)    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:426)    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:906)    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:887)    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:784)    at org.apache.hadoop.fs.FileUtil.copy(FileUtil.java:365)    at org.apache.hadoop.fs.FileUtil.copy(FileUtil.java:338)    at org.apache.hadoop.fs.FileUtil.copy(FileUtil.java:289)    at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:1968)    at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:1937)    at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:1913)    at com.bie.hadoop.crud.TextCreateNewFile.copyToLocalFile(TextCreateNewFile.java:191)    at com.bie.hadoop.crud.TextCreateNewFile.main(TextCreateNewFile.java:239)

2、將hadoop-2.5.0-cdh5.3.6.tar.gz檔案在window作業系統解壓縮，配置好環境變數。

然後驗證一下是否配置成功，操作如window+R，輸入cmd：

 

然後將如下所示的檔案hadoop-common-2.2.0-bin-32.rar解壓縮，然後全部複製放到hadoop-2.5.0-cdh5.3.6.tar.gz的bin目錄下面即可：

最後重啟電腦，運行下載程式，解決問題，或者在程式中配置如下所示內容：

System.setProperty("hadoop.home.dir","D:/biexiansheng/hadoop/hadoop-2.5.0-cdh5.3.6");

/*** * 擷取到配置資訊 * @return */public static Configuration getConfiguration(){    Configuration conf = new Configuration();    conf.set("fs.defaultFS", "hdfs://192.168.19.131:9000");    //重啟機器或者設定這個值    //System.setProperty("hadoop.home.dir","D:/biexiansheng/hadoop/hadoop-2.5.0-cdh5.3.6");    return conf;}

 

Exception in thread "main" java.lang.NullPointerException