转载自 Hadoop的FileSystem.copyToLocalFile两个参数 空指针异常

在网上一搜，直接改成fileSystem.copyToLocalFile（false，xx，xx，true）即可。

Exception in thread "main" java.lang.NullPointerExceptionat 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.beifeng.TestCopy.myCopyToLocal(TestCopy.java:44)at com.beifeng.TestCopy.main(TestCopy.java:15)

//fs.copyToLocalFile(new Path("/hadoop/put/111.txt"), new Path("e:/txt/copyFormHDFS.txt"));
fs.copyToLocalFile(false, new Path("/hadoop/put/111.txt"), new Path("e:/txt/copyFormHDFS.txt"),true);

但是基本上就这一句，也不说为啥，还是自己查API吧：

public void copyToLocalFile(boolean delSrc,Path src,Path dst,boolean useRawLocalFileSystem)throws IOExceptionThe src file is under this filesystem, and the dst is on the local disk. Copy it from the remote filesystem to the local dst name. 
delSrc indicates if the src will be removed or not. 
useRawLocalFileSystem indicates whether to use RawLocalFileSystem as the local file system or not. 
RawLocalFileSystem is non checksumming, So, It will not create any crc files at local.Parameters:
delSrc - whether to delete the src
src - path
dst - path
useRawLocalFileSystem - whether to use RawLocalFileSystem as local file system or not.Throws:
IOException - for any IO error

src文件位于此文件系统下，dst位于本地磁盘上。将其从远程文件系统复制到本地dst名称。delSrc指示src是否会被删除。useRawLocalFileSystem指示是否使用RawLocalFileSystem作为本地文件系统。RawLocalFileSystem不是校验和，所以它不会在本地创建任何crc文件。

delSrc : 是否删除src
useRawLocalFileSystem：是否使用RawLocalFileSystem作为本地文件系统。