用fs.copyToLocalFile( hdfsPath,localPath);下载hdfs的文件会报NullPointerException,具体报错为:
java.lang.NullPointerException at java.lang.ProcessBuilder.start(ProcessBuilder.java:1012) at org.apache.hadoop.util.Shell.runCommand(Shell.java:487) at org.apache.hadoop.util.Shell.run(Shell.java:460) at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:720) at org.apache.hadoop.util.Shell.execCommand(Shell.java:813) at org.apache.hadoop.util.Shell.execCommand(Shell.java:796) at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:656) at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:490) at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:462) at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:428) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:908) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:889) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:786) 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:1970) at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:1939) at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:1915) at hadoop.downFile.downloadFileorDirectoryOnHDFS(downFile.java:29) at hadoop.downFile.main(downFile.java:12)
解决方法:将fs.copyToLocalFile( hdfsPath,localPath);改为fs.copyToLocalFile( false,hdfsPath,localPath,true);
原因:不理解,但加上这两个后确实可以下载
用java下载hdfs文件报NullPointerException
原文：http://www.cnblogs.com/zhuzhixijiang/p/5141454.html