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/**
* 下载文件
*/
@Test
public void download() throws Exception {
fs.copyToLocalFile(new Path("hdfs://master:9000/aa/lidunhui.jpg"), new Path("e://wangbadan.txt"));
}运行该下载测试报空指针异常，如下：
java.lang.NullPointerException at java.lang.ProcessBuilder.start(ProcessBuilder.java:1010) at org.apache.hadoop.util.Shell.runCommand(Shell.java:445) at org.apache.hadoop.util.Shell.run(Shell.java:418) at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:650) at org.apache.hadoop.util.Shell.execCommand(Shell.java:739) at org.apache.hadoop.util.Shell.execCommand(Shell.java:722) at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:633) at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:467) at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:456) at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:424) 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.jasun.hadoop.hdfs.HdfsUtil.download(HdfsUtil.java:62) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
解决办法，如下：
将fs.copyToLocalFile( hdfsPath,localPath);改为fs.copyToLocalFile( false,hdfsPath,localPath,true)
/**
* 下载文件
*/
@Test
public void download() throws Exception {
fs.copyToLocalFile(false, new Path("hdfs://master:9000/aa/lidunhui.jpg"), new Path("e://wangbadan.txt"), true);
}关于hadoop中用copyToLocalFile方法下载报NullPointerException该怎么办就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。
