使用 hadoop MiniDFSCluster 时出现 javax.management.InstanceAlreadyExistsException

Question

我正在使用 MiniDFSCluster 进行 junit 测试。现在我只是启动和关闭集群，junit 运行绿色。但我得到这个异常(exception):

javax.management.InstanceAlreadyExistsException: MXBean already registered with name Hadoop:service=NameNode,name=MetricsSystem,sub=Control
at com.sun.jmx.mbeanserver.MXBeanLookup.addReference(MXBeanLookup.java:120)
at com.sun.jmx.mbeanserver.MXBeanSupport.register(MXBeanSupport.java:143)
at com.sun.jmx.mbeanserver.MBeanSupport.preRegister2(MBeanSupport.java:183)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerDynamicMBean(DefaultMBeanServerInterceptor.java:941)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerObject(DefaultMBeanServerInterceptor.java:917)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:312)
at com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:482)
at org.apache.hadoop.metrics2.util.MBeans.register(MBeans.java:56)
at org.apache.hadoop.metrics2.impl.MetricsSystemImpl.initSystemMBean(MetricsSystemImpl.java:500)
at org.apache.hadoop.metrics2.impl.MetricsSystemImpl.init(MetricsSystemImpl.java:140)
at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.init(DefaultMetricsSystem.java:40)
at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.initialize(DefaultMetricsSystem.java:50)
at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1483)
at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1459)
at org.apache.hadoop.hdfs.MiniDFSCluster.startDataNodes(MiniDFSCluster.java:417)
at org.apache.hadoop.hdfs.MiniDFSCluster.<init>(MiniDFSCluster.java:280)
at org.apache.hadoop.hdfs.MiniDFSCluster.<init>(MiniDFSCluster.java:124)
at com.myCompany.TestAll.testInit(TestAll.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at junit.framework.TestCase.runTest(TestCase.java:168)
at junit.framework.TestCase.runBare(TestCase.java:134)
at junit.framework.TestResult$1.protect(TestResult.java:110)
at junit.framework.TestResult.runProtected(TestResult.java:128)
at junit.framework.TestResult.run(TestResult.java:113)
at junit.framework.TestCase.run(TestCase.java:124)
at junit.framework.TestSuite.runTest(TestSuite.java:232)
at junit.framework.TestSuite.run(TestSuite.java:227)
at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

谁能给我一些关于这个异常(exception)的建议吗？

非常感谢。

Answer 1

发生的事情是 hadoop 正在注册一个 jmx bean用于监控。 hadoop第一次启动时注册了bean，但是hadoop第二次启动时已经注册了同名的bean，导致出现上述错误。

要么您没有正确关闭 MiniDFSCluster，要么多次启动它，要么 MiniDFSCluster 中存在导致无法正确清理的错误。

您是否在拆卸方法中调用了 cluster.shutdown()，如所演示的 here .