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用java运行Hadoop例程报错:org.apache.hadoop.fs.LocalFileSystem cannot be cast to org.apache.所写代码如下:
package com.pcitc.hadoop; import java.io.IOException; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.hdfs.DistributedFileSystem; import org.apache.hadoop.hdfs.protocol.DatanodeInfo; /** * 获取HDFS集群上所有节点名称 * @author lenovo * */ public class GetList { public static void main(String[] args) throws IOException { Configuration conf = new Configuration(); conf.set("dfs.default.name", "hdfs://hadoopmaster:9000"); FileSystem fs = FileSystem.get(conf); DistributedFileSystem hdfs = (DistributedFileSystem) fs; DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats(); String[] names = new String[dataNodeStats.length]; for (int i = 0; i < dataNodeStats.length; i++) { names[i] = dataNodeStats[i].getHostName(); System.out.println("node" + i + "name" + names[i]); } } }
执行之后报如下错误:
Exception in thread "main" java.lang.ClassCastException: org.apache.hadoop.fs.LocalFileSystem cannot be cast to org.apache.hadoop.hdfs.DistributedFileSystem
at org.apache.hadoop.examples.FindFileOnHDFS.getHDFSNodes(FindFileOnHDFS.java:43)
at org.apache.hadoop.examples.FindFileOnHDFS.main(FindFileOnHDFS.java:16)
原因是DistributedFileSystem和LocalFileSystem都是FileSystem的子类，FileSystem.get(conf)得到的是LocalFileSystem的instance, 这个类型应该是默认的，要获得DistributedFileSystem，需要配置conf对象,按照我的写法我觉得应该是配了conf对象了，但是还是保存，最后按照网上的说法进行相应修改就可以了。直接上修改后的代码如下(注意红色部分):
package com.pcitc.hadoop; import java.io.IOException; import java.net.URI; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.hdfs.DistributedFileSystem; import org.apache.hadoop.hdfs.protocol.DatanodeInfo; /** * 获取HDFS集群上所有节点名称 * * @author lenovo * */ public class GetList { public static void main(String[] args) throws IOException { Configuration conf = new Configuration(); // conf.set("dfs.default.name", "hdfs://hadoopmaster:9000"); String uri = "hdfs://hadoopmaster:9000"; FileSystem fs = FileSystem.get(URI.create(uri), conf); DistributedFileSystem hdfs = (DistributedFileSystem) fs; DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats(); String[] names = new String[dataNodeStats.length]; for (int i = 0; i < dataNodeStats.length; i++) { names[i] = dataNodeStats[i].getHostName(); System.out.println("node:" + i + ",name:" + names[i]); } } }
用java运行Hadoop程序报错:org.apache.hadoop.fs.LocalFileSystem cannot be cast to org.apache.
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原文地址：http://www.cnblogs.com/longshiyVip/p/4811639.html
