Call to localhost_127.0.0.1_9000 failed on connection exception_java.net.ConnectException的解决方案.html

<h1 style="text-align: center;">Call to localhost/127.0.0.1:9000 failed on connection exception:java.net.ConnectException的解决方案</h1>
<h4 class="postTitle">作者：凯鲁嘎吉 - 博客园&nbsp;<a href="http://www.cnblogs.com/kailugaji/" target="_blank">http://www.cnblogs.com/kailugaji/</a></h4>
<p><span style="font-size: 16px;">在启动hadoop时，出现了如下错误：</span></p>
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<pre class="brush:javascript;gutter:true;">Call From java.net.UnknownHostException: ubuntu-larntin: ubuntu-larntin to localhost:9000 failed on connection exception: java.net.ConnectException: Connection refused;
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<p><span style="font-size: 16px;">而且启动datanode、yarn都正常，只有namenode一直挂掉</span></p>
<p><span style="font-size: 16px;">解决方案如下：</span></p>
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<pre class="brush:javascript;gutter:true;">wrr@ubuntu:~$ hadoop namenode -format
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<p><span style="font-size: 16px;">之后，重新启动所有的集群，即可</span></p>
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<pre class="brush:javascript;gutter:true;">wrr@ubuntu:~$ cd /home/wrr/java/hadoop-2.7.6/sbin
wrr@ubuntu:~/java/hadoop-2.7.6/sbin$ ./hadoop-daemon.sh start namenode
starting namenode, logging to /home/wrr/java/hadoop-2.7.6/logs/hadoop-wrr-namenode-ubuntu.out
wrr@ubuntu:~/java/hadoop-2.7.6/sbin$ jps
8307 DataNode
9317 NameNode
7431 
9352 Jps
8476 ResourceManager
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<p><span style="font-size: 16px;">之后，再次在eclipse上运行程序，就没问题了。</span></p>
<p><span style="font-size: 16px;">新建了一个java文件</span></p>
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<pre class="brush:java;gutter:true;">import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class HDFSFileIfExist {
    public static void main(String[] args){
        try{
            String fileName = "test";
            Configuration conf = new Configuration();
            conf.set("fs.defaultFS", "hdfs://localhost:9000");
            conf.set("fs.hdfs.impl", "org.apache.hadoop.hdfs.DistributedFileSystem");
            FileSystem fs = FileSystem.get(conf);
            if(fs.exists(new Path(fileName))){
                System.out.println("文件存在");
            }else{
                System.out.println("文件不存在");
            }
 
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}
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<p><span style="font-size: 16px;">判断当前hadoop-2.7.6目录下是否存在test文件</span></p>
<p><img style="display: block; margin-left: auto; margin-right: auto;" src="https://img2018.cnblogs.com/blog/1027447/201812/1027447-20181220171608696-726491478.png" alt="" /></p>
<p><span style="font-size: 16px;">如果想看更多关于java API的内容，可以看<a href="http://dblab.xmu.edu.cn/blog/290-2/" target="_blank">大数据技术原理与应用 第三章 分布式文件系统HDFS 学习指南_厦大数据库实验室博客</a></span></p>
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