Java API访问HA方式的HDFS

1、介绍

对于namenode是HA高可用集群时，客户端远程访问hdfs有两种实现方法： 

（1）将所有关于namenode的参数写入Configuration对象中 

（2）将配置文件core-site.xml和hdfs-site.xml文件复制到项目的src目录下

2、方式一

（1）样例代码

import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
 
public class HADemo { 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://my");
        conf.set("dfs.nameservices", "my");
        conf.set("dfs.ha.namenodes.my", "nn1,nn2");
        conf.set("dfs.namenode.rpc-address.my.nn1", "192.168.12.156:8020");
        conf.set("dfs.namenode.rpc-address.my.nn2", "192.168.157:8020");
        conf.set("dfs.client.failover.proxy.provider.my", "org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider");

        try {
            FileSystem fs = FileSystem.get(new URI("hdfs://my"), conf,"root");
            boolean b=fs.mkdirs(new Path("/a"));
            System.out.println(b);
            fs.copyFromLocalFile(new Path("D:\\a.txt"), new Path("/a/a.txt"));
            fs.close();
        } catch (Exception e) {
            System.out.println(e);
        }
    }

}

（2）运行结果

log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).

log4j:WARN Please initialize the log4j system properly.

log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

true 

（3）HDFS命令验证

[root@node1 ~]# hdfs dfs -ls /a

Found 2 items

-rw-r--r--   3 root supergroup         13 2018-08-08 09:11 /a/a.txt

[root@node1 ~]# hdfs dfs -cat /a/a.txt

Hello,Hadoop!

[root@node1 ~]#