use hadoop fs api to read file in case of hadoop namenode HA (QJM)

HdfsReader.java

package com.hadoop.hdfs.reader;

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class HdfsReader extends Configured implements Tool {

    public static final String FS_PARAM_NAME = "fs.defaultFS";

    public int run(String[] args) throws Exception {

        if (args.length < 2) {
            System.err.println("HdfsReader [hdfs input path] [local output path]");
            return 1;
        }

        Path inputPath = new Path(args[0]);
        String localOutputPath = args[1];
        //Configuration conf = getConf();
	Configuration conf = new Configuration(false);
    	conf.set("fs.defaultFS", "hdfs://yourclustername");
    	conf.set("fs.default.name", conf.get("fs.defaultFS"));
    	conf.set("dfs.nameservices","yourclustername");
    	conf.set("dfs.ha.namenodes.yourclustername", "nn1,nn2");
    	conf.set("dfs.namenode.rpc-address.yourclustername.nn1","hadoop01.yourclustername:8020");
    	conf.set("dfs.namenode.rpc-address.yourclustername.nn2", "hadoop07.yourclustername:8020");
    	conf.set("dfs.client.failover.proxy.provider.yourclustername","org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider");

        System.out.println("configured filesystem = " + conf.get(FS_PARAM_NAME));
        FileSystem fs = FileSystem.get(conf);
        InputStream is = fs.open(inputPath);
        OutputStream os = new BufferedOutputStream(new FileOutputStream(localOutputPath));
        IOUtils.copyBytes(is, os, conf);
        return 0;
    }

    public static void main( String[] args ) throws Exception {
        int returnCode = ToolRunner.run(new HdfsReader(), args);
        System.exit(returnCode);
    }
}

add the export to /etc/profile

export CLASSPATH=/usr/hdp/2.4.0.0-169/hadoop/hadoop-common.jar:/usr/hdp/2.4.0.0-169/hadoop-mapreduce/hadoop-mapreduce-client-core.jar:/usr/hdp/2.4.0.0-169/hadoop/client/commons-cli.jar

and source /etc/profile

and run the following command

javac HdfsReader.java -d hdfs

jar cvf HdfsReader.jar -C hdfs .

hadoop jar HdfsReader.jar com.hadoop.hdfs.reader.HdfsReader /tmp/ida8c04a64_date462516 ./hello_output