dataload.HDFSReaderExternal.java Source code

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Here is the source code for dataload.HDFSReaderExternal.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dataload;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

/**
 * 
 * Helper class to read files from HDFS. Given the HDFS path it will read the file, and put each text line into an arraylist. The arraylist will then
 * be returned after the class is finished parsing the file. The XML configuration files will need to be present in the src folder so that they can
 * be read by this class. This is necessary so that the code has to information to link to the Hadoop cluster. Necessary XML files typically should
 * include core-site.xml, hdfs-site.xml, and mapred-site.xml. This will only work if the Hadoop cluster allows external access to HDFS, if not then
 * another implementations of HDFSRead needs to be written to access HDFS.
 * 
 * @author stakiar
 */
public class HDFSReaderExternal implements HDFSReader {

    public ArrayList<String> readFile(String fileName) throws FileNotFoundException {
        ArrayList<String> output = new ArrayList<String>();
        try {
            Configuration conf = new Configuration();

            FileSystem hdfs = FileSystem.get(java.net.URI.create(fileName), conf);
            FSDataInputStream in = hdfs.open(new Path(fileName));

            BufferedReader br = new BufferedReader(new InputStreamReader(in));
            String strLine;

            while ((strLine = br.readLine()) != null) {
                System.out.println(strLine);
                output.add(strLine);
            }
            hdfs.close();
        } catch (IOException e) {
            e.printStackTrace();
            System.err.println("Error: " + e.getMessage());
        }
        return output;
    }

    /**
     * Main method is used as a testing mechanism. Run this class and change the parameter to readFile() in order to test to see if this is working.
     * If no file is printed in console then the class is not accessing the Hadoop Grid properly.
     */
    public static void main(String args[]) {
        HDFSReaderExternal read = new HDFSReaderExternal();
        try {
            for (String s : read.readFile(args[0])) {
                System.out.println(s);
            }
        } catch (FileNotFoundException e) {
            System.err.println(e);
            System.err.println(e.getStackTrace());
        }
    }
}