HDFS FileSystems API example

FIleSystemOperations.java

package com.cloudwick.mapreduce.FileSystemAPI;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

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


/**
 * Simple Driver to read/write to hdfs
 * @author ashrith
 *
 */
public class FileSystemOperations {
  public FileSystemOperations() {

  }

  /**
   * create a existing file from local filesystem to hdfs
   * @param source
   * @param dest
   * @param conf
   * @throws IOException
   */
  public void addFile(String source, String dest, Configuration conf) throws IOException {

    FileSystem fileSystem = FileSystem.get(conf);

    // Get the filename out of the file path
    String filename = source.substring(source.lastIndexOf('/') + 1,source.length());

    // Create the destination path including the filename.
    if (dest.charAt(dest.length() - 1) != '/') {
      dest = dest + "/" + filename;
    } else {
      dest = dest + filename;
    }

    // System.out.println("Adding file to " + destination);

    // Check if the file already exists
    Path path = new Path(dest);
    if (fileSystem.exists(path)) {
      System.out.println("File " + dest + " already exists");
      return;
    }

    // Create a new file and write data to it.
    FSDataOutputStream out = fileSystem.create(path);
    InputStream in = new BufferedInputStream(new FileInputStream(new File(
        source)));

    byte[] b = new byte[1024];
    int numBytes = 0;
    while ((numBytes = in.read(b)) > 0) {
      out.write(b, 0, numBytes);
    }

    // Close all the file descriptors
    in.close();
    out.close();
    fileSystem.close();
  }

  /**
   * read a file from hdfs
   * @param file
   * @param conf
   * @throws IOException
   */
  public void readFile(String file, Configuration conf) throws IOException {
    FileSystem fileSystem = FileSystem.get(conf);

    Path path = new Path(file);
    if (!fileSystem.exists(path)) {
      System.out.println("File " + file + " does not exists");
      return;
    }

    FSDataInputStream in = fileSystem.open(path);

    String filename = file.substring(file.lastIndexOf('/') + 1,
        file.length());

    OutputStream out = new BufferedOutputStream(new FileOutputStream(
        new File(filename)));

    byte[] b = new byte[1024];
    int numBytes = 0;
    while ((numBytes = in.read(b)) > 0) {
      out.write(b, 0, numBytes);
    }

    in.close();
    out.close();
    fileSystem.close();
  }

  /**
   * delete a directory in hdfs
   * @param file
   * @throws IOException
   */
  public void deleteFile(String file, Configuration conf) throws IOException {
    FileSystem fileSystem = FileSystem.get(conf);

    Path path = new Path(file);
    if (!fileSystem.exists(path)) {
      System.out.println("File " + file + " does not exists");
      return;
    }

    fileSystem.delete(new Path(file), true);

    fileSystem.close();
  }

  /**
   * create directory in hdfs
   * @param dir
   * @throws IOException
   */
  public void mkdir(String dir, Configuration conf) throws IOException {
    FileSystem fileSystem = FileSystem.get(conf);

    Path path = new Path(dir);
    if (fileSystem.exists(path)) {
      System.out.println("Dir " + dir + " already not exists");
      return;
    }

    fileSystem.mkdirs(path);

    fileSystem.close();
  }

  public static void main(String[] args) throws IOException {

    if (args.length < 1) {
      System.out.println("Usage: hdfsclient add/read/delete/mkdir"
          + " [<local_path> <hdfs_path>]");
      System.exit(1);
    }

    FileSystemOperations client = new FileSystemOperations();
    String hdfsPath = "hdfs://" + args[0] + ":" + args[1];

    Configuration conf = new Configuration();
    // Providing conf files
    // conf.addResource(new Path(HDFSAPIDemo.class.getResource("/conf/core-site.xml").getFile()));
    // conf.addResource(new Path(HDFSAPIDemo.class.getResource("/conf/hdfs-site.xml").getFile()));
    // (or) using relative paths
    //    conf.addResource(new Path(
    //        "/u/hadoop-1.0.2/conf/core-site.xml"));
    //    conf.addResource(new Path(
    //        "/u/hadoop-1.0.2/conf/hdfs-site.xml"));

    //(or)
    // alternatively provide namenode host and port info
    conf.set("fs.default.name", hdfsPath);

    if (args[0].equals("add")) {
      if (args.length < 3) {
        System.out.println("Usage: hdfsclient add <local_path> "
            + "<hdfs_path>");
        System.exit(1);
      }

      client.addFile(args[1], args[2], conf);

    } else if (args[0].equals("read")) {
      if (args.length < 2) {
        System.out.println("Usage: hdfsclient read <hdfs_path>");
        System.exit(1);
      }

      client.readFile(args[1], conf);

    } else if (args[0].equals("delete")) {
      if (args.length < 2) {
        System.out.println("Usage: hdfsclient delete <hdfs_path>");
        System.exit(1);
      }

      client.deleteFile(args[1], conf);

    } else if (args[0].equals("mkdir")) {
      if (args.length < 2) {
        System.out.println("Usage: hdfsclient mkdir <hdfs_path>");
        System.exit(1);
      }

      client.mkdir(args[1], conf);

    } else {
      System.out.println("Usage: hdfsclient add/read/delete/mkdir"
          + " [<local_path> <hdfs_path>]");
      System.exit(1);
    }

    System.out.println("Done!");
  }
}

This is really helpful. I am QA new to Hadoop.Just a quick one, are the commented codes not part of the code base or is there a reason they are commented.

How does it work? How do I send a command for Hadoop(HDFS)?

this code can work? do you can run this code ? actually, this code have problem, need some change about argument.

thanks, I'm new to Hadoop and it's very helpful.
Thanks a lot

Thanks.