DZone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
Refcards Trend Reports
Events Video Library
Refcards
Trend Reports

Events

View Events Video Library

Zones

Culture and Methodologies Agile Career Development Methodologies Team Management
Data Engineering AI/ML Big Data Data Databases IoT
Software Design and Architecture Cloud Architecture Containers Integration Microservices Performance Security
Coding Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
Culture and Methodologies
Agile Career Development Methodologies Team Management
Data Engineering
AI/ML Big Data Data Databases IoT
Software Design and Architecture
Cloud Architecture Containers Integration Microservices Performance Security
Coding
Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance
Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks

Generative AI has transformed nearly every industry. How can you leverage GenAI to improve your productivity and efficiency?

SBOMs are essential to circumventing software supply chain attacks, and they provide visibility into various software components.

Related

  • Redis-Based Tomcat Session Management
  • Migrate HDFS Data to Azure
  • Your First Java RDD With Apache Spark
  • Modernizing Apache Spark Applications With GenAI: Migrating From Java to Scala

Trending

  • Lessons Learned in Test-Driven Development
  • Exploring Data Redaction Enhancements in Oracle Database 23ai
  • Indexed Views in SQL Server: A Production DBA's Complete Guide
  • Multiple Stakeholder Management in Software Engineering
  1. DZone
  2. Data Engineering
  3. Big Data
  4. Simple Java Program to Append to a File in HDFS

Simple Java Program to Append to a File in HDFS

Get the code and instructions needed to build a Java program to append to a file in HDFS, using Maven as the build tool.

By 
Simarpreet Kaur Monga user avatar
Simarpreet Kaur Monga
·
Feb. 23, 18 · Tutorial
Likes (4)
Comment
Save
Tweet
Share
17.8K Views

Join the DZone community and get the full member experience.

Join For Free

In this article, I will present you with a Java program to append to a file in HDFS.

I will be using Maven as the build tool.

First, we need to add Maven dependencies in the pom.xml.

Now, we need to import the following classes:

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.*;

We will be using the hadoop.conf.Configuration class to set the file system configurations as per the configuration of the Hadoop cluster installed.

Let's now start with configuring the file system:

public FileSystem configureFileSystem(String coreSitePath, String hdfsSitePath) {
    FileSystem fileSystem = null;
    try {
        Configuration conf = new Configuration();
        conf.setBoolean("dfs.support.append", true);
        Path coreSite = new Path(coreSitePath);
        Path hdfsSite = new Path(hdfsSitePath);
        conf.addResource(coreSite);
        conf.addResource(hdfsSite);
        fileSystem = FileSystem.get(conf);
    } catch (IOException ex) {
        System.out.println("Error occurred while configuring FileSystem");
    }
    return fileSystem;
}

Make sure that the property dfs.support.append in hdfs-site.xml is set to true.

You can either set it manually by editing the hdfs-site.xml file or programmatically using:

conf.setBoolean("dfs.support.append", true);

Now that the file system is configured, we can access the files stored in HDFS.

Let's start with appending to a file in HDFS.

public String appendToFile(FileSystem fileSystem, String content, String dest) throws IOException {

    Path destPath = new Path(dest);
    if (!fileSystem.exists(destPath)) {
        System.err.println("File doesn't exist");
        return "Failure";
    }

    Boolean isAppendable = Boolean.valueOf(fileSystem.getConf().get("dfs.support.append"));

    if(isAppendable) {
        FSDataOutputStream fs_append = fileSystem.append(destPath);
        PrintWriter writer = new PrintWriter(fs_append);
        writer.append(content);
        writer.flush();
        fs_append.hflush();
        writer.close();
        fs_append.close();
        return "Success";
    }
    else {
        System.err.println("Please set the dfs.support.append property to true");
        return "Failure";
    }
}

To see whether the data has been correctly written to HDFS, let's write a method to read from HDFS and return the content as a String.

public String readFromHdfs(FileSystem fileSystem, String hdfsFilePath) {
    Path hdfsPath = new Path(hdfsFilePath);
    StringBuilder fileContent = new StringBuilder("");
    try{
        BufferedReader bfr=new BufferedReader(new InputStreamReader(fileSystem.open(hdfsPath)));
        String str;
        while ((str = bfr.readLine()) != null) {
            fileContent.append(str+"\n");
        }
    }
    catch (IOException ex){
        System.out.println("----------Could not read from HDFS---------\n");
    }
    return fileContent.toString();
}

After that, we have successfully written and read the file in HDFS. It's time to close the file system.

public void closeFileSystem(FileSystem fileSystem){
    try {
        fileSystem.close();
    }
    catch (IOException ex){
        System.out.println("----------Could not close the FileSystem----------");
    }
}

Before executing the code, you should have Hadoop running on your system.

You just need to go to HADOOP_HOME and run following command:

./sbin/start-all.sh

For the complete program, refer to my GitHub repository.

Happy coding!

File system hadoop Java (programming language)

Published at DZone with permission of Simarpreet Kaur Monga, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

Related

  • Redis-Based Tomcat Session Management
  • Migrate HDFS Data to Azure
  • Your First Java RDD With Apache Spark
  • Modernizing Apache Spark Applications With GenAI: Migrating From Java to Scala

Partner Resources

×

Comments

The likes didn't load as expected. Please refresh the page and try again.

ABOUT US

  • About DZone
  • Support and feedback
  • Community research
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • Become a Contributor
  • Core Program
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 3343 Perimeter Hill Drive
  • Suite 100
  • Nashville, TN 37211
  • [email protected]

Let's be friends: