Top 12 Java Open Source Projects on GitHub You Should Explore in 2025

Imagine you’re a cricketer, starting with basic shots like a straight drive. As you evolve, you start adding your style, making each shot more confident and unique. Over time, it becomes your signature move. That’s what contributing to Java open-source projects on GitHub is like. You begin with existing code, but each change you make adds your touch, helping you grow and develop your skills along the way.

Working on Java projects is valuable, but contributing to open-source on GitHub can boost your chances of landing a job by up to 10 times. Every pull request or bug fix can hone your skills and also enhance your resume. Curious about how Java projects on GitHub work?

Dive into this blog to explore the top 12 open-source Java projects on GitHub that you can explore and learn from! 

Java Projects for Beginners on GitHub

If you’re a new learner, you must gain hands-on experience before exploring a career in Java programming. The following open-source Java projects on GitHub are designed to help new developers understand core Java concepts and prepare them for more advanced programming challenges.

Here are the top Java open source projects GitHub for beginners.

1. The Corona-Warn-App

The Corona-warn app is a public health application that can track and trace COVID-19 exposure. The app uses Bluetooth and anonymous data collection to notify users if they have come in contact with a person with an infection.

Key Features:

• User-friendly notifications
• Contact tracing using decentralized technology
• Integration with government data repository

Skills Gained:

• Integrating APIs for real-time updates
• Data privacy and anonymization techniques
• Using Bluetooth for communication

Tools and Technology:

• Android Studio for building Android application
• Firebase database for notifications and data storage
• Gradle for managing dependencies

Applications:

• Health monitoring apps
• Public health and safety applications

Also Read: Firebase Vs. MongoDB

2. Elasticsearch

Elasticsearch is a search and analytics engine used for full-text search, logging, and data analytics. As a part of the ELK (Elasticsearch, Logstash, Kibana) stack, Elasticsearch is used to index, search, and analyze large volumes of data.

Key Features:

• Real-time indexing and querying of large data sets
• Full-text search 
• Distributed search and analytics capabilities

Skills Gained:

• Implementing search functionality in web apps
• Real-time data processing
• Understanding Big Data 

Tools and Technology:

• Maven dependency management tool
• Kibana data visualization tool
• Elasticsearch for search and analytics engine 

Applications:

• Real-time search applications
• Logging and monitoring systems
• Data-driven analytics

Also Read: How to Create Maven Projects?

3. OkHttp

OkHttp is an efficient HTTP client for Android and Java applications. The tool allows easy handling of network requests, including HTTP/HTTPS connections, WebSocket communication, and APIs. 

Key Features:

• Supports HTTP/2 and WebSocket protocols
• Easy integration with Rest APIs and JSON parsing
• Secure and efficient network calls

Skills Gained:

• Parsing JSON data from APIs
• Optimizing network performance
• Understanding HTTP protocols

Tools and Technology:

• OkHttp network library for making HTTP requests
• Gradle dependency management tool
• Retrofit library for easier API integration

Applications:

• API communication for mobile apps
• Social media apps with real updates
• E-commerce platforms with payment gateways

4. RxJava

RxJava is a reactive programming Java library that makes it easier to work with asynchronous data streams. 

Key Features:

• Can handle asynchronous programming
• Easy integration with Android for reactive UI updates
• Supports chaining of events and callbacks

Skills Gained:

• Managing asynchronous operations 
• Implementing functional programming patterns in Java
• Working with reactive programming

Tools and Technology:

• RxJava library for reactive programming
• Android Studio to build Android applications
• Gradle dependency management tool

Applications:

• Asynchronous data handling in mobile apps
• Real-time applications like sports

5. Glide

Glide is a library used for Android image loading and caching. Glide helps you load images efficiently and cache them for better performance.

Key Features:

• Efficient image loading and caching
• Supports GIF and animated images
• Optimized for smooth scrolling 

Skills Gained:

• Working with image formats like JPEG and GIF
• Integrating libraries with Android UI components
• Handling image loading caching in apps

Tools and Technology:

• Glide library for image loading and caching
• Maven dependency management tool
• GitHub for version control

Applications:

• Image-heavy mobile applications like social media
• Smooth scrolling apps like News.
• Product images on e-commerce apps

Did you know Java programming can unlock new job opportunities? Enrol in upGrad’s free course on Java Object-Oriented Programming to master the fundamentals.

Having explored a selection of introductory Java projects on GitHub, you can turn your attention to projects suitable for intermediate learners.

Java Projects for Intermediate Developers on GitHub

If you’re an intermediate Java developer looking to take your skills to the next level, working on real-world Java projects on GitHub is a great way to advance your knowledge. 
These projects help you refine your coding abilities, understand best programming practices, and expose you to industry-standard tools and libraries.

Here are the best Java projects on GitHub.

6. MPAndroidChart

MPAndroidChart is an open-source Android charting library that allows you to create visually appealing, interactive charts for your apps. 

Key Features:

• Supports charts such as line, pie, and scatter
• Customizable chart styling
• Support touch gestures

Skills Gained:

• Working with Android Views
• Data visualization techniques
• Building interactive UIs

Tools and Technology:

• Android studio for building Android apps
• XML for layout design
• MPAndroidChart library for creating charts

Applications:

• Data visualization for stock price tracking
• Health and fitness apps 
• Educational apps to display statistics and results

Also Read: HTML Vs XML: Difference Between HTML and XML

7. Lottie

Lottie is an open-source library for executing animations in Android, iOS, and the web. Lottie uses JSON data exported from Adobe After Effects to carry out smooth, scalable animations.

Key Features:

• Supports vector-based animations
• Easy to use with minimal setup
• Compatible with iOS, Android, and web applications

Skills Gained:

• Working with JSON data
• Optimizing animation performance
• Creating smooth animations for mobile and web applications

Tools and Technology:

• Lottie Library for animation
• After Effects for creating animations
• GitHub for version control

Applications:

• Mobile apps with custom animations 
• Marketing apps for creating engaging user interface
• E-commerce apps for interactive product displays

Also Read: An Introduction to Package JSON Scripts in Node.js

8. EventBus

EventBus is a tool that makes it easier to send messages between different parts of your Android app without them needing to know about each other directly. This helps to keep your app organized and easier to maintain.

Key Features:

• Supports event delivery to subscriber methods
• Easy to implement with minimal boilerplate code
• Strong typing and compile-time checks to avoid errors

Skills Gained:

• Implementing event-driven programming models
• Optimizing communication between app components
• Managing thread safety in event-driven communication

Tools and Technology:

• Android Studio for Android app development
• Gradle dependency management tool for Android projects
• EventBus for event-based communication

Applications:

• Real-time updates for live data apps
• Messaging and notification system within the app
• Communication between services

Also Read: How to Code, Compile and Run Java Projects?

Completed intermediate-level Java projects on GitHub? Explore these advanced projects that will challenge and deepen your Java expertise.

Java Projects for Advanced Developers on GitHub

If you are a Java developer looking for challenging projects, these GitHub projects are just for you. These projects will help you refine your coding skills and introduce you to best practices in Java development.

Here’s a list of Java open source projects GitHub for advanced learners.

9. Mockito

Mockito is a mocking framework that allows you to create mock objects for unit testing. Mockito can isolate classes and components to test them independently, ensuring an efficient way of writing unit tests for complex systems.

Key Features:

• Works with JUnit and other testing frameworks
• Easy creation of mock objects 
• Stubbing methods to return predefined results

Skills Gained:

• Verifying method calls and interactions in tests
• Writing maintainable and scalable test suites 
• Implementing test-driven development (TDD)

Tools and Technology:

• Maven to build automation tools for managing dependencies
• for creating mock objects in tests
• JUnit for unit testing

Applications:

• Unit testing in Java applications
• Integration testing of large-scale Java systems
• Testing multi-component applications

10. Java-Design-Patterns

Java-design-patterns is a repository of design patterns implemented in Java. It covers all classic design patterns and demonstrates their usage in real-world scenarios. 

Key Features:

• Collection of more than 20 design patterns in Java
• Shows the practical application of design patterns
• Facilitates code reusability, scalability, and maintainability

Skills Gained:

• A clear understanding of design patterns 
• Improving software architecture
• Improving code readability 

Tools and Technology:

• JUnit for testing
• UML for creating design diagrams for patterns
• GitHub for version control

Applications:

• Implementing reusable components 
• Developing scalable enterprise-level applications

Also Read: Design Patterns: Singleton in Java

11. Spring Boot

Spring Boot is a Java framework that is used to build production-ready applications. Spring Boot is used to build web and enterprise applications by providing production-ready features like security, logging, and metrics.

Key Features:

• Integrated development and testing support
• Easy integration with databases
• Auto-configurations for various components like security messaging.

Skills Gained:

• Implementing RESTful APIs with Spring Boot
• Managing databases and transactions using Spring Data
• Building full-fledged web applications

Tools and Technology:

• Spring Data JPA for database interaction
• GitHub for version control
• Gradle for managing dependencies

Applications:

• Building RESTful APIs for web applications
• Full-stack web applications

Also Read: What is Full Stack Developer & What are the Most Demanded FSD Skills?

12. Guava

Guava is a Google-developed library that makes Java programming easier. It helps with common tasks like storing data, working with collections, and writing cleaner code. This saves developers time and effort.

Key Features:

• A caching library for local caching in applications
• Powerful utility classes for string manipulation
• Easy integration with other libraries and frameworks

Skills Gained:

• Using functional programming patterns in Java
• Implementing efficient caching solutions in Java applications
• Working with advanced data structures and algorithms

Tools and Technology:

• Guava library to enhance Java functionality 
• Gradle to manage dependencies
• JUnit to validate code functionality 

Applications:

• Performance optimization in Java applications 
• Large-scale data handling and manipulation
• Building scalable, high-performance backend services

Also Read: 22 Best Java Project Ideas & Topics For Beginners With Source Code 2024

Now that you’ve covered an overview of Java projects on GitHub, let’s explore how to choose the right project for you.

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How to Choose the Right Java Project on GitHub

As a Java developer, the right Java project can help you contribute to GitHub and can significantly impact your learning and career development. Before choosing a project, consider factors like project size, activity level, and how well the project aligns with your skills and interests.

Here are some factors you must consider before choosing a Java project on GitHub.

• Assess your skill level

If you’re a beginner, choose a project that focuses on fundamental concepts like basic Java syntax. If you’re an advanced learner, focus on enterprise-level solutions or specialized areas like Big data or machine learning.

• Check the size of the project

Smaller projects are good for beginners wanting to practice specific Java features. Large and complex projects are a great way to learn new skills if you’re an advanced-level learner.

• Evaluate community involvement

Projects having an active and supportive community will provide you with the required guidance and help with any issues you face. Projects with contributing guidelines are an indication of organized projects.

• Project activity

Check if the project has recent commits to verify it's active. A project without an update may be abandoned or lacks long-term support. Checking the project discussion forum is the best way to analyze a project’s health.

• Project readability

Check projects with a well-written README document. A project with setup instructions and an overview can help you learn and contribute effectively.

• Alignment between the project’s objectives and your goals

Choose a project that focuses on the areas you want to grow, whether it’s backend web development, mobile apps, or cloud integration. The correct project will give you hands-on experience and help you develop in the desired areas.

• Career alignment

If you have a specific career in mind, choose a project that focuses on the field. Contributing to these projects can help you build a portfolio and showcase your expertise to potential employers.

• Evaluate project tool requirements

Check the libraries and tools needed for the project. If the project requires new technology, it’s an opportunity to learn new tools while contributing. 

Now that you're familiar with the factors to consider when choosing a project, let's explore the common challenges you may face when contributing to Java projects on GitHub.

Common Challenges in Contributing to Java Projects on GitHub

Contributing to open-source Java projects on GitHub has its advantages, but it also comes with its unique challenges. Problems such as undertaking large code bases can affect your ability to learn and implement the project.

Here are some common challenges you may face while contributing to Java projects on GitHub.

• Understanding large code bases

In large projects, understanding how different modules interact, finding areas to contribute, and learning the project’s structure can be challenging. As a beginner, this is often the biggest hurdle when exploring projects on GitHub.

• Understanding documentation 

Unclear documentation is one of the most common obstacles you may face when contributing to open-source projects. Without clear guidelines, you can find it difficult to know where to begin or how to follow the project’s workflow.

• Handling merge conflicts

When the changes you’ve made conflict with those made by other contributors, it leads to merge conflicts. For a new learner, merge conflicts can affect your learning process. 

• Communicating with other developers

While working on the same section of the code, you may face conflict with other developers. Communicating with them to resolve the issues is a challenging aspect of the contributing process.

• Code review process

If you’re new to open-source contributions, you may receive critical or detailed comments, which can be intimidating. It is necessary to take the feedback constructively. 

• Finding the right problems to solve

It can be difficult to find the right issue to work on. You may come across tasks that are too complex or beyond your current skill level. 

Here are some practical advice to overcome the challenges.

• Start with small problems

Begin your contributing process with small issues or bug fixes that don’t require extensive knowledge of the entire codebase.

• Learn the workflow

Understand the contributing guidelines of the project, including how to fork, clone, and create pull requests.

• Stay updated

Regularly sync your local branch with the main repository to avoid falling behind.

• Ask for suggestions

Don’t hesitate to reach out to the maintainers or the community if you're stuck on any project. 

• Build confidence

Contributing to open-source takes lots of practice. With each contribution, you’ll become more comfortable with the process and the codebase.

You might be wondering about the career opportunities that follow contributing to Java projects on GitHub. Check the subsequent section for details.

How Can upGrad Help You Improve Your Java Skills and Contribute to Open Source Projects?

Exploring and contributing to Java projects on GitHub can sharpen your programming skills, gain hands-on experience, and build a strong portfolio. With the tech field constantly evolving, you’d require regular upskilling to position yourself for success in the competitive job market.

To help you stay on top of your game, upGrad offers comprehensive courses in Java programming, where you can gain hands-on experience and learn from industry experts.

Here are some of the top courses offered by upGrad in Java programming.

• Java Object-Oriented Programming
• Core Java Basics

Do you need help deciding which course to take to advance your career in Java programming? Contact upGrad for personalized counseling, or visit your nearest upGrad Career Centre to start accelerating your future!

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Project Source Code:

1. The Corona-Warn-App Project Source Code  
2. Elasticsearch Project Source Code
3. OkHttp Project Source Code
4. RxJava Project Source Code
5. Glide Project Source Code
6. MPAndroidChart Project Source Code
7. Lottie Project Source Code
8. EventBus Project Source Code
9. Mockito Project Source Code
10. Java-Design-Patterns Project Source Code
11. Spring Boot Project Source Code
12. Guava Project Source Code