🚀 20+ Java Open Source Projects to Contribute To

Java continues to be one of the most in-demand programming languages across the software industry. As per GitHub’s The State of the Octoverse, Java was the third most popular language on the platform in 2020—right after JavaScript and Python. So if you’re thinking about learning Java or improving your skills, contributing to open source is a fantastic way to go.

Contributing to Open Source Java-based projects not only helps you build your portfolio but also connects you with other developers and gives real-world experience with collaborative development.

Here are 20+ awesome Java projects you can contribute to based on your experience level:

Beginner-Friendly Projects

Open Latex Studio

⭐ GitHub Stars: 150+ | 🪲 Issues: 30+

A collaborative LaTeX editor that uses cloud services like Google Drive or Dropbox. Ideal for beginners interested in Java and document editing tools.

Dropwizard Jobs

⭐ GitHub Stars: 130+ | 🪲 Issues: 18+

Integrates Quartz scheduler with Dropwizard for managing background jobs.

News Android

⭐ GitHub Stars: 500+ | 🪲 Issues: 78+

Android client for the Nextcloud News reader app. Great for learning Android and Java.

Book Project

⭐ GitHub Stars: 270+ | 🪲 Issues: 25+

Track your reading activity, classify books, and share your progress.

SeriesGuide

⭐ GitHub Stars: 1.6k+ | 🪲 Issues: 40+

Android app to track movies and TV shows.

Exercism/Java

⭐ GitHub Stars: 400+ | 🪲 Issues: 20+

Learn Java through exercises and mentorship. Contribute by improving the exercises or tests.

Intermediate-Level Projects

Teammates

⭐ GitHub Stars: 1.2k+ | 🪲 Issues: 90+

Feedback management tool used in academic institutions worldwide.

OKDownload

⭐ GitHub Stars: 4.3k+ | 🪲 Issues: 210+

A powerful, flexible file downloader for Android.

Zerocode

⭐ GitHub Stars: 500+ | 🪲 Issues: 65+

Tool for automated testing of REST, SOAP, and Kafka data streams.

Appsmith

⭐ GitHub Stars: 17.6k+ | 🪲 Issues: 2k+

Build internal tools using drag-and-drop UI. While it’s mainly TypeScript-based, there are several Java-related contributions.

LanguageTool

⭐ GitHub Stars: 6.5k+ | 🪲 Issues: 1.5k+

Grammar and spell checker supporting 20+ languages.

AntennaPod

⭐ GitHub Stars: 4.2k+ | 🪲 Issues: 200+

An easy-to-use Android podcast manager.

Baritone

⭐ GitHub Stars: 4.4k+ | 🪲 Issues: 600+

Minecraft pathfinding bot fully built in Java.

Algorithms

⭐ GitHub Stars: 12.6k+ | 🪲 Issues: 50+

A repository full of commonly used algorithms and data structures.

OpenRefine

⭐ GitHub Stars: 8.3k+ | 🪲 Issues: 600+

A tool to clean and transform messy data—perfect for data engineers.

JavaPoet

⭐ GitHub Stars: 9.6k+ | 🪲 Issues: 80+

Java API for generating .java source files automatically.

Mockito

⭐ GitHub Stars: 12k+ | 🪲 Issues: 300+

One of the most popular testing libraries for Java.

Realm Java

⭐ GitHub Stars: 11k+ | 🪲 Issues: 350+

A fast local database for Android, using object-oriented models.

Advanced-Level Projects

Guava (Google Core Libraries)

⭐ GitHub Stars: 42k+ | 🪲 Issues: 600+

Includes collections, caching, primitives, concurrency libraries, and more.

Glide

⭐ GitHub Stars: 31k+ | 🪲 Issues: 250+

Image loading and caching library for Android.

Spring Boot

⭐ GitHub Stars: 61k+ | 🪲 Issues: 500+

The most popular Java framework for building microservices.

🧵 Connect With Me

You can follow me on Twitter for more such tech content: @surajondev

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💬 Final Thoughts

Hope this list helps you find a good Java project to contribute to. Whether you're a beginner or a seasoned dev, there’s something for everyone in the open-source world.

Happy coding!