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Top 23 Java Open-Source Projects
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SaaSHub
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Spring Boot
Spring Boot helps you to create Spring-powered, production-grade applications and services with absolute minimum fuss.
In this tutorial, I'll walk you through how I moved beyond basic logging by instrumenting a Kotlin and Spring Boot backend service with OpenTelemetry. You'll learn how OpenTelemetry's tracing model gives you the execution context that logs alone can't provide. By the end of this guide, you'll have a working instrumented service and a clear mental model for building more observable backend systems.
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Project mention: Amazon is discontinuing Kindle for PC on June 30th | news.ycombinator.com | 2026-04-18
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advanced-java
😮 Core Interview Questions & Answers For Experienced Java(Backend) Developers | 互联网 Java 工程师进阶知识完全扫盲：涵盖高并发、分布式、高可用、微服务、海量数据处理等领域知识
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Elasticsearch: Distributed, and analytics search engine, scalable data store, vector database focused on speed, production-ready, and scalability support. RAGFlow component, used as its default vector database, while testing, and improving Infinity. Can be used in production environments through Elastic Cloud or configured manually in the cloud platform of choice. A Docker image is available to use it locally.
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leetcode-master
《代码随想录》LeetCode 刷题攻略：200道经典题目刷题顺序，共60w字的详细图解，视频难点剖析，50余张思维导图，支持C++，Java，Python，Go，JavaScript等多语言版本，从此算法学习不再迷茫！🔥🔥 来看看，你会发现相见恨晚！🚀
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leetcode
LeetCode Solutions: A Record of My Problem Solving Journey.( leetcode题解，记录自己的leetcode解题之路。) (by azl397985856)
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Project mention: Are you really wasting your time in Java without these 10 libraries? | dev.to | 2025-11-20
Apache Commons Lang and Google Guava play the same role in the ecosystem, even though the former predates the latter: fill in the gaps in the Java standard APIs. For example, one of the biggest current PITAs in modern Java is checked exceptions inside lambdas. Both libraries provide wrapping methods to handle this specific use case. In general, modern Java versions and Kotlin drastically diminish the need for these additional dependencies.
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Project mention: CLI to manage your SQL database schemas and migrations | news.ycombinator.com | 2025-11-01
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RxJava
RxJava – Reactive Extensions for the JVM – a library for composing asynchronous and event-based programs using observable sequences for the Java VM.
RxJava Documentation
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Retrofit ProGuard Rules
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Feature transformations should be deterministic: The same input should produce the same output when the same feature definition and configuration are applied. This is what allows training, backtesting, and live inference to remain aligned. Tools such as Pandas, Spark, or feature platforms such as Feast can be used to implement that logic.
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appsmith
Platform to build admin panels, internal tools, and dashboards. Integrates with 25+ databases and any API.
AppSmith
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MPAndroidChart
A powerful 🚀 Android chart view / graph view library, supporting line- bar- pie- radar- bubble- and candlestick charts as well as scaling, panning and animations.
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Project mention: Top 7 Puppeteer Alternatives for Web Automation and Testing (2025) | dev.to | 2025-08-05
Selenium is one of the most popular and mature automated testing frameworks for web applications. Unlike Puppeteer, which is limited to Chromium, Selenium supports all major browsers—including Chrome, Firefox, Safari, and Edge—making it a reliable choice for Cross-platform browser testing.
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NOTE:
The open source projects on this list are ordered by number of github stars.
The number of mentions indicates repo mentiontions in the last 12 Months or
since we started tracking (Dec 2020).
Java discussion
Java related posts
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Mindustry
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Nuts – pip/NPM for Java with first-class workspaces and JDK provisioning (9y+)
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H2JVM – A Haskell Library for Writing JVM Bytecode
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OxyJen v0.5: a deterministic graph runtime for AI workflows
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OpenAPI, ORM, SVG and Lottie
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AI, OAuth, And Other Platform APIs In The Core
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On-Device Debugging And JUnit 5
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A note from our sponsor - SaaSHub
www.saashub.com | 12 Jun 2026
Index
What are some of the best open-source Java projects? This list will help you:
| # | Project | Stars |
|---|---|---|
| 1 | JavaGuide | 156,282 |
| 2 | Design Patterns | 94,105 |
| 3 | Spring Boot | 80,798 |
| 4 | Stirling-PDF | 80,668 |
| 5 | advanced-java | 78,986 |
| 6 | Elasticsearch | 76,940 |
| 7 | Java | 65,792 |
| 8 | interviews | 64,936 |
| 9 | leetcode-master | 61,617 |
| 10 | leetcode | 55,758 |
| 11 | Guava | 51,480 |
| 12 | dbeaver | 50,419 |
| 13 | jadx | 48,909 |
| 14 | RxJava | 48,239 |
| 15 | OkHttp | 46,971 |
| 16 | Retrofit | 43,895 |
| 17 | Apache Spark | 43,440 |
| 18 | Dubbo | 41,516 |
| 19 | appsmith | 39,980 |
| 20 | MPAndroidChart | 38,201 |
| 21 | Arthas | 37,359 |
| 22 | Selenium WebDriver | 34,156 |
| 23 | spring-boot-demo | 34,106 |
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