InfluxDB 3 OSS is now GA. Transform, enrich, and act on time series data directly in the database. Automate critical tasks and eliminate the need to move data externally. Download now. Learn more →
Top 23 Java open-source Projects
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Sevalla
Deploy and host your apps and databases, now with $50 credit! Sevalla is the PaaS you have been looking for! Advanced deployment pipelines, usage-based pricing, preview apps, templates, human support by developers, and much more!
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swagger-core
Examples and server integrations for generating the Swagger API Specification, which enables easy access to your REST API
To use the Swagger Annotations or Micronaut OpenAPI annotations add them to compile classpath
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Project mention: Nextcloud cries foul over Google Play Store app rejection | news.ycombinator.com | 2025-05-13
> I believe the nextcloud team when they say they need the permission.
I don't (and I do use NC). The sentence "SAF cannot be used, as it is for sharing/exposing our files to other apps" is simply wrong and llm_thread is right that SAF should be able to handle that use case,see
https://developer.android.com/training/data-storage/shared/d...
There are some restrictions regarding which directories you can access, but for most use-cases it should be perfectly fine. It's also not that this should come as a surprise to them. In fact, there's an issue about this from the NC team themselves from August '23:
https://github.com/nextcloud/android/issues/10123
Why they still think SAF cannot be used is a mystery to me.
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Shelter
A Free and Open-Source (FOSS) app that leverages the "Work Profile" feature of Android to provide an isolated space that you can install or clone apps into.
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OpenBoard
100% foss keyboard based on AOSP, with no dependency on Google binaries, that respects your privacy.
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InfluxDB
InfluxDB – Built for High-Performance Time Series Workloads. InfluxDB 3 OSS is now GA. Transform, enrich, and act on time series data directly in the database. Automate critical tasks and eliminate the need to move data externally. Download now.
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soapui
SoapUI is a free and open source cross-platform functional testing solution for APIs and web services.
Project mention: Diving into Spring Web Services (Spring-WS): Contract-First SOAP Service Development | dev.to | 2025-04-15Contract Testing: Implement contract tests (e.g., using SoapUI or Spring Cloud Contract) to ensure your service stays compliant with the defined contract.
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Project mention: A web extension to redirects YouTube, X, etc. to privacy-friendly front ends | news.ycombinator.com | 2025-06-21
I just found out about an Android app where you can set up custom redirects for any links, OS-wide: https://github.com/TrianguloY/URLCheck
It's a little finnicky to set up, but I'm enjoying it so far. It goes beyond alternative frontend redirects. You can strip URL params, check domains against a blacklist, and choose native apps to open links that match a pattern.
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linstor-server
High Performance Software-Defined Block Storage for container, cloud and virtualisation. Fully integrated with Docker, Kubernetes, Openstack, Proxmox etc.
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Slimefun4
Slimefun 4 - A unique Spigot/Paper plugin that looks and feels like a modpack. We've been giving you backpacks, jetpacks, reactors and much more since 2013.
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DSpace
(Official) The DSpace digital asset management system that powers your Institutional Repository
Dublin Core is the main metadata schema for many institutional repositories, for example the DSpace platform https://github.com/DSpace/dspace. The schema essentially only covers basic bibliographic metadata and has a strong pre-digital library feel to it. We end up augmenting with other custom schemas to be able to describe content in our repository, for example podcasts and journal articles with different issue and online dates, as well as extra metadata like author affiliations, funders, internal programs etc.
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Openkoda positions itself as the “own-the-code” alternative to heavyweight suites for insurance industry.
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valkey-glide
An open source Valkey client library that supports Valkey, and Redis open source 6.2, 7.0 and 7.2. Valkey GLIDE is designed for reliability, optimized performance, and high-availability, for Valkey and Redis OSS based applications. GLIDE is a multi language client library, written in Rust with programming language bindings, such as Java and Python
Project mention: Redis is trying to take over the all of the OSS Redis libraries | news.ycombinator.com | 2024-11-25 -
Project mention: I wasted weeks hand optimizing assembly because I benchmarked on random data | news.ycombinator.com | 2025-07-24
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steady
Analyses your Java applications for open-source dependencies with known vulnerabilities, using both static analysis and testing to determine code context and usage for greater accuracy. https://eclipse.github.io/steady/
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
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).
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A note from our sponsor - InfluxDB
www.influxdata.com | 1 Sep 2025
Index
What are some of the best open-source open-source projects in Java? This list will help you:
| # | Project | Stars |
|---|---|---|
| 1 | cas | 11,183 |
| 2 | swagger-core | 7,449 |
| 3 | android | 4,816 |
| 4 | Shelter | 2,949 |
| 5 | Omni-Notes | 2,762 |
| 6 | OpenBoard | 2,681 |
| 7 | audiveris | 2,059 |
| 8 | android-demos | 1,995 |
| 9 | soapui | 1,639 |
| 10 | URLCheck | 1,540 |
| 11 | linstor-server | 1,123 |
| 12 | Slimefun4 | 1,053 |
| 13 | DSpace | 997 |
| 14 | openkoda | 983 |
| 15 | personalDNSfilter | 771 |
| 16 | knime-core | 732 |
| 17 | News-Android-App | 728 |
| 18 | X-Road | 709 |
| 19 | countly-sdk-android | 698 |
| 20 | ContentBlocker | 637 |
| 21 | valkey-glide | 566 |
| 22 | SAP Machine | 559 |
| 23 | steady | 541 |
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