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Top 23 Java REST-API Projects
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openapi-generator
OpenAPI Generator allows generation of API client libraries (SDK generation), server stubs, documentation and configuration automatically given an OpenAPI Spec (v2, v3)
It would be great if D supported something like OpenAPI generator https://github.com/OpenAPITools/openapi-generator
Maybe it exists and I am just ignorant but it doesn't seem to be in the list of supported languages.
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CodeRabbit
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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: Energy-Efficient Schema-Driven Development with Spring WebMVC/WebFlux | dev.to | 2025-04-20
In Spring WebMVC/WebFlux, you can use springdoc-openapi to automatically generate an OpenAPI schema from Spring controller implementations. Having an OpenAPI schema enables automatic generation of HTML documentation and client code, which already provides some value.
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linkis
Apache Linkis builds a computation middleware layer to facilitate connection, governance and orchestration between the upper applications and the underlying data engines.
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InfluxDB
InfluxDB high-performance time series database. Collect, organize, and act on massive volumes of high-resolution data to power real-time intelligent systems.
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Solon
🔥 Java enterprise application development framework for full scenario: Restrained, Efficient, Open, Ecologicalll!!! 700% higher concurrency 50% memory savings Startup is 10 times faster. Packing 90% smaller; Compatible with java8 ~ java24. (Replaceable spring)
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spring-boot-vuejs
Example project showing how to build a Spring Boot App providing a GUI with Vue.js
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Discord4J
Discord4J is a fast, powerful, unopinionated, reactive library to enable quick and easy development of Discord bots for Java, Kotlin, and other JVM languages using the official Discord Bot API.
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serverless-java-container
A Java wrapper to run Spring, Spring Boot, Jersey, and other apps inside AWS Lambda.
Quick Start Guide: Spring Boot 3
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cats
CATS is a REST API Fuzzer and negative testing tool for OpenAPI endpoints. CATS automatically generates, runs and reports tests with minimum configuration and no coding effort. Tests are self-healing and do not require maintenance. (by Endava)
An API fuzzer I've been building for several years now: https://github.com/Endava/cats
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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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restheart
Virtual Threads Powered API Framework with ✅ Instant REST, GraphQL and Websockets APIs for MongoDB and ✅ Declarative SecurityMongoDB
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Para
Multitenant backend server for building web and mobile apps rapidly. The backend for busy developers. (self-hosted or hosted) (by Erudika)
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Project mention: Reverse engineer Spring Web in 5 minutes using a recording debugger | dev.to | 2024-12-17
We will see how the tool works on Spring Web based app. The project which we are going to use is spring-petclinic. This is a basic web app written on Java with Spring Web. Suppose, we want to understand how it works. And we want to do it really quick.
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OpenDJ - Open Identity Plattform Edition
OpenDJ is an LDAPv3 compliant directory service, which has been developed for the Java platform, providing a high performance, highly available, and secure store for the identities managed by your organization. Its easy installation process, combined with the power of the Java platform makes OpenDJ the simplest, fastest directory to deploy and manage.
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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).
Java REST-API discussion
Java REST-API related posts
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New AI tool I tested: Coderabbit and Junie
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Generate JAVA code from OpenAPI specification
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openapi-generator VS lapidary-render - a user suggested alternative
2 projects | 16 Mar 2025 -
Define, Generate, and Implement: An API-First Approach with OpenAPI Generator and FlightPHP
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OpenAPI + Swagger UI with Micronaut Application
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After 3 Years, I Failed. Here's All My Startup's Code
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OpenAPI Generator: Generate clients, servers from OpenAPI 2.0/3.x documents
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A note from our sponsor - CodeRabbit
coderabbit.ai | 26 Apr 2025
Index
What are some of the best open-source REST-API projects in Java? This list will help you:
| # | Project | Stars |
|---|---|---|
| 1 | openapi-generator | 23,505 |
| 2 | swagger-core | 7,423 |
| 3 | REST Assured | 6,959 |
| 4 | CompreFace | 6,268 |
| 5 | JDA | 4,469 |
| 6 | springdoc-openapi | 3,417 |
| 7 | linkis | 3,353 |
| 8 | Solon | 2,480 |
| 9 | schema-registry | 2,291 |
| 10 | spring-boot-vuejs | 2,103 |
| 11 | Discord4J | 1,825 |
| 12 | elassandra | 1,714 |
| 13 | serverless-java-container | 1,516 |
| 14 | cats | 1,255 |
| 15 | DSpace | 955 |
| 16 | restheart | 825 |
| 17 | Javacord | 771 |
| 18 | rsql-parser | 753 |
| 19 | Restlet Framework | 656 |
| 20 | Para | 537 |
| 21 | spring-petclinic-rest | 518 |
| 22 | DeepfakeHTTP | 515 |
| 23 | OpenDJ - Open Identity Plattform Edition | 398 |
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