How to generate OpenAPI 3.0 YAML file from existing Spring REST API?

We have used lately springdoc-openapi java library. It helps automating the generation of API documentation using spring boot projects.

It automatically deploys swagger-ui to a spring-boot application Documentation will be available in HTML format, using the official [swagger-ui jars]:

The Swagger UI page should then be available at http://server:port/context-path/swagger-ui.html and the OpenAPI description will be available at the following url for json format: http://server:port/context-path/v3/api-docs

• server: The server name or IP
• port: The server port
• context-path: The context path of the application

Documentation can be available in yaml format as well, on the following path: /v3/api-docs.yml. Add the library to the list of your project dependencies (No additional configuration is needed)

 <dependency>
      <groupId>org.springdoc</groupId>
      <artifactId>springdoc-openapi-ui</artifactId>
      <version>1.2.3</version>
  </dependency>

I was missing some library for this for longer time. Finally, decided to implement my own generator https://github.com/jrcodeza/spring-openapi maybe you can check it out too. It's based on reflection and supports javax and spring annotations. It also generates inheritance model (with discriminators) based on Jackson annotations. Besides you can define your own interceptors if you want to alter generation process (e.g. when you have your own annotations and need to adjust generated sections of schema). You can use it in runtime mode or as a maven plugin. There is also OpenAPI3 to java client generator, which generates the model. Again it generates also Javax annotations and Jackson annotations for correct inheritance.