Generating Swagger documentation from existing Java code?

The process for generating swagger definition from existing code is simple.

Add the following dependencies (I happen to use Maven):

<dependency>
  <groupId>io.springfox</groupId>
  <artifactId>springfox-swagger2</artifactId>
  <version>2.9.2</version>
</dependency>
<dependency>
  <groupId>io.springfox</groupId>
  <artifactId>springfox-swagger-ui</artifactId>
  <version>2.9.2</version>
</dependency>

This adds a swagger-ui in your application that can be accessed with

http://<host>:<port>/swagger-ui.html

Hit the API documentation (/v2/api-docs) link and you will get a JSON file that can be easily converted to YAML file using http://editor.swagger.io (Edit -> Convert to YAML)