How to open Java website API for third party developers?

Question

Java

The goal is for site users to develop and upload their own widgets and other site components to the server for others to use.
Website in Java. Tomcat server.

Answer 1

In order for someone to develop something using your product's API, you need to prepare an SDK (software development kit) for developers, with detailed documentation on your SDK's API. As an example, you can look at the Atlassian SDK, which allows you to write modules, plugins for Atlassian products (JIRA, Bamboo, Crucible, etc.)
This is not a very easy thing, I'll tell you... Go for it!