The simplest way is to integrate a Java application with ADUCID. It is based on Java SDK Client API. It implements all necessary calls directly to your application returning authentication (operation) result into your session variables. Ideal when you are starting a new project
The architecture of Web Platform is provided in the picture below:
Follow steps described in provided Javadoc documentation api-web-[version]-javadoc.jar. See also api-web-webapp-[version].war demo application as the real example of Web Platform integration.