For a full stack Java developer you should start with learning backend and front-end technologies
From the backend perspective:
- Java, multithreading, collections, jdbc, etc.
- Spring framework
- Hibernate
- Get good hold of SQL. You can use mysql.
- Learn the how to deploy web servers Apache, database servers and configure them.
- Learn to use Nix based open source systems (ubuntu or community enterprise systems like centos). User management, firewall management, ssh, etc.
From the Front-end perspective:
- Start learning Html, css, JavaScript
- Try to understand how browsers work and to debug front-end in browsers.
- Learn about responsive UI and a UI framework like bootstrapjs.
- Learn JavaScript mvc framework like Angularjs.
Learn design patterns and basics of networking.
Never give up and never give a f**k!