What skills you need to become a full stack java developer?

For a full stack Java developer you should start with learning backend and front-end technologies

From the backend perspective:

1. Java, multithreading, collections, jdbc, etc.
2. Spring framework
3. Hibernate
4. Get good hold of SQL. You can use mysql.
5. Learn the how to deploy web servers Apache, database servers and configure them.
6. 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:

1. Start learning Html, css, JavaScript
2. Try to understand how browsers work and to debug front-end in browsers.
3. Learn about responsive UI and a UI framework like bootstrapjs.
4. Learn JavaScript mvc framework like Angularjs.

Learn design patterns and basics of networking.

Never give up and never give a f**k!