If you want to become a Full Stack Java developer, then you are expected the below skills
Corejava : Very strong, especially Java5, 8 and 9
BackEnd / Server Side Technologies : Java Enterprise Edition, Frameworks such as Spring, Struts, WebServices (REST and SOAP), Hibernate or JPA
Database : Basic knowledge of SQL and related topics
Application Servers : Tomcat or Weblogic or Websphere
Added advantages are knowing designing skills such as UML and Agile Working Experience and Mobile Application Development using Android SDK or Swift and familiar with Cloud Computing in order to take care of DevOps.
Familiarity with Continuous Integration and Continuous Development using tools as Jenkins, Hudson and Version Controlling Systems such as Git, Subversion is a huge plus.
Hope this will help!!