1. Java Core (OOP, Stream API, IO, Multithreading, Reflection) 2. Java GUI's (AWT, Swing) 3. Data Bases (SQL, ORM, JPA, Hibernate, HQL, JPQL, JTA, PostgreSQL, MySQL) 4. Java EE (HTTP, Sockets, ReST, Servlets, Filters, JSP, JSTL, EL, Velocity, FreeMarker, Git, XML, Maven, JUnit, Mockito, Slf4j, Tomcat, Jetty) 5. Spring Ecosystem (Spring DI, SPeL, Spring AOP, Spring JDBC, Spring ORM, Spring Data JPA, Spring MVC, Spring Security, Spring Integration, Spring Boot, Spring Web Flow) 6. Frontend (HTML 5, CSS 3, JS Basic)