Core Java (Collection Framework, Exception Handling, Multi-threading, Java 8 features), SQL, OOP, Design Patterns, DBMS, Spring Boot, Spring (MVC, ORM, AOP, Actuator, Data JPA, Cloud), Microservices Architecture, REST APIs, JUnit, Mockito, JaCoCo, SonarQube, Swagger/OpenAPI, Scalar, Grafana, Loki, Prometheus, OpenTelemetry, ECS Logging, Gradle, Maven, GitLab, IntelliJ IDEA, VS Code, Postman, DBeaver, PostgreSQL, Cassandra, H2, Ubuntu