1. Java Fundamentals

• Core Java Concepts: Variables, data types, operators, control structures, object-oriented programming (OOP) principles (classes, objects, inheritance, polymorphism, abstraction, encapsulation), exception handling, and multithreading.
• Data Structures and Algorithms: Understanding and implementing various data structures (arrays, lists, maps, sets, queues) and algorithms for efficient problem solving.
• Java APIs: Working with essential Java APIs like Java I/O, Collections Framework, and Java 8 features (lambda expressions, streams, functional interfaces, date and time API).
• Build Tools: Using Maven for managing project dependencies and builds. 

2. Database management and data persistence

• Database Concepts: Introduction to relational databases (RDBMS) like MySQL and NoSQL databases like MongoDB.
• SQL: Writing SQL queries for database interaction (DDL, DML, DQL), including joins, stored procedures, and transactions.
• JDBC (Java Database Connectivity): Connecting Java applications to databases, performing CRUD operations, and understanding JDBC drivers and architectures.
• ORM (Object-Relational Mapping): Using frameworks like Hibernate and JPA (Java Persistence API) to simplify database interactions, map Java objects to database tables, and reduce the need for explicit SQL queries.
• Spring Data JPA: Leveraging Spring Data JPA for easy repository creation and data access layer implementation. 

3. Web application development

• Servlets and JSP (JavaServer Pages): Understanding server-side programming with Servlets and creating dynamic web content with JSP, along with their lifecycles, communication, and session management.

Web Frameworks:

• Spring Framework: Core concepts like Dependency Injection (DI) and Inversion of Control (IoC), Aspect-Oriented Programming (AOP), Spring MVC for building web applications and RESTful services, Spring Security for authentication and authorization, and integration with databases and other modules.
• Spring Boot: Rapid application development with Spring Boot's auto-configuration and embedded servers, simplifying project setup and deployment.
• RESTful APIs: Designing, implementing, and consuming RESTful web services in Java, using Spring Boot or other frameworks.
• Microservices Architecture: Understanding the principles of microservices, building and deploying microservices with Spring Boot and Spring Cloud, inter-service communication, service discovery, API gateways, and fault tolerance. 

4. Security

• Security Principles: Understanding common security threats like SQL injection and cross-site scripting (XSS), implementing authentication and authorization mechanisms, and securely handling data, 
• Spring Security: Using Spring Security for robust authentication and authorization in Spring applications.
• Authentication and Authorization Protocols: Implementing and using protocols like OAuth 2.0, Open ID Connect, and JWT (JSON Web Tokens). 

5. Deployment and testing

• Testing Frameworks: Using JUnit for unit testing, and potentially other frameworks for integration and end-to-end testing.
• Continuous Integration/Continuous Deployment (CI/CD): Understanding the principles of CI/CD and potentially working with tools like Jenkins or GitLab CI/CD for automated builds and deployments.
• Deployment Strategies: Deploying Java backend applications to cloud platforms (like Google Cloud App Engine) or using containerization technologies (like Docker) and orchestration tools (like Kubernetes). 

6. Advanced topics (optional)

• Reactive Programming: Understanding and implementing reactive programming paradigms with Java and Spring.
• Caching: Implementing caching mechanisms to improve application performance.
• Message Brokers: Integrating message brokers like Apache Kafka for asynchronous communication between microservices.
• Cloud Integration: Integrating with various cloud services and understanding cloud-native development practices.