Introduction to Jakarta EE
Jakarta EE, formerly known as Java EE, is the gold standard for building scalable, multi-tier enterprise applications in Java. It provides a rich set of specifications covering everything from web-tier components like Servlets and JSP to advanced enterprise services such as CDI and EJB. Additionally, Jakarta EE offers robust support for both RESTful and SOAP web services, making it a complete platform for modern server-side development.
Core Platform and Concepts
Before diving into specific APIs, it's essential to understand the foundational elements of Jakarta EE. This includes deploying applications, understanding naming and directory services, and choosing the right server. Key topics include:
- Deployment: How to deploy a WAR file to popular servers like Tomcat.
- Migration: Moving from the older Java EE to the newer Jakarta EE namespace.
- Naming and Directory: An overview of JNDI (Java Naming and Directory Interface).
- Historical Context: The evolution from J2EE to Java EE to Jakarta EE.
- Server Options: Web and application servers that support Jakarta EE, including the latest Jakarta EE 10 release.
Web Tier: Servlets, JSP, and JSF
Servlets
Servlets are the backbone of Jakarta EE web applications, handling HTTP requests and responses. This section covers:
- Introduction to Java Servlets and servlet containers.
- Managing user state with cookies and sessions.
- Registering servlets programmatically or via annotations.
- Understanding redirect vs. forward techniques.
- Returning JSON responses from servlets.
- Exception handling in a servlet environment.
JSP and JSF
JavaServer Pages (JSP) and JavaServer Faces (JSF) are powerful view technologies. Key guides include:
- Guide to JavaServer Pages (JSP) – creating dynamic web pages.
- Introduction to PrimeFaces, a popular JSF component library.
- JSTL Library – using standard tag libraries for common tasks.
- MVC Example – combining servlets and JSP in a model-view-controller pattern.
- JSF EL 2 – understanding Expression Language in JSF.
Web Services: JAX-RS and JAX-WS
Jakarta EE fully supports both RESTful and SOAP web services. This section covers:
JAX-RS (REST)
- Understanding that JAX-RS is just an API – implementations like Jersey provide the runtime.
- Using the JAX-RS Client with Jersey for consuming REST APIs.
- Filters and Interceptors in Jersey for cross-cutting concerns.
- Server-Sent Events (SSE) for real-time communication.
- Setting a custom response body in JAX-RS.
JAX-WS (SOAP)
- Introduction to JAX-WS for building SOAP-based web services.
- Consuming a SOAP web service from a Java client.
- Using Apache CXF as a framework for both JAX-WS and JAX-RS.
Bean Validation
Jakarta Bean Validation provides a standard way to enforce data integrity. This section dives into the core concepts:
- Bean Validation basics – applying constraints on fields and properties.
- Differences between @NotNull, @NotEmpty, and @NotBlank constraints.
- Validating enum types effectively.
- Grouping constraints for partial validation scenarios.
- Method constraints with Bean Validation 3.0 – validating method parameters and return values.
- Using the @Valid annotation for cascading validation on child objects.
- List annotations for validating collections.
- Container element validation – a new feature in Jakarta Bean Validation 3.0.
CDI and EJB
Contexts and Dependency Injection (CDI)
CDI is the core dependency injection framework in Jakarta EE. Topics include:
- Introduction to CDI – managing beans and their lifecycle.
- Event Notification Model in CDI 2.0 for loosely coupled communication.
Enterprise JavaBeans (EJB)
EJB provides business logic components with built-in services like transactions and messaging. This section covers:
- Setting up EJB in a Jakarta EE environment.
- Session Beans – stateless, stateful, and singleton patterns.
- Message-Driven Beans (MDB) for asynchronous processing using JMS.
- Jakarta EE JTA – managing distributed transactions.
- Singleton Session Beans – ensuring a single instance per application.
Conclusion
Jakarta EE remains a robust and evolving platform for enterprise Java development. From the web tier with Servlets and JSF to services via JAX-RS and JAX-WS, and from data validation with Bean Validation to business logic management with CDI and EJB, the platform offers a comprehensive toolkit. By mastering these core APIs, developers can build scalable, maintainable server-side applications that meet modern enterprise demands.