EJB2 vs. EJB3

Attribute	EJB2	EJB3
Version	EJB2	EJB3
Component Model	Container-Managed	POJO-Based
Annotations	Not Supported	Supported
Dependency Injection	Not Supported	Supported
Local Interfaces	Required	Optional
Remote Interfaces	Required	Optional
Transaction Management	Container-Managed	Container-Managed or Bean-Managed
Persistence	Entity Beans	JPA (Java Persistence API)
Callback Methods	ejbCreate(), ejbRemove(), etc.	@PostConstruct, @PreDestroy, etc.
Exception Handling	Checked Exceptions	Unchecked Exceptions

Introduction

Enterprise JavaBeans (EJB) is a server-side component architecture that enables developers to build scalable, distributed, and transactional applications. EJB2 and EJB3 are two major versions of the EJB specification, each with its own set of features and improvements. In this article, we will compare the attributes of EJB2 and EJB3, highlighting the advancements and benefits introduced in the latter version.

Component Model

EJB2 introduced the concept of session beans, entity beans, and message-driven beans as the primary components. Session beans represent business logic and are stateful or stateless. Entity beans represent persistent data and are typically mapped to database tables. Message-driven beans handle asynchronous messaging. However, EJB2 had a complex programming model with heavyweight components, requiring extensive configuration and deployment descriptors.

EJB3 simplified the component model by introducing annotations, reducing the need for deployment descriptors. It introduced the concept of plain old Java objects (POJOs) as session beans, eliminating the need for complex interfaces and extending specific EJB classes. This made the development process more intuitive and less cumbersome.

EJB3 also introduced the Java Persistence API (JPA), which provided a standardized approach for object-relational mapping (ORM). JPA made it easier to work with entity beans by simplifying the mapping between Java objects and database tables, reducing the amount of boilerplate code required.

Dependency Injection

EJB2 relied on the Java Naming and Directory Interface (JNDI) for dependency lookup and injection. Developers had to manually perform JNDI lookups to obtain references to other EJB components or resources. This approach was error-prone and increased the complexity of the code.

EJB3 introduced a built-in dependency injection (DI) mechanism, eliminating the need for manual JNDI lookups. With DI, developers can simply annotate the dependencies in their EJB classes, and the container takes care of injecting the required resources at runtime. This greatly simplifies the development process and improves code readability and maintainability.

Furthermore, EJB3 introduced the concept of container-managed transactions (CMT), where transaction management is handled by the EJB container. This relieved developers from managing transaction boundaries explicitly, reducing the chances of errors and improving the overall robustness of the application.

Lightweight Containers

EJB2 required a heavyweight container, which added significant overhead and complexity to the deployment and execution of EJB applications. The container was responsible for managing the lifecycle, concurrency, and resource pooling of EJB components.

EJB3 introduced lightweight containers, which were designed to be more modular and flexible. The container was decoupled from the EJB specification, allowing developers to choose from various lightweight containers, such as Spring or Java EE application servers. This gave developers more freedom and flexibility in deploying and running their EJB applications.

The lightweight containers in EJB3 also improved the startup time and memory footprint of EJB applications, making them more efficient and scalable. This was a significant improvement over EJB2, where the heavyweight container often resulted in slower application startup and higher resource consumption.

Asynchronous Processing

EJB2 provided support for asynchronous processing through message-driven beans. However, the programming model for asynchronous processing was complex and required developers to implement specific interfaces and methods.

EJB3 introduced a simplified and more intuitive programming model for asynchronous processing. It introduced the @Asynchronous annotation, which could be applied to methods in session beans to indicate that they should be executed asynchronously. This made it easier to write code that could handle long-running or non-blocking operations without blocking the main thread.

The improved support for asynchronous processing in EJB3 made it easier to build responsive and scalable applications that could handle concurrent requests and perform background tasks efficiently.

Conclusion

EJB3 brought significant improvements and advancements over EJB2, making it a more developer-friendly and efficient technology for building enterprise applications. The introduction of annotations, dependency injection, lightweight containers, and simplified asynchronous processing greatly simplified the development process and improved the overall performance and scalability of EJB applications.

While EJB2 served as a foundation for enterprise application development, EJB3 revolutionized the way developers approached building distributed and transactional applications. Its simplified programming model and improved features made it easier to develop, test, and maintain EJB applications, ultimately leading to increased productivity and better application performance.