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New Features in Java EE 6 : Page 2

Get a sneak preview of the new modularity and lightweight features in Java EE 6.


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Enterprise JavaBeans 3.1

One of the main goals of the EJB 3.1 specification is to make EJB as simple as possible. The idea is to provide more emphasis on simplifying EJB architecture while introducing new functionalities. Some of the important changes in EJB 3.1 are:

  • Removal of local business interface: EJB 3.0 removed the complex home and remote interfaces and made way for the plain old Java interface (POJI). EJB 3.1 goes one step further by dictating that business interfaces also are not mandatory. Similar to POJOs such as entities in JPA and message-driven beans, developers can write session beans without business interfaces in Java EE 6:

    @Stateless public class StockQuoteBean { public double getStockPrice(String symbol) { ... } }

  • Introduction of Singleton beans: The concept of Singleton beans was introduced primarily to share application-wide data and support concurrent access. When a bean is marked as a Singleton, the container guarantees a single instance per JVM that is shared across the application tier. This provision works well for caching. Singleton beans are like any other EJBs; they are POJOs that developers can mark as Singleton beans through annotations.
    All Singleton beans are transactional and thread safe by default, making way for flexible concurrency options. Java EE 6 also introduces concurrency annotations to perform locked read/write operations on getter and setter methods.


    @Singleton @Startup public class CounterBean { private int count; @PostConstruct public void initialize() { count=5; } }

  • Packaging EJB components directly in a WAR file: One of the major advancements in EJB 3.1 is the option for including EJB in a WAR file directly instead of creating a separate JAR file. EJB 3.1 provides a simplified packaging mechanism for web applications, including EJBs. Figure 2 shows how packaging was done prior to EJB 3.1.
    With EJB 3.1, developers can place the EJBs directly under the classes directory in the WAR file, along with the servlets. Figure 3 shows packaging in EJB 3.1.

    Figure 2. Post List Page with Tags: This is how packaging was done prior to EJB 3.1.
     
    Figure 3. EJB 3.1 Packaging Structure: Here is packaging in EJB 3.1.
  • Embeddable API for executing EJB in Java SE environment: The idea behind this feature is to allow EJBs to run in Java SE environments; that is, the client and the EJB run in the same JVM. To run EJBs, Java EE 6 provides an embedded EJB container and uses JNDI for lookup. This is to facilitate better support for testing, batch processing, and using EJB from the desktop applications. The embeddable EJB container provides an environment to manage EJB. The environment supports a limited set of services. The javax.ejb.EJBContainer class represents an embeddable container.
  • Asynchronous Session Bean: A session bean can support asynchronous method invocations. Bean methods annotated with @Asynchronous are invoked asynchronously. Prior to EJB 3.1, any method invocation on a session bean was always synchronous.
    Asynchronous methods can return a Future<V> object of the java.util.concurrent API. This will be useful for the client to get the status of the invocation, retrieve the return value of a method, check for an exception, or even cancel the invocation.
    Figure 4. EJB 3.1 Lite vs. EJB 3.1 Full: Here is a list of features supported in the full EJB API versus those supported in EJB Lite.
  • EJB Lite: The concept of profiles is applied to the EJB specification as well. Many enterprise applications do not require the complete set of features in EJB, so EJB Lite, a minimal subset of the EJB API, is introduced in EJB 3.1. EJB Lite includes all the features required for creating an enterprise application, but it excludes specialized APIs.
    EJB Lite provides vendors the option to implement a subset of the EJB APIs within their products. Applications created with EJB Lite can be deployed on any server that supports EJB technology, irrespective of whether it is full EJB or EJB Lite. Embeddable containers support EJB Lite.
    EJB Lite has the following subset of the EJB API:
    • Session bean components (Stateless, stateful, singleton session beans)
    • Supports only synchronous invocation
    • Container-managed and bean-managed transactions
    • Declarative and programmatic security
    • Interceptors
    • Support for deployment descriptor (ejb-jar.xml)
    The list of features supported in the full EJB API versus those supported in EJB Lite is shown in Figure 4.



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