Java EE 6 overview

Java EE 6 overview

Starting from this lesson you’ll be learning about Java Enterprise Edition (Java EE or formerly J2EE), which is a powerful, mature, and widely used platform for development of distributed applications. The word enterprise here doesn’t imply that it is only for large-scale applications.

Java EE components are used for the development of everything from an application for a local pizza parlor’s website running on a five-hundred-dollar computer to a super-powerful Wall Street trading application that runs on a cluster of hundreds of interconnected servers.

Java EE 6 is the most current platform and the easiest to use. It was released in December 2009.

Java EE tiers are implemented in containers. It’s easy to guess that containers were created to contain something. In the Java EE world containers not only contain, but also control the birth, life, and death of Java components. For example, you don’t need to write the new statement to create a new instance of an EJB; the container will create a pool of them based on configuration parameters. Even on the client side, while reading about applets you might have noticed that applets’ life cycles are controlled by the JRE, which can be called an applet container. Basically, a container is an area inside JVM that can support a lifecycle of certain types of Java objects, such as applets, servlet, EJB, etc.

Containers can take care of various functions, and one of them is thread safety. It’s great that multiple clients can connect and make requests to the same server, but can you be sure that a thread initiated by Mary won’t interfere with John’s thread? An EJB container implements a single-threaded model ensuring that each client’s request operates in a dedicated thread. Containers may offer transactional support with Java Transaction API (JTA) and persist data for you with Java Persistence API (JPA).

The Java EE is a specification, and when a release is published, vendors who want to implement it in their software products create application servers that support this specification. Multiple vendors offer their versions of a Java EE application server. The question is what version of the Java EE specification they support. Currently the application servers GlassFish (Oracle) and JBoss (Red Hat) support Java EE 6. At the time of this writing WebLogic (Oracle) and WebSphere(IBM) are still on Java EE 5, but should offer support of the latest specification soon.

Java EE application servers have to support multiple containers, for example a Servlet container and an EJB container. Some vendors prefer to create products supporting only certain technologies defined in the Java EE specification. For example, Tomcat (Apache), Jetty (Eclipse Foundation), and Resin (Caucho) offer support for selected technologies (such as Servlets and JSP), which makes them suitable for implementing web applications, but if you are planning to create web applications based on one of these products, you’ll need to figure out what other tools or frameworks will be needed to support transactions, the business tier, data persistence, and more.

Servlet and EJB containers are scalable and they take care of all multi-threading issues, enabling you to write application code as if the application were the only user.Java EE is a very robust, reliable, and scalable platform and you will appreciate what its container will do for your code.

Java EE implements dependency injection. An object doesn’t have to reach out to get the resources

it needs, because the container injects the resources into the object using annotations.

Interceptors offer a mechanism by which containers can intercept method invoked on your session beans. When the call is intercepted you can specify additional code to be called before or after the method is executed. For example, imagine that you need to add logging before certain methods are called. Adding interceptors is an easy way to do this.

Integration of Java EE 6 with third-party web frameworks like Spring and Hibernate is made easy by web fragments.