Friday, April 06, 2007

Dip Into Java EE 5

If you are considering moving to Java EE 5 soon and need to know what it's all about and how to get started on it, the following in a brief summary from a great book I've been reading (credits at end of post). Though examples are implemented on the JBoss AS, I did all of mine on Sun System Application Server 9.1 using the NetBeans 5.5 IDE and MySQL Community Server 5.x.

Java EE 5 provides a platform for developing and deploying multitiered, distributed applications that are designed to be maintainable, scalable, and portable. Just as an office building requires a lot of hidden infrastructure of plumbing, electricity, and telecommunications, large-scale applications require a great deal of support infrastructure. This infrastructure includes database access, transaction support, and security. Java EE provides that infrastructure and allows you to focus on your applications.

Building distributed applications (software with components that run as separate processes, or on separate computers) allows you to partition the software into layers of responsibility, or tiers. Distributed applications are commonly partitioned into three primary tiers: presentation, business rules, and data access. Partitioning applications into distinct tiers makes the software more maintainable and provides opportunities for scaling up applications as the demand on those applications increases. Java EE architecture is based on the idea of building applications around multiple tiers of responsibility. The application developer creates components, which are hosted by the Java EE containers.

Containers play a central theme in the Java EE architecture. Servlets are one type of Java EE web component. They are Java classes that are hosted within, and invoked by the Java EE server by requests made to, a web server. These Servlets respond to those requests by dynamically generating HTML, which is then returned to the requesting client.
JSPs are very similar in concept to Servlets, but differ in that the Java code is embedded within an HTML document. The Java EE server then compiles that HTML document into a Servlet, and that Servlet generates HTML in response to client requests.

JSF is a Java EE technology designed to create full and rich user interfaces. Standard user interface components are created on the server and connected to business logic components. Custom renderers take the components and create the actual user interface.

JDBC is a technology that enables an application to communicate with a data-storage system. Most often that is a relational database that stores data in tables that are linked through logical relations between tables. JDBC provides a common interface that allows you to communicate with the database through a standard interface without needing to learn the syntax of a particular database.

EJBs are the centerpiece of Java EE and are the component model for building the business rules logic in a Java EE application. EJBs can be designed to maintain state during a conversation with a client, or can be stateless. They can also be designed to be short-lived and ephemeral, or can be persisted for later recall. EJBs can also be designed to listen to message queues and respond to specific messages. Java EE is about a lot more than EJBs, although EJBs do play a
prominent role.

The Java EE platform provides a number of services beyond the component hosting of Servlets, JSPs, and EJBs. Fundamental services include support for XML, web services, transactions, and security. Extensive support for XML is a core component of Java EE. Support for both document-based and stream-based parsing of XML documents forms the foundation of XML support. Additional APIs provide XML registry service, remote procedure call invocation via XML, and XML-based messaging support.

Web services, which rely heavily on XML, provide support for describing, registering, finding, and invoking object services over the Web. Java EE provides support for publishing and accessing Java EE components as web services.
Transaction support is required in order to ensure data integrity for distributed database systems. This allows complex, multiple-step updates to databases to be treated as a single step with provisions to make the entire process committed upon success, or completely undone by rolling back on a failure. Java EE provides intrinsic support for distributed database transactions.
Java EE provides configurable security to ensure that sensitive systems are afforded appropriate protection. Security is provided in the form of authentication and authorization.

Additional notes:
• Containers provide an environment and infrastructure for executing Java EE components.
• Servlets and JSPs provide server-side processing and are used to create the presentation layer of a Java EE system.
• JSF provides user interface components that make it easy to create flexible user interfaces and connect user interface widgets to business objects.
• JDBC is an interface to database systems that allows developers to easily read and persist business data.
• EJBs represent business objects in a Java EE application. EJBs come in various categories, including stateful session beans, stateless session beans, entity beans, and messagedriven beans.
• Java EE systems can be used to develop service-oriented architectures or web services systems. A web service architecture is one that provides machine-to-machine services over a network using a well-defined protocol.
• Some of the essential architectural patterns used in Java EE applications include an application client with EJBs, a JSP client with EJBs, an applet client with JSPs and a database, and web services used for application integration.

[Beginning Java EE 5 - From Novice to Professional, pp. 26-28, Copyright © 2006 by Kevin Mukhar and Chris Zelenak, with James L. Weaver and Jim Crume]

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