"This article proposes a simple alternative: clustering POJOs at the JVM level. It discusses what JVM-level clustering is, how it works, and how it performs. It also explores how developers can leverage POJO clustering in order to solve real day-to-day problems with existing frameworks, as well as how POJO clustering might form the core of a POJO container?a new application container to provide enterprise-class operations based on simple user library and JDK library objects."
"Long before the EJB 3 specification was written, some developers disillusioned with EJB started to look for alternative frameworks. POJOs are an especially compelling alternative to EJBs. A POJO is simply a Java object that does not implement any special interfaces such as those defined by the EJB framework. The name was coined by Fowler, Rebbecca Parsons, and Josh MacKenzie [Fowler POJO] to give regular Java objects an exciting-sounding name. Later in this section you will see how this simple idea has some surprisingly important benefits."
"Most applications consist of multiple components that need to access one another. A traditional J2EE application uses JNDI as the mechanism that one component uses to access another. For example, the presentation tier uses a JNDI lookup to obtain a reference to a session bean home interface. Similarly, an EJB uses JNDI to access the resources that it needs, such as a JDBC DataSource. The trouble with JNDI is that it couples application code to the application server, which makes development and testing more difficult. The Spring framework provides POJOs with a much easier-to-use mechanism called dependency injection, which decouples application components from one another and from the application server."
"There are several lightweight mechanisms for making POJOs transactional. One very popular framework that provides this capability is Spring. Spring is a powerful J2EE application framework that makes it significantly easier to develop enterprise Java applications. It provides a large number of features, and I'm only going to provide a brief overview of a few of them in this article. For more information see Spring in Action [Walls 2005]."
