Introduction to Enterprise JavaBeans
In the last module, we explored the world of distributed objects and looked at how components can be managed and combined to create flexible applications.
Enterprise JavaBeans are distributed objects .
In this module, we look at Enterprise JavaBeans and how the EJB architecture relates to that of distributed objects in general.
Enterprise JavaBeans are also known as EJBs and, for simplicity, I will refer to them as a bean or beans.
A "bean instance" or "bean object" indicates an actual instance of a bean.
Exploring EJB architecture
The first lesson will remove any myths or confusion regarding Java's notion of JavaBeans versus Enterprise JavaBeans.
I will then explain how the EJB architecture fits the Object Monitor (OM) model and describe in detail the contract that the bean has, and the one that the client has, with the container.
We will explore the plumbing (system services) that the EJB server container combination provides to, and on behalf, of the bean.
Types of beans
In the next few lessons, we will look at the three types of EJBs:
stateful session beans, stateless session beans, and entity beans.
We will look at how you can declaratively specify the deployment parameters for a bean in a deployment descriptor
and package the beans in jar files
for ease of handling.
- Deployment descriptor: Information that describes both the structure of an Enterprise Java Bean, and the information required by it at runtime.
- Jar file: A file created with the Java jar program which is similar to tar on the Unix platform.
In the next lesson, the difference between Enterprise JavaBeans and JavaBeans will be discussed.