POJO vs EJB vs EJB 3
Does anyone have any example of what a Java Class might look like as a POJO, EJB, and EJB 3? I'm trying to understand these java technologies but am having trouble. I was hoping it would help if I could see what an implementation of all three would look like.
Answer
POJO stands for Plain-Old-Java-Object - just a normal Java class as opposed to older technologies that required changing the class in specific ways to make it work with their framework.
class MyService {
public String sayHello() { return "hello world"; }
}
As such POJOs can be used anywhere a normal class can be used. However if you want to build an enterprise application out of them you still need some framework - Spring is a good example of a framework that can work directly with POJOs.
EJB2 is no longer relevant so you can ignore it - unless you need to maintain some legacy code. To satisfy your curiosity the same example as above would require several classes and xml descriptors to make it run - it's easy to see why it became obsolete.
EJB3 is the latest standard for developing enterprise applications which replaces EJB2 and is based on concept of taking POJOs and annotating them so that they can be used in enterprise app.
@Stateless
class MyService {
public String sayHello() { return "hello world"; }
}
As you can see it's very similar to POJOs. In fact most application written for EJB3 can easily be converted to work with Spring, and usually the other way works too.