A java bean is a simple data structure which is responsible for carring data and not complex logic.
You should determine the rules for getting and setting attibutes but nothing beyond this. Coding this way, the final result will show lots of classes with the responsibility well distributed. Each class has its own role in the system and data structure is the java bean responsibility. It's like a style of coding.
There are some advantages using these beans, like the built-in facilities in the
servlet engine.
Think of the use of the tag
jsp:useBean, for instance. It is really useful.