Passing objects by value is tricky with Enterprise JavaBeans. Two simple rules will keep you out of most problem areas: objects that are passed by value should be fine-grained dependent objects or wrappers used in bulk accessors, and dependent objects should be immutable.
The concept of dependent objects was addressed in Chapter 6, which describes the use of dependent objects in EJB 2.0. But for EJB 1.1, dependent objects are a new concept. EJB 2.0 and EJB 1.1 use dependent objects differently, because EJB 2.0 can accommodate much more fine-grained entity beans than EJB 1.1.
Dependent objects are objects that have meaning only within the
context of another business object. They typically represent fairly
fine-grained business concepts, such as an address, phone number, or
order item. For example, an address has little meaning when it is not
associated with a business object such as
Organization. It depends on the context of the
business object to give it meaning. Such an object can be thought of
as a wrapper for related data. The fields that make up an address
zip) should be
packaged together in a single object called
AddressDO. In turn, the
AddressDO object is usually an attribute or
property of another business object; in EJB, we would typically see a
dependent object such as
AddressDO as a property
of an entity bean.
Here’s a typical implementation of an
public class AddressDO ...