Guidelines, Patterns, and code for end-to-end Java applications.
Questions and Answers - Session state in the EJB tier
- How can state be maintained in the EJB tier, and what are the
tradeoffs involved?
1. How can state be maintained in the EJB tier, and what are the
tradeoffs involved?
A session is a sequence of service requests by a single user
using a single client to access a server. The information maintained
in the session across requests is called session state.
Session state may include both information visible to the user
(shopping cart contents, for example) and invisible application
control information (such as user preferences).
We recommend that:
A stateful session bean is a session bean that maintains
session state. Stateful session beans have a one-to-one correspondence
with user sessions. Each user session that uses a stateful session
bean will have a corresponding instance of that bean on the EJB
server. (This is contrasted with stateless session beans, which may be
shared between users.)
The Java Pet Store sample application version 1.1.1 uses stateful session
beans to maintain session state in the EJB tier
(in classes ShoppingClientControllerEJB,
CustomerEJB, and
AdminClientControllerEJB).
These stateful session beans act as facades, managing access
to finer-grained enterprise beans and handling the details of accessing
these beans based on user identity (enterprise beans
CustomerEJB,
ProfileMgrEJB,
ShoppingCartEJB,
AccountEJB,
OrderEJB). The
Session Entity Facade design pattern explains this design in more detail.
Some applications do not need the power or overhead of enterprise beans. In
these situations, we recommend
storing client session state in the
web tier, using the
HttpSession interface implemented for your server.
|
|
Print-friendly Version
