Working with Session Beans

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Working with Session Beans

• B.Ramamurthy

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Introduction

• We will session beans from two points of view
• the session bean developer who implements a
  session bean
• the client application programmer who uses the
  session bean

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When to use session beans

• Session beans is used to implement a stateful
  communication between a client and a server.
• A session object lasts for the duration of the
  clients session.
• The duration of a session is the time between the
  creation of the session bean and its removal.
• During this time, session bean stores the state
  information (conversational state) for the client.

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When to use .. (contd)

• Stateful session beans are suitable for the
  following situations
• To implement session logic of Web applications.
  One or more session beans can be used to
  implement the business process that drives the
  conversation with the user.
• Example Process that inputs billing and shipping
  information
• To implement session logic of traditional non-Web
  based applications. Ex Teller of a bank
  interacts with an application to enter multiple
  checks.

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Session Bean in Web Application
Business Logic
Form generation
Form Display
Web client
JSP, Servlets
Html over http
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Stateful vs Stateless Session Bean

• Session bean can stateful or stateless
• An instance of stateful session bean is
  associated with one client.
• One to one correspondence between session objects
  and instances of session bean class.
• Stateful session bean implements a
  conversational business process.
• state provides a convenient way of retaining
  client-specific state on the server.

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Stateless Session Bean

• Does not retain any client specific data.
• Container has pool of instances of stateless
  session beans and client requests are delegated
  to any available beans.
• Reused by different clients.
• Typically implements a procedural service on top
  of a database or legacy application.
• Ex PayRoll that simple gets db information to
  the user whose identity is given.

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Conversational State

• A stateful session bean keeps the server-side
  state on behalf of a single client.
• This may contain
• Data read from the database
• Information entered by the user.

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Example

• Application Benefits Enrollment
• Web application through which an employee manages
  his/her benefits selections.
• The application lets an employee enter, review,
  and change his/her selection of employer provided
  benefits.
• Three databases are involed payroll, employee
  and benefits

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User View

• User points to an URL.
• Application displays a sequence of HTML pages
  containing the various benefit choices available
  to the employee.
• After employee choice it display next screen.
• It also summarizes the selection.
• It also indicates the previous selection.
• After confirmation from the user the application
  updates information.
• There is a intial login page and final
  confirmation page besides the one shown on page
  62.

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Main Parts
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Benefits Enrollment Application
EJB Container1 Deploys PayrollEJB
Database Server Deploys PayrollDatabase
Benefits App Server
Web Container Deploys EnrollementWeb
Database Server Deploys EmployeeDatabase
EJB Container2 Deploys EnrollmentEJB
Enrollment App server
Database Server Deploys Benefits Database