Stateless Stateful

What is State?

State is information an application remembers, such as the selected patient or logged-in user.

What is Stateless?

A stateless component processes each request without relying on client information remembered from previous requests. Each request supplies the necessary inputs.

Example: You send the patient ID every time you request that patient's details.

What is Stateful?

A stateful component remembers information between requests and uses it in later interactions.

Example: You select a patient once. The application remembers the selection and uses it when you request the selected patient's details.

Stateless versus Stateful

Feature	Stateless	Stateful
Previous client information	Does not rely on remembered information	Remembers information between requests
Request inputs	Supplies the required context each time	Can reuse saved context
Example	Send patient ID with every lookup	Remember the selected patient
Multiple servers	Easier to distribute requests	Saved state must be available to the next server
Database access	Can read and write data	Can read and write data

Note: Stateless does not mean “no database.” Database records and temporary session information are different.

Diagram

This diagram compares two possible designs for viewing patient details.

sequenceDiagram
    participant B as Browser
    participant S as Stateless service
    participant F as Stateful service

    B->>S: Get details using patient ID
    S-->>B: Patient details
    Note over S: No saved patient selection required
    B->>S: Send patient ID again
    S-->>B: Patient details

    B->>F: Select a patient
    Note over F: Remember selection in session
    F-->>B: Selection saved
    B->>F: Show selected patient's details
    F-->>B: Use remembered selection

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Examples in HMIS

• Stateful behavior: SessionController uses @SessionScoped to remember information such as the logged-in user and selected department.
• Stateless EJB: PatientFacade uses @Stateless for database operations without retaining a client conversation.

@SessionScoped and @Stateful are different Java annotations. A controller can have stateful behavior without being an @Stateful EJB.