🌱 Spring Bean Scopes

Spring beans don’t all live the same life. Some are long-term residents, others are quick visitors who grab a coffee and vanish ☕🚪

Bean scope decides how long a bean lives and how many instances exist.

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🔹 1. Singleton (Default)

👉 One bean per Spring container

@Component
@Scope("singleton") // optional (default)
class MyService {}

🧠 Behavior

• Same instance reused everywhere
• Created once at startup

✅ Use When

• Stateless services
• Shared resources

⚠️ Caution

• Not thread-safe by default

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🔹 2. Prototype

👉 New bean every time it is requested

@Component
@Scope("prototype")
class MyService {}

🧠 Behavior

• Every getBean() → new object
• Spring does NOT manage full lifecycle (no destroy)

✅ Use When

• Stateful objects
• Temporary processing

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🔹 3. Request Scope (Web)

👉 One bean per HTTP request

@Component
@Scope("request")
class RequestBean {}

🧠 Behavior

• New instance for each request
• Destroyed after request ends

✅ Use When

• Request-specific data
• User input handling

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🔹 4. Session Scope (Web)

👉 One bean per HTTP session

@Component
@Scope("session")
class SessionBean {}

🧠 Behavior

• Shared across requests in same session

✅ Use When

• User session data
• Shopping cart

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🔹 5. Application Scope (Web)

👉 One bean per ServletContext

@Component
@Scope("application")
class AppBean {}

🧠 Behavior

• Shared across entire web app

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🔹 6. WebSocket Scope

👉 One bean per WebSocket session

@Scope("websocket")

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🔄 Summary Table

Scope	Instances	Lifecycle	Use Case
Singleton	1	App-wide	Services
Prototype	Many	Partial	Stateful objects
Request	Per request	Request	API data
Session	Per session	Session	User data
Application	1 per app	App	Global config

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⚠️ Important Interview Trap

❗ Singleton + Prototype together

@Autowired
private PrototypeBean prototypeBean;

👉 Problem:

• Prototype injected only once into singleton 😬

✅ Solution:

Use:

• ObjectProvider
• ApplicationContext.getBean()

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🎯 Interview Answer

“Spring supports multiple bean scopes like singleton, prototype, request, session, and application. Singleton is the default and creates a single shared instance, while prototype creates a new instance on each request. Web scopes like request and session are used in web applications for managing request-specific and user-specific data.”

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🧠 Mental Model

Think of scopes like hotel rooms 🏨:

• Singleton → one VIP suite (shared)
• Prototype → new room every booking
• Request → room for one visit
• Session → room for entire stay