Bean Scopes in Spring

A Bean Scope defines how many instances of a bean Spring creates and how long those instances live inside the Spring container.

Understanding bean scopes is important because:

• It affects memory usage
• It affects concurrency
• It affects lifecycle and garbage collection
• Wrong scope choice causes serious bugs

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What Is Bean Scope?

Bean scope answers two questions:

1. How many instances of a bean are created?
2. Who manages the bean lifecycle?

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Default Scope

Singleton is the default scope in Spring.

If you don’t specify a scope:

@Component
public class BranchService {
}

Spring creates ONE instance for the entire application.

Overview of Bean Scopes

Spring supports five main scopes:

Scope	Description
Singleton	One instance per container
Prototype	New instance per request
Request	One instance per HTTP request
Session	One instance per HTTP session
Application	One instance per ServletContext

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1️⃣ Singleton Scope (DEFAULT)

What It Means

• Only one instance per Spring container
• Shared across all requests and threads

@Service
@Scope("singleton")
public class BranchService {
}

Characteristics:

✔ Created at startup (eager by default)
✔ Destroyed on application shutdown
✔ Spring manages full lifecycle

Important Note (Concurrency)

Singleton beans:

• Are shared across threads
• Must be thread-safe
• Should NOT store request-specific state
• Stateless design is recommended.

Common Use Cases

• Services
• Repositories
• Controllers
• Utility beans

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2️⃣ Prototype Scope

What It Means

New instance every time the bean is requested

@Component
@Scope("prototype")
public class ReportGenerator {
}

Characteristics

✔ Created on demand
✔ Dependency injection happens
❌ Spring does NOT destroy it

Lifecycle Reminder (Important)

• Spring creates the bean
• Hands it to the caller
• Caller manages cleanup
• JVM GC handles memory

Common Use Cases

• Stateful objects
• Temporary objects
• Objects with short life

Caution ⚠️

Overusing prototype beans can cause:

• Memory leaks
• Object explosion

• Hard-to-debug issues

3️⃣ Request Scope (Web Only)

What It Means

• One instance per HTTP request

@Component
@Scope(value = WebApplicationContext.SCOPE_REQUEST)
public class RequestContext {
}

Characteristics

✔ Created at request start
✔ Destroyed after request completion
✔ Safe for request-specific data

Common Use Cases

• Request metadata
• Correlation IDs
• Request-scoped context objects

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4️⃣ Session Scope (Web Only)

What It Means

• One instance per HTTP session

@Component
@Scope(value = WebApplicationContext.SCOPE_SESSION)
public class UserSession {
}

Characteristics

✔ Shared across multiple requests
✔ Destroyed when session expires
❌ Can increase memory usage

Common Use Cases

• Logged-in user details
• Session preferences

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5️⃣ Application Scope (Web Only)

What It Means

• One instance per ServletContext
• Shared across the whole web application

@Component
@Scope(value = WebApplicationContext.SCOPE_APPLICATION)
public class AppConfigCache {
}

Characteristics

✔ Similar to singleton
✔ Servlet container–managed

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Singleton vs Prototype (VERY IMPORTANT)

Aspect	Singleton	Prototype
Instances	One	Many
Thread safety	Required	Not required
Lifecycle managed by Spring	Full	Partial
GC handled by	JVM	JVM
Typical usage	Services	Stateful objects

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Bean Scopes in Banking / Enterprise Systems

Common patterns:

• Singleton → Services, repositories
• Request → Request metadata, tracing
• Prototype → Rare, controlled usage
• Session → Minimal (stateless preferred)

Banking systems prefer stateless + singleton design.

Bean scope defines the lifecycle and visibility of a bean instance. Singleton is the default scope, prototype creates a new instance per request, and web scopes like request and session are used in web applications.