What is the difference between singleton and prototype bean scopes?
Table of Contents
Introduction
In Spring, bean scopes define the lifecycle and visibility of beans within the application context. The two most commonly used scopes are singleton and prototype. Understanding the differences between these scopes is crucial for managing resources and designing efficient applications.
Singleton Bean Scope
Definition
- Singleton Scope: A singleton bean is created once per Spring IoC container. All requests for the bean return the same instance.
Characteristics
- Single Instance: Only one instance of the bean is created and shared throughout the application.
- Default Scope: This is the default scope in Spring, meaning if no scope is specified, Spring will treat the bean as a singleton.
- Resource Management: Since a single instance is reused, it can be more efficient in terms of memory usage.
Usage
- Shared Components: Ideal for services or components that maintain shared state or configuration.
- Thread Safety: Singleton beans can lead to thread-safety issues if not designed carefully, especially if mutable state is involved.
Example
Prototype Bean Scope
Definition
- Prototype Scope: A prototype bean creates a new instance every time it is requested from the Spring container.
Characteristics
- Multiple Instances: Each request for the bean results in a new instance, providing unique state for each usage.
- Lifecycle Management: Spring does not manage the complete lifecycle of prototype beans. While Spring creates the bean, it does not handle its destruction.
- Memory Overhead: Can lead to higher memory usage since a new instance is created for each request.
Usage
- Stateful Objects: Suitable for beans that need to maintain unique state or data across multiple invocations.
- Request-Specific Data: Often used for user-specific services in web applications.
Example
Key Differences
| Feature | Singleton Scope | Prototype Scope |
|---|---|---|
| Instance Count | One instance per Spring container | New instance for each request |
| Lifecycle Management | Managed completely by Spring | Spring manages creation, not destruction |
| Default Behavior | Default scope in Spring | Must be explicitly defined using @Scope |
| Memory Usage | More efficient due to shared instances | Can be memory-intensive due to multiple instances |
| Thread Safety | May require synchronization for shared state | Each instance is unique, reducing threading issues |
| Use Case | Shared services or stateless components | Stateful components or user-specific data |
Conclusion
Understanding the differences between singleton and prototype bean scopes in Spring is essential for effective application design. Singleton beans are suitable for shared resources and stateless components, while prototype beans are ideal for stateful objects that require unique instances. Properly managing these scopes allows developers to optimize resource usage and application performance.