Constructor Injection vs Setter Injection in Spring
Constructor Injection vs Setter Injection
| Feature | Constructor Injection | Setter Injection |
|---|---|---|
| Definition | In Constructor Injection, dependencies are provided through the class constructor. | In Setter Injection, dependencies are injected through public setter methods after the object is created. |
| When to Use | Best for mandatory dependencies, as these dependencies are required at the time of object creation. | Ideal for optional dependencies or cases where dependencies might need to be changed after the object has been created. |
| Object Creation | Dependencies are provided at the time of object creation, making them mandatory. | Dependencies can be set or modified after the object is created. |
| Immutability | Promotes immutability as dependencies are usually final after construction. | Allows mutable dependencies, as setters can be called to change dependencies later. |
| Readability and Clarity | Makes dependencies explicit and ensures they are provided when constructing the object. | Less explicit, as dependencies may or may not be provided after object creation. |
| Dependency Injection (DI) Framework Support | Supported by DI frameworks, often easier to implement for required dependencies. | Supported by DI frameworks, but may require additional configuration for optional dependencies. |
| Circular Dependency Handling | Can create issues with circular dependencies, as all dependencies must be resolved at creation. | Handles circular dependencies more gracefully, as dependencies can be set post-creation. |
| Testability | Good for testing as all dependencies are injected upfront, making it easy to provide mock dependencies. | Also testable, though less ideal for mandatory dependencies as it allows for later modifications. |
Use Case
- Constructor Injection is generally better for required dependencies, as it ensures that objects are created with all necessary dependencies. This improves code reliability and makes it clear that the dependency is mandatory.
- Setter Injection is preferable for optional dependencies or cases where we want to change the dependency post-creation. It can handle circular dependencies more easily but might lead to mutable dependencies, which can be a drawback for some use cases.
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