Dependency Injection (DI) is a core concept in the Spring Framework, designed to make your code more modular, testable, and maintainable. It works by transferring the responsibility of managing dependencies (objects a class relies on) to the Spring container. This allows you to focus on building features without worrying about creating and managing object instances manually.
How Dependency Injection Works
In Spring, DI enables you to inject objects into other objects, typically using configurations like XML, Java annotations, or Java-based configurations. For instance, instead of writing code to create dependencies using the new keyword, you declare them, and Spring wires everything for you automatically.
Benefits of Dependency Injection
- Loose Coupling: Classes depend on abstractions, not concrete implementations, making it easy to swap dependencies.
- Simplified Testing: You can easily mock or replace dependencies in unit tests without modifying the original code.
- Centralized Configuration: All dependency configurations are managed in a single place, improving clarity and reducing errors.
Example
Here's an example of constructor-based DI using annotations:
@Componentpublic class Car {
private Engine engine;
@Autowired
public Car(Engine engine) {
this.engine = engine;
}
public void drive() {
engine.start();
System.out.println("Car is driving...");
}
}
In this example, Spring automatically injects an instance of Engine into the Car class when needed.
Conclusion
Dependency Injection in Spring simplifies object management by delegating it to the framework. This leads to cleaner code, better flexibility, and easier maintenance.
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