How Dependency Injection Works in Spring?
- Components: In a Spring application, you typically define various components, such as classes or beans, that represent different parts of your application’s functionality.
- Dependencies: These components often have dependencies on other components or services to perform their tasks effectively.
- Configuration: You configure your Spring application using XML-based configuration files, Java annotations, or Java-based configuration classes (using @Configuration and @Bean annotations).
- Injection: Spring’s IoC container manages the creation of objects and their dependencies. When a component needs a dependency, the container injects it at runtime, ensuring that the required objects are available and correctly initialized.
There are two primary ways to perform Dependency Injection in Spring:
- Constructor Injection: Dependencies are injected through the constructor of the dependent class. This is the most common and recommended approach because it ensures that the dependent object is fully initialized when it’s created.
- Setter Injection: Dependencies are injected through setter methods in the dependent class. While less common than constructor injection, setter injection can be useful in scenarios where you have optional dependencies or need to change dependencies at runtime.
The below example illustrates Java Spring’s Dependency Injection:
Java
public class CricbuzzApp { private CricbuzzService cricbuzzService; // Constructor Injection public CricbuzzApp(CricbuzzService cricbuzzService) { this.cricbuzzService = cricbuzzService; } public void run() { myService.doSomething(); } } public interface CricbuzzService { void doSomething(); } public class CricbuzzServiceImpl implements CricbuzzService { @Override public void doSomething() { System.out.println("Doing something in CricbuzzServiceImpl."); } } |
Spring – When to Use @Qualifier and @Autowired For Dependency Injection
In the world of Spring Framework, managing dependencies is a fundamental aspect of building robust and maintainable applications. Spring offers two primary annotations to facilitate dependency injection: @Autowired and @Qualifier. Understanding when and how to use these annotations is crucial for effective bean wiring .@Autowired and @Qualifier are both annotations used in Spring Framework to work with dependency injection, but they serve different purposes.
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