Autowired In Spring:

What is Autowiring in Spring?

When can use @Autowired Annotation?

Where can we use @Autowired Annotation?

In the Spring Framework, autowiring is a feature that allows automatic dependency injection.

 It is a way of wiring beans (components) together by letting Spring automatically resolve and inject the dependencies between them, without explicitly configuring each dependency.


Autowiring simplifies the configuration process by reducing the amount of XML or Java-based configuration code needed to wire beans together. 

It promotes loose coupling and makes the code more maintainable and flexible.


There are different modes of autowiring in Spring:


ByType Autowiring:

In this mode, Spring looks for a bean of the same data type (or its subtype) as the dependency and automatically injects it.

If there are multiple beans of the same type, an exception is thrown, unless the dependency is marked as optional.

ByName Autowiring:

In this mode, Spring looks for a bean with the same name as the dependency and injects it.

The name of the dependency is matched with the name of the corresponding bean in the Spring container.

Constructor Autowiring:

With constructor autowiring, Spring analyzes the constructor arguments and matches them with beans available in the container based on their data types.

The constructor with the best matching arguments is selected for dependency injection.

No Autowiring:

In this mode, autowiring is disabled, and dependencies must be explicitly wired using configuration annotations or XML.

To enable autowiring in Spring, you typically annotate the dependent bean or use XML configuration.

 The most common annotations for autowiring in Spring are @Autowired, @Qualifier, and @Resource.

 These annotations are used to mark the dependencies and specify the autowiring mode or to provide additional information for resolving dependencies.


Here's an example that demonstrates autowiring using the @Autowired annotation:


@Component 
public class MyClass { 
private MyDependency dependency;
@Autowired 
public MyClass(MyDependency dependency) {
this.dependency = dependency;
 } 
// ...
}

In the above example, the MyClass component has a dependency on MyDependency.

 The @Autowired annotation on the constructor indicates that the dependency should be automatically injected by Spring.


When Spring creates an instance of MyClass, it automatically looks for a bean of type MyDependency and injects it into the constructor.


Autowiring simplifies the configuration and reduces the need for manual wiring, making the code more concise and maintainable. 

It allows for loose coupling and facilitates the development of modular and flexible Spring applications.