How does @autowired annotation works for a private field?

Question

How does @Autowired annotation work for a private field without a getter and a setter? How can spring access a private field?

Answer 1

It works with reflection. Here you can find an example of how to set public fields. But setting private fields does not make much of a difference

The only difference with a private field is that you will need to set the setAccessible before you are able to read/write to the field. Further, this method can throw a SecurityException. Java Docs

Answer 2

@Component
public class A(){}

@Component
public class B(){
@Autowired
private A a;
}

Spring create beans mentioned as @Component. here bean A will be created first and since B is dependent on A, then injection of A to B is done. there's no need for any setters. just @Component is required. Spring uses CGLib for creation of beans using reflection.

Answer 3

Three types of dependency injection

There are at least three ways an object can receive a reference to an external module:

constructor injection: the dependencies are provided through a class constructor.

setter injection: the client exposes a setter method that the injector uses to inject the dependency.

interface injection: the dependency provides an injector method that will inject the dependency into any client passed to it. Clients must implement an interface that exposes a setter method that accepts the dependency.