如何在无参数构造函数中访问Spring bean？

Question

@Component
public class MyClass {
    public MyClass() {
        SomeInterface something;

        // Spring magic that i don't know

        something.toString();
    }
}

What Spring magic do I need to use to inject a bean into "something"?

I also wouldn't mind if it was a field. It just has to be usable from within the constructor!

Answer 1

The basic rules also apply to Spring:

• to construct an object, Spring needs to invoke the constructor
• Spring can't call a method of an object or set one of its fields if it isn't constructed yet
• so if you want to access a field set by Spring , you can't do that from the constructor, unless the value is passed as argument to the constructor.

This thus leaves two choices:

1. constructor injection:

    @Autowired public MyClass(SomeInterface something) { // use something } 

2. post-construct method, called after all the injections have been done, whatever the way:

    @Autowired private SomeInterface something; @PostConstruct private void initialize() { // use something }