spring @Autowire property vs setter

Question

What is the difference between anotate @Autowired to a property or do it in the setter?

As far as I know they both have the same result, but is there any reason to use o

Answer 1

There are 3 types of autowiring:

• Property based

@Autowired
private MyService service;

• Constructor based. Note in Spring Boot you don't even need @Autowired annotation in this case:

class MyController {
 private final MyService service;

 public MyController(MyService service) {
  this.service = service;
 }
}

• Setter based:

private MyService service;


@Autowired
public void setService(MyService service) {
 this.service = service;
}

It is recommended to use Constructor based, then if not possible, Setter based and lastly Property based.

Why?

• First, because in Constructor based you don't even use any Spring annotations. This helps you transition to different frameworks.

• Second, Constructor or Setter based, make unit testing much easier. You don't need to use any Spring specific testing tools and you can only use Junit and Mockito.

• Third, Constructor based is good because you can declare the property as final and not expose setters which helps with immutability and thread safety of the class.