Where is the @Autowired annotation supposed to go - on the property or the method?

Which is more correct?

This (with the @Autowired annotation on the method)?

@Controller
public class MyController
{
private MyDao myDao;

@Autowired
public MyController(MyDao myDao)
{
this.myDao = myDao;
}

This (with the @Autowired annotation on the property)?

@Controller
public class MyController
{
@Autowired
private MyDao myDao;

public MyController(MyDao myDao)
{
this.myDao = myDao;
}

Where is the @Autowired annotation supposed to go?

The annotation goes with the property, because that's what's being autowired; the property to be automatically set. [This tutorial][1] has a nice example. [This more advanced example][2] shows how to use qualifiers to disambiguate the wiring.


[1]:

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[2]:

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According to [the Javadoc for Autowired][1], the annotation can be used on "a constructor, field, setter method or config method". See [the full documentation][2] for more details.

I personally prefer your first option (constructor injection), because the `myDao` field can be marked as final:

@Controller
public class MyControllear {
private final MyDao myDao;

@Autowired
public MyController(MyDao myDao) {
this.myDao = myDao;
}

Constructor injection also allows you to test the class in a unit test without code that depends on Spring.

The second option would be better written as:

@Controller
public class MyControllear {
@Autowired
private MyDao myDao;

MyController() {
}

With field injection, Spring will create the object, then update the fields marked for injection.

One option you didn't mention was putting `@Autowired` on a setter method (setter injection):

@Controller
public class MyControllear {
private MyDao myDao;

MyController() {
}

@Autowired
public void setMyDao(MyDao myDao) {
this.myDao = myDao;
}


You do not have to choose one or another. You can use field injection for some dependencies and constructor injection for others for the same object.


[1]:

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[2]:

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