Use Setter injection when a number of dependencies are more or you need readability. Use Constructor Injection when Object must be created with all of its dependency.

Which is better setter injection and constructor injection?

If we use both constructor and setter injection, IOC container will use the setter injection. Changes: We can easily change the value by setter injection. It doesn't create a new bean instance always like constructor. So setter injection is flexible than constructor injection.

Why is constructor injection better?

Constructor injection helps us to identify if our bean is dependent on too many other objects. If our constructor has a large number of arguments this may be a sign that our class has too many responsibilities. We may want to think about refactoring our code to better address proper separation of concerns.