In an MVC application, where will dependency injection be done?

Question

When using Spring and Spring MVC, where are dependency injection (DI)?

An example is if you have a controller and many actions in the controller.

You would do:

@RequestMapping("/blah") public String SomeAction() { ApplicationContext ctx = new AnnotationConfigApplicationContext(); MyService myService = ctx.getBean("myService"); // do something here return "someView"; } 

Would this be a best practice approach? Or is this their best way?

Answer 1

The whole idea of ​​Injection Dependency is not to let your classes know or care about how they get the objects they depend on. When injected, these dependencies should simply “appear” without any request (hence the inversion of control). When using ApplicationContext#getBean(String) you are still requesting a dependency (a la Service Locator), and this is not an inverse of the control (even if this makes it easy to change the implementation).

So, instead, you should make MyController a Spring a managed bean and insert a MyService using either installation or constructor-based installation.

 public class MyController { private MyService myService; public MyController(MyService aService) { // constructor based injection this.myService = aService; } public void setMyService(MySerice aService) { // setter based injection this.myService = aService; } @Autowired public void setMyService(MyService aService) { // autowired by Spring this.myService = aService; } @RequestMapping("/blah") public String someAction() { // do something here myService.foo(); return "someView"; } } 

And configure Spring to connect.

Answer 2

Do not use getbean, which loses the goal of doing DI. Use @Autowired instead. DI is intended for use in a multi-level system, such as view, service, DAO , so that each layer is independent of each other.

Answer 3

As a compliment to the Pascal post, Martin Fowler: Requires inversion of control containers and dependency injection pattern .

And as a comet said, you need to use the @Autowire annotation for this. In addition to this, Spring supports attachments based on name and type. I suggest you read about it.