CODEWITHSUNDEEP
javaspringspring-mvcdependency-injectioninversion-of-control
ssal
ssal

Reputation: 87

How are IoC and DI used in Spring MVC

I’m taking this udemy course all about Spring Hibernate etc. The course started with explaining how Injection of Control and dependency injection works not in a web perspective just like having simple classes or beans, defining beans and their dependencies inside a config xml file or inside the actual class Using java annotation and then a main class where the beans are created. I understood that despite not really seeing the big benefit of using IoC and DI other than separating roles like creating and maintaining objects and adding dependencies the object needs and I guess when the project is bigger this makes it cleaner and easier to follow right?

However what I don’t understand is how IOC and DI ties in a full spring MVC project. Like I understand using the @Controller annotation means it’s like an @Component and you could make it scan the components automatically when it creates beans but like unlike before there isn’t a main class where beans are created and configured rather I have a controller class where I manually create objects and models and pass that back to the views where I can use the values in the model. I don’t see how I use IoC or DI here? Or is it because it’s a simple project and perhaps the objects we created didn’t have many dependencies?Or are a lot of the uses and implementation done internally or automatically?

I am just struggling to a) see why IoC and DI are that important and b) how are they actually used in a Spring MVC project where you don’t have a main class where you do create beans.

Upvotes: 1

Views: 1009

Answers (2)

Maddy
Maddy

Reputation: 91

IoC is a process whereby objects define their dependencies, that is, the other objects they work with, only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects those dependencies when it creates the bean. This process is fundamentally the inverse, hence the name Inversion of Control (IoC), of the bean itself controlling the instantiation or location of its dependencies by using direct construction of classes, or a mechanism such as the Service Locator pattern.

In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application.

The advantages of this architecture are:

  • decoupling the execution of a task from its implementation
  • making it easier to switch between different implementations
  • greater modularity of a program
  • greater ease in testing a program by isolating a component or mocking its dependencies and allowing components to communicate through contracts

Inversion of Control can be achieved through various mechanisms such as: Strategy design pattern, Service Locator pattern, Factory pattern, and Dependency Injection (DI).

You can go with Annotation based configuration, where you can define @Configuration class and return the required beans using @Bean annotation. Also you can use @Component to your POJO class to treat it as Spring bean.

Upvotes: 1

Rashed
Rashed

Reputation: 144

A) Create a project, but don't add any dependency (or web-mvc). Then do it yourself then see how much need time to create configure manually. If it is just a simple mvc project, you can do it manually, but if your project increase day by day then a huge configuration file to maintain your project properly. But when you are professional developer, you don't have so much time to configure all those manually. So here is come the solution IoC and DI. Controller or other anotation are configured in build-in jars. You don't have to worried about to create controller or to create bean, just use them when you neer them. It's save your time as well as headache about is it working or not. It's increase your productivity while your are working on a big project.

B) Yes, there is no main class in web project. To run a web project, you need a server. The server first looking for a configuration (In spring, it's web.xml, dispatcher-servlet). If it available then expand the configuration file, if not then throw an error. In that configuration file, explain everything about the web project. What should do, what is not mandatory, what is entry point etc.

So, IoC and DI are very important because to understand how a web project work behind the scene or how all component work together.

Upvotes: 1

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