In this chapter, we learned about DI, which is the key feature of Spring Framework. DI helps us to make our code loosely coupled and testable. We learned various DI patterns, including constructor-setter-and field-based. We can use any of the DI patterns in our application based on our requirement, as each type has its own advantages and disadvantages.

We also learned how we can configure DI explicitly and implicitly. We can inject dependency explicitly with the use of XML-based and Java-based configuration. Annotation is used to inject dependency implicitly. Spring provides us with a special type of annotation called stereotype annotation. Spring will automatically register the class which annotated with stereotypes annotation. This makes the class available for DI in other classes and this become vital to building out our applications.

In the next chapter, we will be looking at the Spring AOP module. AOP is a powerful programming model that helps us to implement the reusable code.