Fundamentals

Dependency Injection and IOC

DI is a design pattern. Spring handles creation and linking dependencies. Constructors and setters to link dependencies.

Advantages

Having a loosely coupled systems. Easy use of mocked objects. Easily testable application. Separates the framework API and dependant objects. Reusability and readable objects.

IOC in Java

XML and Java (@Configuration) DI.

Annotations: @Autowired, @Quialifier, @Component

application-context.xml (ClassPathXmlApplicationContext.class) in src/main/resources

XML Configuration

Example setter injection:

Example constructor injection:

Java Configuration

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Bean

Java class defined in XML file.

@Qualifier when using a specific imlementacion of an interface.

Into XML fiile: <bean...>

Interfaces

They are contracts. No need to know implementation. Template based programming design approach.