About DI of Spring ①

Purpose of this article

DI: What is Dependency Injection? Continued Explanation of how Spring realizes DI

Scope of this article

Outline explanation of DI in Spring

DI review

--Reason for using DI ... I want to reduce the dependency between classes and improve reusability / testability. --How to realize ... Pass the class you want to use in a certain class with the interface type → Define the class to be actually passed separately.

DI概略.jpg

Character

--Bean ... Injection class --Bean definition ... Various properties set in the bean when injecting the bean --Bean definition file / Configuration ... A collection of Bean definitions (Java class, XML file) --DI container ... Set various beans and pass them to the other party when using them.

Outline of DI realization in Spring

Next time, detailed movements of each class ApplicationContext -** The central figure in realizing DI in Java ** --A class that has the function of a DI container --A class created by extending the BeanFactory class --There is a class that is further extended by the corresponding Configuration etc. --Multiple DI containers can be created for one application

Configuration --The Bean definition file --Pass this to the ApplicationContext class and generate a bean in the DI container -There are three methods: [Java-based], [xml-based], and [annotation-based]. ――Three can be used alone, but setting becomes easier by using the annotation base and others in combination. --Write the Bean definition in this

Bean --General class, basically no special description is required If --is an annotation-based Configuration, write an annotation separately. --You can also inject and nest beans inside the bean

ex) Describe the initialization condition for the bean of HogeService in hogeConfig and get the bean via ApplicationContext (Java base)

`CreateContext.java`


ApplicationContext ctx = new AnnotationConfigApplicationContext(HogeConfig.class);
HogeService service = ctx.getBean(HogeService.class)

`HogeConfig.java`


@Configuration
public class HogeConfig {
	@Bean
	HogeService hogeService() {
		return new HogeService(); 
	}
}

Is it like the following when expressed in a conceptual diagram? SpringにおけるDIの概要.jpg

I think it's relatively easy to understand if you swallow the concept.

Next time preview

We are planning to explain the specifications etc. when actually trying it.