[JAVA] How to set Dependency Injection (DI) for Spring Boot

We have summarized how to set Dependency Injection for Spring Framework.

Specifying the scan target of the component

By default, packages in the same hierarchy as the package of the class with @ComponentScan are scanned. If you want to scan other classes, specify the package name in scanBasePackage.

// @It can also be specified in compound annotations such as SpringBootApplication.

Dependency injection (DI) settings

When using Spring annotation

Define the dependent object as a member of private`` final, and define the constructor that receives the dependent object as an argument in the constructor. When using Lombok, it can be described as follows.

Component definition
class ComponentA { ...
DI settings
class ClassA {
	// @Autowired can be omitted.
	private final ComponentA componentA;

Previously, it was mainstream to specify @Autowired for non-final members or their Setters.

class ClassA {
    private ComponentA componentA;
class ClassA {
	private ComponentA componentA;
	public void setComponentA(ComponentA componenA) {

This is currently recommended because using the constructor has the following advantages:

--Become a module that can be used without DI. (The dependency can be set in the constructor on the user side.) --You can add the final qualifier. (The variable that stores the DI object is not usually rewritten.)

When using JSR-330 annotation

Since it is a Java standard, it is easy to switch to another DI container.

Component definition
@Named //[email protected]
class ComponentA { ... }
DI settings

Specify @Inject in the constructor (or Setter). (Setter is also acceptable.)

class ClassA {
	private final ComponentA componentA;

Alternatively, specify @Inject as a member.

class ClassA {
	private ComponentA componentA;


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