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Another way to tell Spring which implementation to inject is to use @Qualifier Annotation.
@Qualifier is used by using
● @Service(name = "implementation1") to give a name to the Spring Component
● @Autowired @Qualifier("implementation1") to reference that Spring Component where it needs to be injected
@Primary and @Qualifier Annotations can be used at the same time.
If @Autowired Annotation doesn't specify @Qualifier, @Primary Implementation will be used.
Application Schema [Results]
Spring Boot Starters
GROUP
DEPENDENCY
DESCRIPTION
Web
Spring Web
Enables @Controller and @RequestMapping. Includes Tomcat Server.
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Create Project: springboot_autowired_qualifier (add Spring Boot Starters from the table)
Create Package: controllers (inside main package)
– Create Class: MyController.java (inside package controllers)
Create Package: services (inside main package)
– Create Interface: MyServiceInterface.java (inside package controllers)
– Create Class: MyServiceImplementation1.java (inside package controllers)
– Create Class: MyServiceImplementation2.java (inside package controllers)
MyController
@Qualifier("impl1")
http://localhost:8080/Hello
Tomcat
hello()
Browser
MyServiceInterface
@Service("impl1")
MyServiceImpl...1
@Service("impl2")
MyServiceImpl...2
MyServiceInterface.java
package com.ivoronline.springboot_autowired_qualifier.services;
public interface MyServiceInterface {
public String sayHello();
}
MyServiceImplementation1.java
package com.ivoronline.springboot_autowired_qualifier.services;
import org.springframework.stereotype.Service;
@Service("impl1")
public class MyServiceImplementation1 implements MyServiceInterface {
public String sayHello() {
return "Hello";
}
}
MyServiceImplementation2.java
package com.ivoronline.springboot_autowired_qualifier.services;
import org.springframework.stereotype.Service;
@Service("impl2")
public class MyServiceImplementation2 implements MyServiceInterface {
public String sayHello() {
return "Hello World";
}
}
MyController.java
package com.ivoronline.springboot_autowired_qualifier.controllers;
import com.ivoronline.springboot_autowired_qualifier.services.MyServiceInterface;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class MyController {
@Autowired
@Qualifier("impl1")
MyServiceInterface myService;
@ResponseBody
@RequestMapping("/Hello")
public String hello() {
String Results = myService.sayHello();
return Results;
}
}
