How @Qualifier and @Primary Annotation works in Spring

How @Qualifier and @Primary Annotation works in Spring

@Qualifier and @Primary Annotation both used in auto wiring of beans

@Primary Annotation

@Primary Annotation is used to mark a spring as  default primary bean for injection candidate if  container one more bean candidate for a injection bean location.

@Qualifier  Annotation

@Qualifier  Annotation allow to identify a particular bean when more the one bean implementation found for auto wiring during  resolution time of bean object injection  by spring container .

Following code example illustrate the working these annotation 

 

Employee.java

package in.jk.spring.autowired.test;

public interface Employee {

public String toString();

}

Developer.java

package in.jk.spring.autowired.test;

public class Developer implements Employee {

@Override

public String toString() {

return "Developer Bean";

}

}

DeveloperQualifier.java

package in.jk.spring.autowired.test;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

import org.springframework.beans.factory.annotation.Qualifier;

@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })

@Retention(RetentionPolicy.RUNTIME)

@Qualifier

public @interface DeveloperQualifier {

}

Manager.java

package in.jk.spring.autowired.test;

public class Manager implements Employee {

@Override

public String toString() {

return "Manager Bean";

}

}

ManagerQualifier.java

package in.jk.spring.autowired.test;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

import org.springframework.beans.factory.annotation.Qualifier;

@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })

@Retention(RetentionPolicy.RUNTIME)

@Qualifier

public @interface ManagerQualifier {

}

BeanConfiguration.java

package in.jk.spring.autowired.test;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Primary;

@Configuration

public class SpringConfig {

@Bean

@Primary

@DeveloperQualifier()

public Employee getJavaEmp() {

return new Developer();

}

@Bean

@ManagerQualifier()

public Employee getManeger() {

return new Manager();

}

}

TestBean.java

package in.jk.spring.autowired.test;

import org.springframework.beans.factory.annotation.Autowired;

public class TestBean {

@Autowired

@DeveloperQualifier()

Employee developer;

@Autowired

@ManagerQualifier

Employee manager;

public void printEmpoyee() {

System.out.println(developer);

System.out.println(manager);

}

}

SpringApplication.java

package in.jk.spring.autowired.test;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringApplication {

public static void main(String[] args) {

ApplicationContext applicationContext = null;

applicationContext =new ClassPathXmlApplicationContext("context.xml");

SpringConfig configuration = (SpringConfig ) applicationContext.getBean("config");

TestBean testBean = (TestBean) applicationContext.getBean("testBean");

testBean.printEmpoyee();

}

}

context.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans 

    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd

    http://www.springframework.org/schema/context 

    http://www.springframework.org/schema/context/spring-context-2.5.xsd">

<context:annotation-config />

<context:component-scan

base-package="in.jk.spring.config" />

<context:property-placeholder

location="classpath:application.properties" />

<bean id="testBean" class="in.jk.spring.autowired.test.TestBean">

</bean>

<bean id="config"

class="in.jk.spring.autowired.test.SpringConfig ">

</bean>

</beans>