Spring Autowiring @Qualifier example

In Spring, @Qualifier means, which bean is qualify to autowired on a field. See following scenario :

Autowiring Example

See below example, it will autowired a “person” bean into customer’s person property.

package com.mkyong.common;

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

public class Customer {

	@Autowired
	private Person person;
	//...
}

But, two similar beans “com.mkyong.common.Person” are declared in bean configuration file. Will Spring know which person bean should autowired?

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

<bean 
class ="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>
	
	<bean id="customer" class="com.mkyong.common.Customer" />
		
	<bean id="personA" class="com.mkyong.common.Person" >
		<property name="name" value="mkyongA" />
	</bean>
	
	<bean id="personB" class="com.mkyong.common.Person" >
		<property name="name" value="mkyongB" />
	</bean>

</beans>

When you run above example, it hits below exception :

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: 
	No unique bean of type [com.mkyong.common.Person] is defined: 
		expected single matching bean but found 2: [personA, personB]

@Qualifier Example

To fix above problem, you need @Quanlifier to tell Spring about which bean should autowired.

package com.mkyong.common;

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

public class Customer {

	@Autowired
	@Qualifier("personA")
	private Person person;
	//...
}

In this case, bean “personA” is autowired.

Customer [person=Person [name=mkyongA]]