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]]