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 {@Autowiredprivate 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/beanshttp://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]]