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.tuts.heomi.netmon;
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.tuts.heomi.netmon.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.tuts.heomi.netmon.Customer" /> <bean id="personA" class="com.tuts.heomi.netmon.Person" > <property name="name" value="favtutsA" /> </bean> <bean id="personB" class="com.tuts.heomi.netmon.Person" > <property name="name" value="favtutsB" /> </bean> </beans>
When you run above example, it hits below exception :
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException:
No unique bean of type [com.tuts.heomi.netmon.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.tuts.heomi.netmon;
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=favtutsA]]Download Source Code
$ git clone https://github.com/favtuts/java-spring-tutorials.git
$ cd SpringAutoWiringQualifier