@Qualifier is one of the autowiring annotations in spring.
Sometimes, it may happen that there are two or more beans, each of which equally qualifies to be wired into a property or a parameter. In such cases, Spring does not decide which one is the right one, instead, it may throw NoUniqueBeanDefinitionException. In this case, @Qualifier annotation will control which bean should be wired on a property.
In order to resolve the exception, we can use @Qualifier
annotation along with the autowiring annotation.
Here is the complete example, of @Qualifier
annotation usage.
Spring @Qualifier annotation:
Project Structure :
Required Dependencies :
pom.xml
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring-framework.version}</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>${slf4j.version}</version>
<scope>compile</scope>
</dependency>
</dependencies>
Spring Beans :
College.java
package com.onlinetutorialspoint.beans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
public class College {
private int collegeId;
private String collegeName;
@Autowired
@Qualifier("cse")
private Department department;
public int getCollegeId() {
return collegeId;
}
public void setCollegeId(int collegeId) {
this.collegeId = collegeId;
}
public String getCollegeName() {
return collegeName;
}
public void setCollegeName(String collegeName) {
this.collegeName = collegeName;
}
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
}
Department.java
package com.onlinetutorialspoint.beans;
public class Department {
private int deptId;
private String deptName;
public int getDeptId() {
return deptId;
}
public void setDeptId(int deptId) {
this.deptId = deptId;
}
public String getDeptName() {
return deptName;
}
public void setDeptName(String deptName) {
this.deptName = deptName;
}
}
spring configuration:
spring configuration.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
<context:component-scan base-package="com.onlinetutorialspoint.beans" />
<context:annotation-config />
<bean id="college" class="com.onlinetutorialspoint.beans.College">
<property name="collegeId" value="10059" />
<property name="CollegeName" value="CBIT" />
</bean>
<bean id="cse" class="com.onlinetutorialspoint.beans.Department">
<property name="deptName" value="CSE" />
<property name="deptId" value="101" />
</bean>
<bean id="it" class="com.onlinetutorialspoint.beans.Department">
<property name="deptName" value="INFORMATION TECHNOLOGY" />
<property name="deptId" value="102" />
</bean>
<bean id="mechanical" class="com.onlinetutorialspoint.beans.Department">
<property name="deptName" value="Mechanical" />
<property name="deptId" value="103" />
</bean>
</beans>
On the above configuration file, we took 3 different Department beans with different ids. To avoid ambiguity, while injecting the dependency of Department bean we can use @Qualifier annotation on top of the property.
Run the application:
Main.java
package com.onlinetutorialspoint.beans;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
BeanFactory beanFactory = new ClassPathXmlApplicationContext("springconfiguration.xml");
College college = (College) beanFactory.getBean("college");
Department department = college.getDepartment();
System.out.println("College Name : "+college.getCollegeName());
System.out.println("Department Id : "+department.getDeptId());
System.out.println("Department Name : "+department.getDeptName());
}
}
Output :
College Name : CBIT
Department Id : 101
Department Name : CSE
Happy Learning 🙂