@Autowired Annotation (Part2)

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1) @Autowired on Setter methods

Following example shows how to use @Autowired on Setter methods.

Student.java

package examples.springanno;

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

public class Student {

    private String name;
    private String address;
    private Course course;
   
 
    public void setName(String name){
        this.name = name;
       
    }
    public String getName(){
        return name;
    }
   
    public void setAddress(String address){
        this.address = address;
       
    }
    public String getAddress(){
        return address;
    }
   
    @Autowired
    public void setCourse(Course c){
        this.course = c;
       
    }
    public Course getCourse(){
        return course;
    }
   
    public void displayInfo(){
        System.out.println("Student name     : "+name);
        System.out.println("Student Address : "+address);
        System.out.println("    Course Details:");
        System.out.println("    Course Name :    "+this.course.getCourseName());
    }
}

Course.java

package examples.springanno;

public class Course {

String courseName;

public void setCourseName(String courseName){
    this.courseName = courseName;
   
}
public String getCourseName(){
    return courseName;
}

}

ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="https://www.springframework.org/schema/beans" 
xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
xmlns:context="https://www.springframework.org/schema/context"
xsi:schemaLocation="https://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans-3.0.xsd
https://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context-3.0.xsd
">

<!-- Enabling Spring to use @Autowired-->
<context:annotation-config/>

<bean id="student" class="examples.springanno.Student" >

<property name="name" value="abc"/>
<property name="address" value="xyz"/>

<!-- No need to write following line.This property will be automatically  injected using @Autowired.

<property name="course" ref="course"/>
-->

</bean>

<bean id="course" class="examples.springanno.Course">
<property name="courseName" value="Computer Applications"/>
</bean>


</beans>

MainApp.java

package examples.springanno;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String args[]){
        ApplicationContext ctx=new ClassPathXmlApplicationContext("resources/ApplicationContext.xml");
        Student student = (Student)ctx.getBean("student");
        student.displayInfo();       
    }

}

Output:

Student name     : abc
Student Address : xyz
    Course Details:
    Course Name :    Computer Applications

Note that in above code (in ApplicationContext.xml) we are providing values of only two fields of Student class namely - name and address. We are not providing value for third field - course. The value of this third field i.e course will be injected using @Autowired because we have annotated its setter method with @Autowired in the Student class.

@Autowired does [by type autowiring]. It will search configuration file for a bean whose type is same as that corresponding property on which @Autowired has been applied. If such matching bean found then it will inject it's reference to that property as its value.

Since our field course is of type Course, @Autowired will search xml configuration file for a bean which is of type Course and then inject its reference as value for third field of Student class.

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