@Autowired Annotation in Spring Example

In last Spring Bean Autowiring in Spring in XML example, it will autowired the matched property of any bean in current Spring container. In most cases, you may need autowired property in a particular bean only.

In Spring, you can use @Autowired annotation to auto wire bean on the setter method, constructor or a field. Moreover, it can autowired property in a particular bean.
Autowired Annotation in Spring Example
@ImageSource-Slideshare.net
Note:
The @Autowired annotation is auto wire the bean by matching data type if spring container find more than one beans same data type then it find by name

@Autowired on Setter Method:
You can use @Autowired annotation on setter methods to get ref id of the <property> element in XML configuration file(spring.xml). When Spring finds an @Autowired annotation used with setter methods, it tries to perform byType autowiring on the method.

See following full example to demonstrate the use of @Autowired.

Circle.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

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

public class Circle
{ 
 private Point center;
 //using autowired annotation with setter method
 @Autowired
 public void setCenter(Point center) 
 {
           this.center = center;
 }

 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}
Point.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
    return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
           this.y = y;
 }
}
DrawingApp.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

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

/**
 * @author Dinesh Rajput
 *
 */
public class DrawingApp
{
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Circle circle = (Circle) context.getBean("circle");
circle.draw();
 }
}
spring.xml
<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p" xmlns:security="http://www.springframework.org/schema/security" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans" xsi:schemalocation="http://www.springframework.org/schema/beans">
  
<bean class="com.dineshonjava.sdnext.autowiredannotation.tutorial.Circle" id="circle">
</bean>
  
<bean class="com.dineshonjava.sdnext.autowiredannotation.tutorial.Point" id="pointA">
   <property name="x" value="0"></property>
   <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.autowiredannotation.tutorial.Point" id="pointB">
   <property name="x" value="-20"></property>
   <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.autowiredannotation.tutorial.Point" id="pointC">
   <property name="x" value="20"></property>
   <property name="y" value="0"></property>
</bean> 
  
<bean class="com.dineshonjava.sdnext.autowiredannotation.tutorial.Point" id="center">
   <property name="x" value="10"></property>
   <property name="y" value="10"></property>
</bean>
  
 <!-- <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/> -->    
<!-- <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/> -->    
<context:annotation-config></context:annotation-config>
</beans>

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:

Output:
Jul 10, 2012 7:41:44 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Tue Jul 10 19:41:44 IST 2012]; root of context hierarchy
Jul 10, 2012 7:41:44 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jul 10, 2012 7:41:44 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1d80e6d: defining beans [circle,pointA,pointB,pointC,center,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy
Circle is drawn of center (10, 10)

@Autowired on Properties:
You can use @Autowired annotation on properties to get ref id of the setter methods. When you will pass values of autowired properties using Spring will automatically assign those properties with the passed values or references.
Circle.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

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

public class Circle
{ 
 //using autowired annotation with property
 @Autowired
 private Point center;
 
 public void setCenter(Point center) 
 {
     this.center = center;
 }

 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}

@Autowired on Constructors:
You can apply @Autowired to constructors as well. A constructor @Autowired annotation indicates that the constructor should be autowired when creating the bean, even if no <constructor-arg/> elements are used while configuring the bean in XML file.
Circle.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

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

public class Circle
{ 
 private Point center;
 
 //using autowired annotation with constructor
 @Autowired
 public Center(Point center) 
 {
     this.center = center;
 }

 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}

@Autowired with (required=false) option:
By default, the @Autowired annotation has the required dependency but we can set the required dependency to false as below:

Circle.java
package com.dineshonjava.sdnext.autowiredannotation.tutorial;

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

public class Circle
{ 
 //using autowired annotation with property
 @Autowired(required=false)
 private Point center;
 
 public void setCenter(Point center) 
 {
     this.center = center;
 }

 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}


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