Spring Auto-Wiring Beans with @Autowired annotation

Ref:-  http://www.mkyong.com/spring/spring-auto-wiring-beans-with-autowired-annotation/


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.

Note
The @Autowired annotation is auto wire the bean by matching data type.

1. Beans
A customer bean, and declared in bean configuration file. Later, you will use “@Autowired” to auto wire a person bean.

package com.mkyong.common;

public class Customer 
{
 //you want autowired this field.
 private Person person;
 
 private int type;
 private String action;
 
 //getter and setter method
 
}



<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 id="CustomerBean" class="com.mkyong.common.Customer">
  <property name="action" value="buy" />
  <property name="type" value="1" />
 </bean>

 <bean id="PersonBean" class="com.mkyong.common.Person">
  <property name="name" value="mkyong" />
  <property name="address" value="address 123" />
  <property name="age" value="28" />
 </bean>
 
</beans>






2. Register AutowiredAnnotationBeanPostProcessor
To enable @Autowired, you have to register ‘AutowiredAnnotationBeanPostProcessor‘, and you can do it in two ways :


1. Include <context:annotation-config />
Add Spring context and <context:annotation-config /> in bean configuration file.

<beans 
 //...
 xmlns:context="http://www.springframework.org/schema/context"
 //...
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context-2.5.xsd">
 //...

 <context:annotation-config />
 //...
</beans>

Full example,

<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-2.5.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context-2.5.xsd">

 <context:annotation-config />

 <bean id="CustomerBean" class="com.mkyong.common.Customer">
  <property name="action" value="buy" />
  <property name="type" value="1" />
 </bean>

 <bean id="PersonBean" class="com.mkyong.common.Person">
  <property name="name" value="mkyong" />
  <property name="address" value="address ABC" />
  <property name="age" value="29" />
 </bean>
 
</beans>


2. Include AutowiredAnnotationBeanPostProcessor
Include ‘AutowiredAnnotationBeanPostProcessor’ directly in bean configuration file.

<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="CustomerBean" class="com.mkyong.common.Customer">
  <property name="action" value="buy" />
  <property name="type" value="1" />
 </bean>

 <bean id="PersonBean" class="com.mkyong.common.Person">
  <property name="name" value="mkyong" />
  <property name="address" value="address ABC" />
  <property name="age" value="29" />
 </bean>
 
</beans>










3. @Autowired Examples
Now, you can autowired bean via @Autowired, and it can be applied on setter method, constructor or a field.


1. @Autowired setter method
package com.mkyong.common;

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

public class Customer 
{
 private Person person;
 private int type;
 private String action;
 //getter and setter methods
 
 @Autowired
 public void setPerson(Person person) {
  this.person = person;
 }
}


2. @Autowired construtor
package com.mkyong.common;

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

public class Customer 
{
 private Person person;
 private int type;
 private String action;
 //getter and setter methods
 
 @Autowired
 public Customer(Person person) {
  this.person = person;
 }
}


3. @Autowired field
package com.mkyong.common;

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

public class Customer 
{
 @Autowired
 private Person person;
 private int type;
 private String action;
 //getter and setter methods
}



The above example will autowired ‘PersonBean’ into Customer’s person property.



Run it

package com.mkyong.common;

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

public class App 
{
    public static void main( String[] args )
    {
     ApplicationContext context = 
       new ClassPathXmlApplicationContext(new String[] {"SpringBeans.xml"});
     
     Customer cust = (Customer)context.getBean("CustomerBean");
     System.out.println(cust);
     
    }
}

Output

Customer [action=buy, type=1, 
person=Person [address=address 123, age=28, name=mkyong]]