In last Spring auto-wiring 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.
Note
The @Autowired annotation is auto wire the bean by matching data type.
See following full example to demonstrate the use of @Autowired.
1. Beans
A customer bean, and declared in bean configuration file. Later, you will use “@Autowired” to auto wire a person bean.
package com.tuts.heomi.netmon;
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.tuts.heomi.netmon.Customer">
<property name="action" value="buy" />
<property name="type" value="1" />
</bean>
<bean id="PersonBean" class="com.tuts.heomi.netmon.Person">
<property name="name" value="favtuts" />
<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.tuts.heomi.netmon.Customer"> <property name="action" value="buy" /> <property name="type" value="1" /> </bean> <bean id="PersonBean" class="com.tuts.heomi.netmon.Person"> <property name="name" value="favtuts" /> <property name="address" value="address ABC" /> <property name="age" value="29" /> </bean> </beans>
If you are using Spring 2.5, you may face with the error: [org.springframework.context.annotation.AnnotationConfigBeanDefinitionParser] are only available on JDK 1.5 and higher .
To fix it, you need to migrate your spring version from 2.5 to >=3.2.3. For Spring migration you need to do following changes
1) In your
pom.xmlremove dependency for spring 2.5.6 and add dependency for spring new version.2) Update ‘
xsi:schemaLocation‘ in beans tag ofapplicationcontet.xmlfile of your project.e.g update http://www.springframework.org/schema/beans/spring-beans-2.5.xsd to http://www.springframework.org/schema/beans/spring-beans-3.2.xsd for spring 3.2.3 version.
3) Clean,build and re-deploy your project.
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.tuts.heomi.netmon.Customer">
<property name="action" value="buy" />
<property name="type" value="1" />
</bean>
<bean id="PersonBean" class="com.tuts.heomi.netmon.Person">
<property name="name" value="favtuts" />
<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.tuts.heomi.netmon;
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.tuts.heomi.netmon;
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.tuts.heomi.netmon;
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.tuts.heomi.netmon;
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=favtuts]]Dependency checking
By default, the @Autowired will perform the dependency checking to make sure the property has been wired properly. When Spring can’t find a matching bean to wire, it will throw an exception. To fix it, you can disable this checking feature by setting the “required” attribute of @Autowired to false.
package com.tuts.heomi.netmon;
import org.springframework.beans.factory.annotation.Autowired;
public class Customer
{
@Autowired(required=false)
private Person person;
private int type;
private String action;
//getter and setter methods
}
In the above example, if the Spring can’t find a matching bean, it will leave the person property unset.
@Qualifier
The @Qualifier annotation us used to control which bean should be autowire on a field. For example, bean configuration file with two similar person beans.
<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.tuts.heomi.netmon.Customer"> <property name="action" value="buy" /> <property name="type" value="1" /> </bean> <bean id="PersonBean1" class="com.tuts.heomi.netmon.Person"> <property name="name" value="favtuts1" /> <property name="address" value="address 1" /> <property name="age" value="28" /> </bean> <bean id="PersonBean2" class="com.tuts.heomi.netmon.Person"> <property name="name" value="favtuts2" /> <property name="address" value="address 2" /> <property name="age" value="28" /> </bean> </beans>
Will Spring know which bean should wire?
To fix it, you can use @Qualifier to auto wire a particular bean, for example,
package com.tuts.heomi.netmon;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
public class Customer
{
@Autowired
@Qualifier("PersonBean1")
private Person person;
private int type;
private String action;
//getter and setter methods
}
It means, bean “PersonBean1” is autowired into the Customer’s person property. Read this full example – Spring Autowiring @Qualifier example
Conclusion
This @Autowired annotation is highly flexible and powerful, and definitely better than “autowire” attribute in bean configuration file.
Download Source Code
$ git clone https://github.com/favtuts/java-spring-tutorials.git
$ cd SpringAutoWiringAutowired