Spring Auto-Wiring Beans with @Autowired annotation
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.
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.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]]
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.mkyong.common; 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.mkyong.common.Customer"> <property name="action" value="buy" /> <property name="type" value="1" /> </bean> <bean id="PersonBean1" class="com.mkyong.common.Person"> <property name="name" value="mkyong1" /> <property name="address" value="address 1" /> <property name="age" value="28" /> </bean> <bean id="PersonBean2" class="com.mkyong.common.Person"> <property name="name" value="mkyong2" /> <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.mkyong.common; 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
The application runs in JBoss 6.0.0 Final, but not in JBoss AS 7.1.1.
We get a timeout without any error message. Only the following timeout is displayed:
…
11:36:07,972 INFO [org.jboss.as.server] (DeploymentScanner-threads – 2)
JBAS015870: Deploy of deployment “AS7.ear” wasrolled back with failure message Operation cancelled
11:36:07,972 ERROR [org.jboss.as.server.deployment.scanner]
(DeploymentScanner-threads – 1) JBAS015052: Did not receive a response to the deployment operation within the allowed timeout period [60 seconds]. Check the server configuration file and the server logs to find more about the status of the deployment.
I have used @Autowired without configuring AutowiredAnnotationBeanPostProcessor or context:annotation-config and it works.
How is that possible. My spring version is 2.5.6
Thanks for this simple tutorial
I have used @Autowired without configuring AutowiredAnnotationBeanPostProcessor or and it works.
How is that possible. My spring version is 2.5.6
Thanks for this simple tutorial
I have got everything working without having AutowiredAnnotationBeanPostProcessor or
How was that possible?
I have a question. You have used:
ApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"com/mkyong/common /SpringBeans.xml"}); Customer cust = (Customer)context.getBean("CustomerBean"");To start you soring context off. Is there no way to autowire the first bean “CustomerBean”?
Thanks
Sorry caused you confused, above example is for demonstration purpose only. Sure you can autowire the “customerBean”, the concept is same with “personBean”.
How when The main method is static?
Thanks. Was helpful.
Hi great Spring by example type post. I had to place the bean configuration file into the package level that the Person and Customer class existed in order to get it to work:
I have seen other Spring examples where the author places the bean configuration xml file on the project level? Is there a convention for this? Did I forget something in order to have the bean configuration file on the project level?
Geo
Forgot one other thing. If you have a constructor with the Autowired bean in the argument you need to make sure to place the @Qualifier annotation in the argument:
And also the same for any setter you may have in the class:
Hope that helps,
Geo
Geo I think your first code example should be:
Great note. thanks.
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