Spring dependency checking with @Required Annotation
Spring’s dependency checking in bean configuration file is used to make sure all properties of a certain types (primitive, collection or object) have been set. In most scenarios, you just need to make sure a particular property has been set, but not all properties..
For this case, you need @Required
annotation, see following example :
@Required example
A Customer
object, apply @Required
in setPerson()
method to make sure the person
property has been set.
package com.mkyong.common;
import org.springframework.beans.factory.annotation.Required;
public class Customer
{
private Person person;
private int type;
private String action;
public Person getPerson() {
return person;
}
@Required
public void setPerson(Person person) {
this.person = person;
}
}
Simply apply the @Required
annotation will not enforce the property checking, you also need to register an RequiredAnnotationBeanPostProcessor
to aware of the @Required
annotation in bean configuration file.
The RequiredAnnotationBeanPostProcessor
can be enabled 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 RequiredAnnotationBeanPostProcessor
Include ‘RequiredAnnotationBeanPostProcessor
’ 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.RequiredAnnotationBeanPostProcessor"/>
<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>
If you run it , the following error message will be throw, because person
property is unset.
org.springframework.beans.factory.BeanInitializationException:
Property 'person' is required for bean 'CustomerBean'
Conclusion
Try @Required
annotation, it is more flexible than dependency checking in XML file, because it can apply to a particular property only.
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