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

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.