Define custom @Required-style annotation in Spring

The @Required annotation is used to make sure a particular property has been set. If you are migrate your existing project to Spring framework or have your own @Required-style annotation for whatever reasons, Spring is allow you to define your custom @Required-style annotation, which is equivalent to @Required annotation.
In this example, you will create a custom @Required-style annotation named @Mandatory, which is equivalent to @Required annotation.

1. Create the @Mandatory interface

package com.mkyong.common;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Mandatory {
}

2. Apply it to a property

package com.mkyong.common;

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

3. Register it

Include your new @Mandatory annotation in ‘RequiredAnnotationBeanPostProcessor’ class.

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

4. Done

Done, you just created a new custom @Required-style annotation named @Mandatory, which is equivalent to @Required annotation.