The @Required annotation is applied to bean property-setter functions. The bean property must be populated in the XML configuration file at configuration-time. This annotation essentially shows that the setter function must be arranged to be dependency-injected with a value at configuration-time.

Add a user model and the Main class with a bean.xml configuration file.

The content of the bean.xml configuration file is as follows:

<?xml version = "1.0" encoding = "UTF-8"?>
<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-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context.xsd">

    <context:annotation-config/>  <!--after this tag, we have to write the beans-->

    <bean id="users" class="requiredAnnotation.UsersForReq">
        <property name="name" value="Naruto Uzumaki"/>
        <property name="village" value="Konohagakure"/>
    </bean>
</beans>

The content of UsersForReq.kt is as follows:

class Users{
    private var village: String? = null
    private var name: String? = null

    @Required
    fun setVillage(village: String?) {
        this.village = village
    }

    fun getVillage(): String? {
        return village
    }

    @Required
    fun setName(name: String) {
        this.name = name
    }

    fun getName(): String? {
        return name
    }
}

The content of AnnotationBasedReqApp.kt is as follows:

fun main(args: Array<String>) {
    val context = ClassPathXmlApplicationContext("requiredAnnotation/beans_for_req.xml")
    val users = context.getBean("users") as UsersForReq

    println("Name: "+users.getName())
    println("Village: "+users.getVillage())
}

The output of this project will be as follows:

Name: Naruto Uzumaki
Village: Konohagakure