Spring Required Annotation

The @Required annotation applies to bean property setter methods and it indicates that the affected bean property must be populated in XML configuration file at configuration time otherwise the container throws a BeanInitializationException exception. Below is an example to show the use of @Required annotation.

Example:

Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:

Step	Description
1	Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project.
2	Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3	Create Java classes Student and MainApp under the com.tutorialspoint package.
4	Create Beans configuration file Beans.xml under the src folder.
5	The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

Here is the content of Student.java file:

package com.tecra;

import org.springframework.beans.factory.annotation.Required;

public class Student {
   private Integer age;
   private String name;

   @Required
   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      return age;
   }

   @Required
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
}

Following is the content of the MainApp.java file:

package com.tecra;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = 
             new ClassPathXmlApplicationContext("Beans.xml");

      Student student = (Student) context.getBean("student");

      System.out.println("Name : " + student.getName() );
      System.out.println("Age : " + student.getAge() );
   }
}

Following is the content of the configuration file Beans.xml:

<?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-3.0.xsd">

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.tutorialspoint.Student">
      <property name="name"  value="Zara" />

      <!-- try without passing age and check the result -->
      <!-- property name="age"  value="11"-->
   </bean>

</beans>

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will raise BeanInitializationException exception and print the following error along with other log messages:

Property 'age' is required for bean 'student'

Next, you can try above example after removing comment from 'age' property 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-3.0.xsd">

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.tutorialspoint.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>
   </bean>

</beans>

Now above example will produce following result:

Name : Zara
Age : 11

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