Categories: Spring CoreSpring FrameworkTutorial

@Required Annotation in Spring

The @Required annotation is used to specify that the value of a bean property is required to be dependency injected. That means, an error is caused if a value is not specified for that property.
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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.

Simply apply the @Required annotation will not enforce the property checking, you have to register an RequiredAnnotationBeanPostProcessor to aware of the @Required annotation in bean configuration file. Simply applying @Required annotion is not enough to enforce the property checking, you also have to register RequiredAnnotationBeanPostProcessor in bean configuration file to do so. This configuration is done in two ways one by Include and another way is Include RequiredAnnotationBeanPostProcessor in bean configuration file. which is shown in this example’s spring.xml file.

In this example Circle class has the center property as required field declare with the @Required annotation. The @Required when written on top of setCenter() method it make sure that center property must    have    be    set    else   it   will   give   compile time error message that org.springframework.beans.factory.BeanInitializationException: Property ‘center ‘ is required for bean ‘circle’ which is clearly shown in this example.

Circle.java

package com.dineshonjava.sdnext.annotation.tutorial;

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

public class Circle
{
 private Point center;

 /**
  * @param center the center to set
         * Here center is the required property for circle
  */
 @Required
 public void setCenter(Point center) 
 {
     this.center = center;
 }

 public void draw() 
 {
System.out.println("Circle is drawn of center ("+center.getX()+", "+center.getY()+")");
 }
}


Point.java

package com.dineshonjava.sdnext.annotation.tutorial;

public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
  return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
  this.y = y;
 }
}


DrawingApp.java

package com.dineshonjava.sdnext.annotation.tutorial;

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

/**
 * @author Dinesh Rajput
 *
 */
public class DrawingApp
{
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Circle circle = (Circle) context.getBean("circle");
circle.draw();
 }
}

spring.xml

<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p" xmlns:>


If we are using the element <context:annotation-config/> then there are no need to add the bean org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcess



<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcess"></bean>



Actually element <context:annotation-config/> add all the beans AnnotationBeanPostProcess included in the spring container. there are no need to add individually for @required, @autowired etc.



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:





Output:


Jul 10, 2012 5:04:09 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh


INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@758fc9: startup date [Tue Jul 10 17:04:09 IST 2012]; root of context hierarchy


Jul 10, 2012 5:04:09 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions


INFO: Loading XML bean definitions from class path resource [spring.xml]


Jul 10, 2012 5:04:10 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons


INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@19b5393: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,circle,center,org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor#0,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy


Jul 10, 2012 5:04:10 PM org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons


INFO: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@19b5393: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,circle,center,org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor#0,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy


Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circle' defined in class path resource [spring.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'center' is required for bean 'circle'

at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:527)


at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)


at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)


at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)


at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)


at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)


at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:609)


at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918)


at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:469)


at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:139)
  at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:83)
  at com.sdnext.annotation.tutorial.DrawingApp.main(DrawingApp.java:19)
 Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'center' is required for bean 'circle'

at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:149)
  at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106)
  at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
  ... 11 more




Next, we can try above example after removing comment from 'center' property as follows:



 spring.xml


<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p" xmlns:>



 Now above example will produce following result:








Output:


Jul 10, 2012 5:38:54 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh


INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Tue Jul 10 17:38:54 IST 2012]; root of context hierarchy


Jul 10, 2012 5:38:54 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions


INFO: Loading XML bean definitions from class path resource [spring.xml]


Jul 10, 2012 5:38:54 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons


INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@19b5393: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,circle,center,org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor#0,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy


Circle is drawn of center (10, 10)

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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12 years ago

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