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<div style="color: #274e13;">The <b>@Required</b> 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. </div>
<div style="color: #274e13;">
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<div style="color: #274e13;">The <b>@Required</b> annotation applies to bean <b>property setter methods</b> and it indicates that the affected bean property must be populated in XML configuration file at configuration time otherwise the container throws a <b>BeanInitializationException </b>exception. Below is an example to show the use of <b>@Required</b> annotation.</p>
<p>Simply apply the <b>@Required</b> annotation will not enforce the property checking, you have to register an <b>RequiredAnnotationBeanPostProcessor </b>to aware of the <b>@Required</b> annotation in bean configuration file. Simply applying <b>@Required</b> annotion is not enough to enforce the property checking, you also have to register <b>RequiredAnnotationBeanPostProcessor </b>in bean configuration file to do so. This configuration is done in two ways one by Include and another way is Include <b>RequiredAnnotationBeanPostProcessor </b>in bean configuration file. which is shown in this example&#8217;s <b>spring.xml</b> file.</p>
<p>
In<b> </b>this example <b>Circle </b>class has the <b>center </b>property as required field declare with the <b>@Required </b>annotation. The <b>@Required</b> when written on top of <b>setCenter()</b> method it make sure that <b>center </b>property must  ; ; have  ; ; be  ; ; set ; ; ; else ; ; it ; ; will ; ; give ; ; compile time error message that <b>org.springframework.beans.factory.BeanInitializationException: Property &#8216;center &#8216; is required for bean &#8216;circle&#8217; </b>which is clearly shown in this example.</p>
</div>
<p><b>Circle.java</b></p>
<pre class="highlight" name="code">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()+")");
 }
}
</pre>
<p><b><br />
</b> <b>Point.java</b></p>
<pre class="highlight" name="code">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;
 }
}
</pre>
<p><b><br />
</b> <b>DrawingApp.java</b></p>
<pre class="highlight" name="code">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();
 }
}

</pre>
<p><b>spring.xml</b></p>
<pre class="highlight" name="code"><;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:><div style="color: #274e13;"><br />
If we are using the element <b><;context:annotation-config/>;</b> then there are no need to add the bean <b>org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcess</b></div><br />
<pre class="highlight" name="code"><;bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcess">;<;/bean>;
</pre>
<div style="color: #274e13;">Actually element <b><;context:annotation-config/>;</b> add all the beans <b>AnnotationBeanPostProcess</b> included in the <a href="https://dineshonjava.com/2012/06/spring-ioc-container.html">spring container</a>. there are no need to add individually for <b>@required, @autowired</b> etc.</p>
</div>
<div style="color: #274e13;">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 <b>BeanInitializationException </b>exception and print the following error along with other log messages:</p>
</div>
<div style="background-color: #ff99cc; border-width: thin; border: solid;">
<div style="color: blue;"><b>Output:</b></div>
<div style="color: red;">Jul 10, 2012 5:04:09 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh</div>
<div style="color: red;">INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@758fc9: startup date [Tue Jul 10 17:04:09 IST 2012]; root of context hierarchy</div>
<div style="color: red;">Jul 10, 2012 5:04:09 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions</div>
<div style="color: red;">INFO: Loading XML bean definitions from class path resource [spring.xml]</div>
<div style="color: red;">Jul 10, 2012 5:04:10 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons</div>
<div style="color: red;">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$ImportAwareBeanPostProcessor#0]; root of factory hierarchy</div>
<div style="color: red;">Jul 10, 2012 5:04:10 PM org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons</div>
<div style="color: red;">INFO: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@19b5393: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,circle,center,org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor#0,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy</div>
<p>Exception in thread "main" <u style="color: blue;">org.springframework.beans.factory.BeanCreationException:</u> Error creating bean with name 'circle' defined in class path resource [spring.xml]: Initialization of bean failed; nested exception is <u style="color: blue;">org.springframework.beans.factory.BeanInitializationException:</u> <b>Property 'center' is required for bean 'circle'</b><br />
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:527)</p>
<div style="color: red;">at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)</div>
<div style="color: red;">at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)</div>
<div style="color: red;">at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)</div>
<div style="color: red;">at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)</div>
<div style="color: red;">at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)</div>
<p>at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:609)</p>
<div style="color: red;">at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918)</div>
<div style="color: red;">at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:469)</div>
<p>at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:139)<br style="color: red;" /> at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:83)<br style="color: red;" /> at com.sdnext.annotation.tutorial.DrawingApp.main(DrawingApp.java:19)<br style="color: red;" /> Caused by: <u style="color: blue;">org.springframework.beans.factory.BeanInitializationException:</u> <b>Property 'center' is required for bean 'circle'</b><br />
at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:149)<br style="color: red;" /> at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106)<br style="color: red;" /> at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)<br style="color: red;" /> ... 11 more
</div>
<p>
Next, we can try above example after removing comment from 'center' property as follows:<br />
<b><br />
</b> <b>spring.xml</b></p>
<pre class="highlight" name="code"><;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:></p>
<div style="color: #274e13;"><b><br />
</b> <b>Now above example will produce following result:</b><br />
<b><br />
</b></div>
<div style="background-color: #ff99cc; border-width: thin; border: solid;">
<div style="color: blue;"><b>Output:</b></div>
<div style="color: red;">Jul 10, 2012 5:38:54 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh</div>
<div style="color: red;">INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Tue Jul 10 17:38:54 IST 2012]; root of context hierarchy</div>
<div style="color: red;">Jul 10, 2012 5:38:54 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions</div>
<div style="color: red;">INFO: Loading XML bean definitions from class path resource [spring.xml]</div>
<div style="color: red;">Jul 10, 2012 5:38:54 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons</div>
<div style="color: red;">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</div>
<p><b>Circle is drawn of center (10, 10)</b></div>
</div>
<p></p>
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