How to use @Required Annotation in Spring?

In most cases, you would like to check if particular properties have been set, but not all properties of certain types. For this Spring provides @Required annotation in order to check a particular property. It works in Java1.5 and above versions only.

Let's use @Required annotation in  application.AccountService.java

1. package org.myjavaswtech.service;  
2.   
3. import org.myjavaswtech.dao.AccountDAO;  
4. import org.springframework.beans.factory.annotation.Required;  
5.   
6. public class AccountService {  
7.   
8.  private AccountDAO accountDao;  
9.   
10.  @Required  
11.  public void setAccountDao(AccountDAO accountDao) {  
12.   this.accountDao = accountDao;  
13.  }   
14.  public void transferFund(String acNo, String benAcNo, double amount){  
15.   System.out.println("Call to Account DAO");  
16.   accountDao.transferFund(acNo, benAcNo, amount);  
17.  }  
18. }  

Inorder to work @Required Annotation, you need to register RequiredAnnotationBeanPostProcessor instance in the IoC container.

RequiredAnnotationBeanPostProcessor is a Spring bean post processor that checks if all the bean properties with the @Required annotation have been set.

beans.xml

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1. <?xml version="1.0" encoding="UTF-8"?>  
2. <beans xmlns="http://www.springframework.org/schema/beans"  
3.  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
4.  xsi:schemaLocation="http://www.springframework.org/schema/beans   
5.  http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">  
6.  <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>  
7.    
8.  <bean name="accountDao" class="org.myjavaswtech.dao.AccountDAO">  
9.  </bean>  
10.   
11.  <bean name="accountService" class="org.myjavaswtech.service.AccountService" dependency-check="objects">  
12.   <!-- <property name="accountDao" ref="accountDao" /> -->  
13.  </bean>  
14.   
15.  <bean name="accountBean" class="org.myjavaswtech.beans.AccountBean" >  
16.   <property name="senderAcNo" value="ac123456"/>  
17.   <property name="beneficiaryAcNo" value="ac7890" />  
18.   <property name="amount" value="10000"/>  
19.   <property name="accountService" ref="accountService"/>  
20.  </bean>  
21.   
22. </beans>  

Now Run the application: You'll get the following exception

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'accountService' defined in class path resource [beans.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'accountDao' is required for bean 'accountService'.

Spring2.5 and Above : <context:annotation-config>

In Spring2.5 and above versions, <context:annotation-config> is used in IOC container instead of RequiredAnnotationBeanPostProcessor. If you use <context:annotation-config> element in your bean configuration file, and a RequiredAnnotationBeanPostProcessor instance will automatically get registered.

beans.xml

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1. <?xml version="1.0" encoding="UTF-8"?>  
2. <beans xmlns="http://www.springframework.org/schema/beans"  
3.  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
4.  xmlns:context="http://www.springframework.org/schema/context"  
5.  xsi:schemaLocation="http://www.springframework.org/schema/beans   
6.  http://www.springframework.org/schema/beans/spring-beans-2.5.xsd  
7.  http://www.springframework.org/schema/context  
8.  http://www.springframework.org/schema/context/spring-context-2.5.xsd">  
9.    
10.  <context:annotation-config/>  
11.    
12.  <!-- <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/> -->  
13.    
14.  <bean name="accountDao" class="org.myjavaswtech.dao.AccountDAO">  
15.  </bean>  
16.   
17.  <bean name="accountService" class="org.myjavaswtech.service.AccountService" dependency-check="objects">  
18.   <!-- <property name="accountDao" ref="accountDao" /> -->  
19.  </bean>  
20.   
21.  <bean name="accountBean" class="org.myjavaswtech.beans.AccountBean" >  
22.   <property name="senderAcNo" value="ac123456"/>  
23.   <property name="beneficiaryAcNo" value="ac7890" />  
24.   <property name="amount" value="10000"/>  
25.   <property name="accountService" ref="accountService"/>  
26.  </bean>  
27.   
28. </beans>  

In the above configuration we used context namespace and schema location.

Namespace:  xmlns:context="http://www.springframework.org/schema/context

SchemaLocation: http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context-2.5.xsd

Now Run the application: You'll get the following exception

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'accountService' defined in class path resource [beans.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'accountDao' is required for bean 'accountService'.