Table of Contents
The @Required annotation in Spring applies to bean property setter methods, as in the following example:
Tutorial Content: Spring tutorial for beginners
- Introduction to spring framework
- Spring interview questions
- Dependency injection(ioc) in spring
- Spring hello world example in eclipse
- Spring java based configuaration
- Dependency injection via setter method in spring
- Dependency injection via constructor in spring
- Spring Bean scopes with examples
- Initializing collections in spring
- Beans Autowiring in spring
- Inheritance in Spring
- Spring ApplicationContext
- Spring lifetime callbacks
- BeanPostProcessors in Spring
- Annotation based Configuration in spring
- Spring AOP tutorial
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package org.arpit.javapostsforlearning; public class Country { Capital capital; @Required public void setCapital(Capital capital) { this.capital = capital; } } |
NullPointerExceptions or the like later on.
Suppose you have very large application and you get NullPointerExceptions because required dependency has not been injected then it is very hard to find out what goes wrong.So this annotation helps us in debugging the code.
Example:
For configuring spring in your eclipse ide please refer hello world example
1.Country.java:
This is simple pojo class having some attributes so here country has name and object of Capital class.
Create Country.java under package org.arpit.javapostsforlearning.Copy following content into Country.java.
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package org.arpit.javapostsforlearning; import org.springframework.beans.factory.annotation.Required; public class Country { String countryName; Capital capital; public String getCountryName() { return countryName; } public void setCountryName(String countryName) { this.countryName = countryName; } public Capital getCapital() { return capital; } @Required public void setCapital(Capital capital) { this.capital = capital; } } |
2.Capital.java
This is also simple pojo class having one attribute called “capitalName”.
Create Capital.java under package org.arpit.javapostsforlearning.java.Above Country class contains object of this class.Copy following content into Capital.java
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package org.arpit.javapostsforlearning; public class Capital { String capitalName; public String getCapitalName() { return capitalName; } public void setCapitalName(String capitalName) { this.capitalName = capitalName; } } |
3.ApplicationContext.xml
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<?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/> <bean id="CountryBean" class="org.arpit.javapostsforlearning.Country"> <property name="countryName" value="India" /> </bean> <bean id="CaptialBean" class="org.arpit.javapostsforlearning.Capital"> <property name="capitalName" value="Delhi" /> </bean> </beans> |
Now you can note here that we have not injected capital property into country class but we have used it for getting capitalName in below RequiredAnnotationInSpringMain class.
4.RequiredAnnotationInSpringMain.java
This class contains main function.Create RequiredAnnotationInSpringMain.java under package org.arpit.javapostsforlearning.Copy following content into RequiredAnnotationInSpringMain.java
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package org.arpit.javapostsforlearning; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class RequiredAnnotationInSpringMain{ public static void main(String[] args) { ApplicationContext appContext = new ClassPathXmlApplicationContext("ApplicationContext.xml"); Country countryObj = (Country) appContext.getBean("CountryBean"); String countryName=countryObj.getCountryName(); Capital capital=countryObj.getCapital(); String capitalName=capital.getCapitalName(); System.out.println(capitalName+" is capital of "+countryName); } } |
5.Run it:
When you will run above application,you will get following as output.
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Sep 01, 2012 1:43:16 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@17a1767: startup date [Sat Sep 01 13:43:16 IST 2012]; root of context hierarchy Sep 01, 2012 1:43:17 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions INFO: Loading XML bean definitions from class path resource [ApplicationContext.xml] Sep 01, 2012 1:43:17 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@54446d: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,CountryBean,CaptialBean,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy Sep 01, 2012 1:43:17 PM org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons INFO: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@54446d: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,CountryBean,CaptialBean,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'CountryBean' defined in class path resource [ApplicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'capital' is required for bean 'CountryBean' 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:585) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464) at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.(ClassPathXmlApplicationContext.java:83) at org.arpit.javapostsforlearning.SetterInjectionMain.main(SetterInjectionMain.java:11) Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'capital' is required for bean 'CountryBean' 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 |
That’s all about Required annotation in Spring.
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