In a production-scale application, there may be hundreds or thousands of beans declared in the IoC container, and the dependencies between them are often very complicated. One of the shortcomings of setter injection is that it’s very hard for you to check if all required properties have been set or not. Using “dependency-check” attribute of <bean> you can check if attributes values have been set but it can’t check if their value is set to null or non-null values.
Apart from verifying dependencies using dependency-check, you can use @Required annotation to check if values set are non-null.
How to use @Required annotation
1) Use @Required annotation over setter methods
Use the @Required annotation over setter method of bean property in class file as below:
public class EmployeeFactoryBean extends AbstractFactoryBean<Object>
{
private String designation;
public String getDesignation() {
return designation;
}
@Required
public void setDesignation(String designation) {
this.designation = designation;
}
//more code here
}
2) Register RequiredAnnotationBeanPostProcessor class
RequiredAnnotationBeanPostProcessor is a spring bean post processor that checks if all the bean properties with the @Required annotation have been set. To enable this bean post processor for property checking, you must register it in the Spring IoC container.
<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor" />
Demo
If any property with @Required have not been set, a BeanInitializationException will be thrown by this bean post processor. For example, if I will create an instance of EmployeeFactoryBean class without passing property value for designation, then I will get this error.
<bean id="manager" class="com.howtodoinjava.demo.factory.EmployeeFactoryBean"> <!-- <property name="designation" value="Manager" /> --> </bean> <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor" />
It will throw error.
Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'designation' is required for bean 'manager' at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:156) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1202) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537) ... 11 more
To correct this problem, pass the designation value by un-commenting the line in applicationContext.xml file.
In this way, you can use @Required annotation and RequiredAnnotationBeanPostProcessor class to verify that on context initialization, all the required bean properties have been set properly.
Happy Learning !!
Prabhat
@Configuration
public class BeanDefination {
@Bean
public Student student()
{
Student s= new Student();
//s.setName(“Shiva”);
return s;
}
}
public class Student {
public String name;
public String getName() {
return name;
}
@Required
public void setName(String name) {
this.name = name;
}
}
public class TestDemo {
public static void main(String[] args) {
// TODO Auto-generated method stub
AnnotationConfigApplicationContext factory=new AnnotationConfigApplicationContext();
factory.register(BeanDefination.class);
factory.refresh();
Student student=(Student)factory.getBean(Student.class);
System.out.println(student.getName());
}
}
My Doubt is i have mentioned @Reuired and if i am not injecting any values then it is not throwing an error
Charith
Lokesh Gupta
I used ” instead of
Its getting same output now.Is it ok if I’m using ” ?
Thanks
Lokesh Gupta
Please post the code inside [java] … [/java] tags.