Spring @Required annotation not working as expected.

Question

I'm trying to test out Spring Annotations to see how they work with some simple examples derived from the Spring 3.0 Source (in this case the "@Required" annotation specifically).

To start, I came up with a basic "Hello World" type example that doesn't use any annotations. This works as expected (i.e. prints "Hello Spring 3.0~!").

I then added a DAO object field to the Spring3HelloWorld class. My intention was to deliberately cause an exception to occur by annotating the setter for the DAO with @Required but then not setting it. However, I get a null pointer exception (since this.dao is null) when I was expecting an exception based on not following the annotation "rules/requirements".

I thought I would have needed to set the DAO object before calling any method from Spring3HelloWorld, but apparently that's not the case. I assume I'm misunderstanding how @Required works.

So basically how would I get the following to give me an error along the lines of "Hey you can't do that, you forgot to set DAO blah blah blah".

Spring3HelloWorldTest.java:

import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;

public class Spring3HelloWorldTest {

    public static void main(String[] args) {

        XmlBeanFactory beanFactory = new XmlBeanFactory(new ClassPathResource     ("SpringHelloWorld.xml"));

        Spring3HelloWorld myBean = (Spring3HelloWorld) beanFactory.getBean("spring3HelloWorldBean");
        myBean.sayHello();        

    }
}

Spring3HelloWorld.java:

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

public class Spring3HelloWorld {

    private DAO dao;

    @Required
    public void setDAO( DAO dao ){
        this.dao = dao;
    }

    public void sayHello(){
        System.out.println( "Hello Spring 3.0~!" );

        //public field just for testing
        this.dao.word = "BANANA!!!";
    }
}

SpringHelloWorld.xml:

<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"&gt;

    <context:annotation-config/>

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

    <bean id="dao" class="src.DAO" ></bean>
    <bean id="spring3HelloWorldBean" class="src.Spring3HelloWorld" ></bean>

</beans>

Answer 1

My first guess is you won't get any of the advanced behaviour with Spring and annotations because you are using an XmlBeanFactory instead of the recommended ApplicationContext.

-- edit --

Yup - see this Stack Overflow question/answer.