Aspect not working witha spring bean

I am trying to create a simple aspect . Here is my simple spring bean

public class SimpleService {
    public void sayHello(){
        System.out.println("hi");
    }

}

Here is my aspect class

@Aspect
public class SimpleAspect {
    @Before("execution(void sayHello())")
    public void entering(){
        System.out.println("entering..");
    }
}

Here is my configuration file

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://ift.tt/GArMu6"
    xmlns:xsi="http://ift.tt/ra1lAU"
    xmlns:aop="http://ift.tt/OpNdV1"
    xsi:schemaLocation="http://ift.tt/OpNdV1 http://ift.tt/1oTOpwm
        http://ift.tt/GArMu6 http://ift.tt/1jdM0fG">
         <aop:aspectj-autoproxy/>
<bean id="service" class="com.schatt.service.SimpleService"></bean>

My understanding was that when I try to invoke SimpleService.sayHello() , the before aspect will be called and after that sayHello() will be called.But the aspect is not getting triggered.Can not understand what I am missing here.