simple working example of AOP Introduction

[biocode]

Hello, world!

I'm trying to understand how to use AOP Introductions. A simple yet complete and working example would help me tremendously.

Here is my toy application (getter & setters not shown for brevity):

Car.java

public Class Car {

    private boolean fourDoor;
    //getter & setter

}

I would like to introduce an attribute to hold a string for the paint color in my Car objects. My understanding so far is that I need to create an interface for the attribute I want to add:

PaintColor.java

public interface PaintColor {

    public String getColor();
    public void setColor(String color);

}

Then I need to implement the interface by extending the DelegatingIntroductionInterceptor:

PaintColorMixin.java

import org.springframework.aop.support.DelegatingIntroductionInterceptor;

public class PaintColorMixin extends DelegatingIntroductionInterceptor {

    private String color;
    //getter & setter

}

Here is my spring config file:

CarApp.xml

...snip xml stuff...
<beans>
    <bean id="carTarget"  class"Car" singleton="false"></bean>

    <bean id="paintColorMixin" class="PaintColorMixin" singleton="false"></bean>

    <bean id="paintColorAdvisor" class="org.springframework.aop.support.DefaultIntroductionAdvisor" singleton="false">
        <constructor-arg>
            <ref bean="paintColorMixin">
        </constructor-arg>
    </bean>

    <bean id="car"  class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="proxyTargetClass"> <value>true</value> </property>
        <property name="singleton"> <value>false</value> </property>
        <property name="proxyInterfaces"> <value>PaintColor</value> </property>
        <property name="paintColorAdvisor"> <value>paintColorAdvisor</value> </property>
        <property name="target"> <value ref="carTarget" </property>
    </bean>
<beans>

The paintColorAdvisor property of the car bean seems suspicious. The value suggested in Spring In Action pp. 119 recommends "<list><value>servletAction</value></list>".

I'm not confident in my configuration, and I'm at a loss for how I'm supposed to use the enhanced car object in client code.

Any nudge (or mule kick) in the right direction is greatly appreciated.

Best regards,
Tony

[katentim]

At a glance I can see...

public class PaintColorMixin extends DelegatingIntroductionInterceptor {

should implement PainColor

public class PaintColorMixin extends DelegatingIntroductionInterceptor implements PaintColor  {

[katentim]

A simple yet complete and working example would help me tremendously

Try this:

package introductions;

public class Car {}

package introductions;

public interface PaintColor {
    public String getColor();
    public void setColor(String color);
}

package introductions;

import org.springframework.aop.support.DelegatingIntroductionInterceptor;

public class PaintColorMixin extends DelegatingIntroductionInterceptor
    implements PaintColor {
    private String color = "Not Set";
    public String getColor() {return color;}
    public void setColor(String color) {this.color = color;}
}

<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http&#58;//www.springframework.org/dtd/spring-beans.dtd">
<beans>

    <bean id="carTarget" class="introductions.Car" singleton="false"></bean>

    <bean id="paintColorMixin" class="introductions.PaintColorMixin" singleton="false"></bean>

    <bean id="paintColorAdvisor" class="org.springframework.aop.support.DefaultIntroductionAdvisor" singleton="false">
        <constructor-arg>
            <ref bean="paintColorMixin"/>
        </constructor-arg>
    </bean>

    <bean id="car" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="proxyTargetClass"> <value>true</value> </property>
        <property name="interceptorNames">
            <list>
                <value>paintColorAdvisor</value>
            </list>
        </property>
        <property name="target"> <ref bean="carTarget"/> </property>
    </bean>
</beans>

package introductions;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class IntroductionDriver {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext(
                "/introductions/introductions.xml");

        Car car = (Car) ctx.getBean("car");
        PaintColor carColor = (PaintColor) car;

        // test interfaces
        System.out.println("Is Car?: " + (car instanceof Car));
        System.out.println("Is PaintColor?: " + (car instanceof PaintColor));

        // test is modified implementation
        System.out.println("Get color: " + carColor.getColor());
        carColor.setColor("Blue");
        System.out.println("Get color: " + carColor.getColor());
        carColor.setColor("Red");
        System.out.println("Get color: " + carColor.getColor());
    }
}

[biocode]

Thank you, katentim. That's just what I needed. It's working great