@Around annotation / <aop:around> Configaration in XML file, showing unexpected Output

[Ramakrishna Udupa]

Hi All,

I posted all my code below.

spring.xml

<?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:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/aop 
  http://www.springframework.org/schema/aop/spring-aop-3.2.xsd">

	<aop:aspectj-autoproxy />

	<bean id="shape" class="org..rk.Shape" autowire="byName" />

	<bean id="circle" class="org..rk.Circle">
		<property name="name" value="Simple Circle" />
	</bean>

	<bean id="triangle" class="org..rk.Triangle">
		<property name="name" value="Equilateral Triangle" />
	</bean>

	<bean id="loggingAspect" class="org..rk.LoggingAspect" />
	
	<!-- <aop:config>
		<aop:aspect id="loggingAspect" ref="loggingAspect">
		<aop:pointcut expression="execution(* get*())" id="allGetter"/>
			<aop:around pointcut-ref="allGetter" method="AroundAdvice"/>
		</aop:aspect>
	
	</aop:config> -->

</beans>

LoggingAspect.java

package org.rk;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class LoggingAspect {
	
	@Around("execution(* *())")
	public void AroundAdvice(ProceedingJoinPoint proceedingJoinPoint) {
		try {
			System.out.println("Before Advice");
			proceedingJoinPoint.proceed();
			System.out.println("After Advice");
		} catch (Throwable e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

Triangle.java

package org.rk;

public class Triangle extends Shape {

	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

}

Circle.java

package org.rk;

public class Circle extends Shape {
	
	private String name;

	public String getName() {
		System.out.println("Between Advice.. In getName");
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

}

Sahpe.java

package org.rk;

public class Shape {
private Triangle triangle;
private Circle circle;
public Triangle getTriangle() {
	return triangle;
}
public void setTriangle(Triangle triangle) {
	this.triangle = triangle;
}
public Circle getCircle() {
	System.out.println("Between Advice.. In getCircle");
	return circle;
}
public void setCircle(Circle circle) {
	this.circle = circle;
}
}

AopTester.java

package org.rk;

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

public class AOPTester {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
		Shape shape = applicationContext.getBean("shape", Shape.class);
LINE 1		shape.getCircle();
	}

}

Output is:

Before Advice
Between Advice.. In getCircle
After Advice

Its perfect. But, In AOPTester.java if you replace LINE 1 as

shape.getCircle().getName();

It's giving NullPointerException. I thought output would be

Before Advice
Between Advice.. In getCircle
After Advice
Before Advice
Between Advice.. In getName
After Advice

Can anyone Explain me, what's happening(cause for exception) when I call

shape.getCircle().getName();

?


Second Doubt:
When I print that, like

System.out.println(shape.getCircle().getName());

It's showing "null". why?
Thanks:
Ramakrishna k.c

[Jayesh A Lalwani]

You have not initialized the circle member inside your shape. So, shape.getCircle returns null. When you try to call getName on shape.getCircle, you get a NPE.

You should inject the circle into the shape.

[Ramakrishna Udupa]

Jayesh A Lalwani wrote:You have not initialized the circle member inside your shape. So, shape.getCircle returns null. When you try to call getName on shape.getCircle, you get a NPE.

You should inject the circle into the shape.

Why should I initialize that? In spring.xml, I think the below line will take care of initialization.

<bean id="shape" class="org.rk.Shape" autowire="byName" />

am I right?

[H Paul]

1. With debugger + doc:
There is NO issue with DI autowired byName.
The issue is with the @Around advice code.

2. Read
From Sprimg 4.0.4.RELEASE doc:
8. Aspect Oriented Programming with Spring
Around advice page 204
public class AroundExample

3. See green Comment. You need to return the Object. (Your version did not.)

@Aspect  
public class LoggingAspect {  

    @Around("execution(* *.*(..))")  
    public Object aroundAdvice(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {  
        try {  
            System.out.println("Before Advice");  
            Object result = proceedingJoinPoint.proceed();   // >>>>> See public Circle getCircle() return Circle  
            System.out.println("After Advice");  
            return result;
        } catch (Throwable e) {  
            e.printStackTrace();
            throw e;
        }  
    }