我试图实现我们的stackoverflow成员在这里Logging entry, exit and exceptions for methods in java using aspects给出的建议之一.由于这本身就是不同的问题,再次在这里发布.

我试图搜索,但看起来不同的版本有不同的方式,并无法在网上找出一个例子.我尝试了以下简单示例,因为我是面向方面编程的新手,无法弄清楚如何实现.这个例子是投掷NPE.请帮我理解我做错了什么.

====例外

Exception in thread "main" java.lang.NullPointerException

at aoplogging.SimpleCall.call(SimpleCall.java:13)

at aoplogging.App.main(App.java:18)

正好在SimpleService.simpleCall();

ApplicationContext的：

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"

xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context"

xmlns:jee="http://www.springframework.org/schema/jee" xmlns:tx="http://www.springframework.org/schema/tx"

xmlns:task="http://www.springframework.org/schema/task"

xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.2.xsd">

==================

App.java

package aoplogging;

import org.springframework.context.ConfigurableApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {

public static void main(String[] args) {

ConfigurableApplicationContext context = new ClassPathXmlApplicationContext("ApplicationContext.xml");

SimpleCall call =(SimpleCall) context.getBean("simpleCall");

call.call();

context.close();

}

============ SimpleCall.java

????包aoplogging;

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

public class SimpleCall {

@Autowired

private SimpleService SimpleService;

public void call(){

SimpleService.simpleCall();

try {

SimpleService.processingOperator();

} catch (SMSProcessingException | SMSSystemException e) {

e.printStackTrace();

}

}

}

===== Logging.java

package aoplogging;

import org.aspectj.lang.annotation.After;

import org.aspectj.lang.annotation.AfterReturning;

import org.aspectj.lang.annotation.AfterThrowing;

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Before;

import org.aspectj.lang.annotation.Pointcut;

@Aspect

public class Logging {

@Pointcut("execution(* aoplogging.*.*(..))")

private void selectAll(){}

/**

* This is the method which I would like to execute

* before a selected method execution.

*/

@Before("selectAll()")

public void beforeAdvice(){

System.out.println("Going to setup student profile.");

}

/**

* This is the method which I would like to execute

* after a selected method execution.

*/

@After("selectAll()")

public void afterAdvice(){

System.out.println("Student profile has been setup.");

}

/**

* This is the method which I would like to execute

* when any method returns.

*/

@AfterReturning(pointcut = "selectAll()", returning="retVal")

public void afterReturningAdvice(Object retVal){

System.out.println("Returning:" + retVal.toString() );

}

/**

* This is the method which I would like to execute

* if there is an exception raised by any method.

*/

@AfterThrowing(pointcut = "selectAll()", throwing = "ex")

public void AfterThrowingAdvice(IllegalArgumentException ex){

System.out.println("There has been an exception: " + ex.toString());

}

}