aspectJ 示例中的空指针异常

Question

我正在尝试实施我们的 Whosebug 成员在此给出的建议之一。由于这本身是不同的问题，因此再次发帖。

我试过搜索，但看起来不同版本的搜索方式不同，无法在网上找到示例。我尝试了以下简单示例，因为我是面向方面编程的新手并且无法弄清楚如何实现。这个例子正在抛出 NPE。请帮助我了解我哪里做错了。

====异常

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();

应用程序上下文：

<beans xmlns="http://www.springframework.org/schema/beans"
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">


<aop:aspectj-autoproxy />
<bean id="simpleCall" class="aoplogging.SimpleCall" />

================== 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());   
   }

}

Answer 1

我支持我的建议;)。

Spring AOP/AspectJ 的用法在使用未通过使用接口注入的 bean 时存在问题（使用接口吃掉了注入点），因为接口由 AspectJ 代理。

有一种方法可以通过将 proxy-target-class="true" 添加到

来解决这个问题

<aop:aspectj-autoproxy />

但这不是一个好方法。

使用接口更简单、更安全。

编辑：另一个错误是您缺少实现 SimpleService 的 bean。添加

会更容易

<context:component-scan base-package="aoplogging" />

给你的 applicationContext.xml.

然后，你必须用

标记所有bean

@Component

为了让Spring知道它们是Spring应该实例化的bean。

编辑：必须用 @Aspect 和 @Component 注释方面才能让 Spring 检测到它。

aspectJ 示例中的空指针异常

nullpointer exception in aspectJ example

java

spring

aspectj

spring-aop

pointcut