Review

昨天我們學到了AOP的使用場景，可以把loggin、稽核、效能監控的這些關注面向Cross-cutting concerns抽離出來模組化，讓我們只關注在商業邏輯上

今日我們先用前一天的例子來解釋AOP中的專業術語，再用一個快速入門範例來熟悉Spring AOP的操作

導入JAR

spring-aspects-5.3.22.jar是在spring framework 5.2.22.RELEASE中可以找到，另外3個spring加強版的AOP jar需去maven自行下載引入

AOP專業術語說明

• Aspect：A modularization of a concern that cuts across multiple classes.

  代表一個Cross-Cutting Concerns例如logging、稽核、效能監控等，以上圖來說我們關注的就是logging這個切面

• Advice：Action taken by an aspect at a particular join point

  指的是我們在切入點執行的動作，以上圖來說就是通知方法

• Pointcut：A predicate that matches join points

  一個預期可以切入的點，以上圖來說我們在logging中關心方法開始、結束、返回、異常這些地方，以上圖來說就是連接點

• Join point：pointcut expression：A pointcut declaration has two parts: a signature comprising a name and any parameters and a pointcut expression that determines exactly which method executions we are interested in.

  希望那些地方切入執行通知方法，例如上圖(紅色圓圈)，我們希望div method方法異常的時侯留個log或是mul method執行的結果是我們在意的點。程式透過pointcut expression的設定來找出join point

Advice Type

• Before advice：runs before a join point
• After returning advice：run after a join point completes normally
• After throwing advice:Advice to be run if a method exits by throwing an exception.
• After (finally) advice：a join point exits (normal or exceptional return)
• Around advice: Advice that surrounds a join point such as a method invocation.

Advice Annotation

• @Before：前置通知
• @After：後置通知
• @AfterReturning：返回通知
• @AfterThrowing：異常通知
• @Around：環繞通知

快速入門範例

延續前一日範例，改寫為AOP版本

public interface Calculator {
    int add(int i,int j);
    int sub(int i,int j);
    int mul(int i,int j);
    int div(int i,int j);
}

@Service
public class MyCalculator implements Calculator{
    @Override
    public int add(int i, int j) {
        int result = i+j;
        return result;
    }

    @Override
    public int sub(int i, int j) {
        int result = i-j;
        return result;
    }

    @Override
    public int mul(int i, int j) {
        int result = i*j;
        return result;
    }

    @Override
    public int div(int i, int j) {
        int result = i/j;
        return result;
    }
}

@Aspect
@Component
public class LogUtils {
    //想在目標方法之前執行
    @Before("execution(public int com.swj.MyCalculator.*(int,int))")
    public static void logStart(){
        System.out.println("method start");
    }
    //想在目標方法正常執行完成後執行
    @AfterReturning("execution(public int com.swj.MyCalculator.*(int,int))")
    public static void logReturn(){
        System.out.println("method completed,result is");
    }
    @After("execution(public int com.swj.MyCalculator.*(int,int))")
    public static void logEnd(){
        System.out.println("method end");
    }
    //想在目標方法結束後執行
    @AfterThrowing("execution(public int com.swj.MyCalculator.*(int,int))")
    public static void logException(){
        System.out.println("method throws exception");
    }

}

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

    <context:component-scan base-package="com.swj"></context:component-scan>
    <!-- 啟動AOP   -->
    <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
</beans>

@Test
public void testDay18(){
    ApplicationContext ioc = new ClassPathXmlApplicationContext("bean18.xml");
    System.out.println("容器啟動完成....");
    Calculator calculator = ioc.getBean(Calculator.class);
    calculator.add(1,1);
    System.out.println("=========");
    calculator.div(1,0);
}

Result

Reference

• Spring AOP简单了解（雷丰阳老师的笔记） - 国服第一邓特蒙