spring —— AOP（前置通知）

一、pom 中需要增加的依赖

    org.springframework
    spring-aop
    6.0.2


    org.springframework
    spring-aspects
    6.0.2

 二、前置通知

（一）基于 xml 的前置通知

 首先，需要在 xml 文件里做如下配置：

然后，编写目标类：

package com.spring.aop;

import org.springframework.stereotype.Component;

@Component
public class Calculator{

    public int add(int a, int b) {
        System.out.println(a+b);
        return a+b;
    }
    protected String sub(String a){
        System.out.println(a);
        return a;
    }
}

之后，设置切面类： 

package com.spring.aop;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class LogAspect {
    @Before(value = "execution(public int com.spring.aop.Calculator.add(..))")
    public void beforeMethod(){
        System.out.println("Before Method");
    }
}

最后，测试： 

import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestAop {
    @Test
    public void testAdd(){
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Calculator calculator = context.getBean(Calculator.class);
        calculator.add(2,3);
        calculator.sub("hello");
    }
}

（二）基于全注解的前置通知

目标类：

package com.spring.aop;

import org.springframework.stereotype.Component;

@Component
public class Calculator{

    public int add(int a, int b) {
        System.out.println(a+b);
        return a+b;
    }
    protected String sub(String a){
        System.out.println(a);
        return a;
    }
}

配置类：

package com.spring.aop;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("com.spring.aop")
public class SpringConfig {
}

切面类： 

package com.spring.aop;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
import org.springframework.stereotype.Component;
@EnableAspectJAutoProxy
@Aspect
@Component
public class LogAspect {
    @Before(value = "execution(public int com.spring.aop.Calculator.add(..))")
    public void beforeMethod(){
        System.out.println("Before Method");
    }
}

测试类：

package com.spring.aop;

import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TestAop {
    @Test
    public void testAdd(){
        ApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
        Calculator calculator = context.getBean(Calculator.class);
        calculator.add(2,3);
        calculator.sub("hello");
    }
}

 比较结果：

基于全注解的前置通知，等同于将 

配置在配置类的 @ComponentScan 注解中；将

配置在切面类的 @EnableAspectJAutoProxy 注解中。