20Spring切面的优先级

通过使用@order注解指定切面的优先级，值越小，优先级越高代码：

package com.cn.spring.aop.impl;
//加减乘除的接口类
public interface ArithmeticCalculator {
    int add(int i, int j);
    int sub(int i, int j);
    int mul(int i, int j);
    int div(int i, int j);
}

package com.cn.spring.aop.impl;

import org.springframework.stereotype.Component;

//实现类
@Component
public class ArithmeticCalculatorImpl implements ArithmeticCalculator {
    @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;
    }
}

package com.cn.spring.aop.impl;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.util.Arrays;
import java.util.List;

//把这个类声明为一个切面：首先需要把该类放入到IOC容器中，在声明为一个切面
//可以使用@order注解指定切面的优先级，值越小，优先级越高
@Order(2)
@Aspect
@Component
public class LoggingAspect {

    //声明该方法是一个前置通知：在目标方法开始之前执行
    @Before("execution(public int ArithmeticCalculator.*(int, int))")
    public void beforeMethod(JoinPoint joinPoint) {
        String methodName = joinPoint.getSignature().getName();
        List<Object> args = Arrays.asList(joinPoint.getArgs());

        System.out.println("The method " +  methodName + " begins with " + args);
    }

    //后置通知：在目标方法执行后（无论是否发生异常），执行的通知
    //在后置通知中还不能访问目标方法执行的结果
    @After("execution(public int ArithmeticCalculator.*(int, int))")
    public void afterMethod(JoinPoint joinPoint) {
        String methodName = joinPoint.getSignature().getName();
        List<Object> args = Arrays.asList(joinPoint.getArgs());

        System.out.println("The method " +  methodName + " ends with " + args);
    }

    /**
     * 在方法正常结束后执行的代码
     * 返回通知是可以访问到方法的返回值
     * @param joinPoint
     */
    @AfterReturning(value = "execution(public int ArithmeticCalculator.*(int, int))",
    returning = "result")
    public void afterReturning(JoinPoint joinPoint, Object result) {
        String methodName = joinPoint.getSignature().getName();
        List<Object> args = Arrays.asList(joinPoint.getArgs());

        System.out.println("The method  ends witd " + result);
    }

    //在目标方法出现异常时会执行的代码
    //可以访问到异常对象；且可以指定在出现特定异常时再执行通知代码
    @AfterThrowing(value = "execution(public int ArithmeticCalculator.*(int, int))",
            throwing = "ex")
    public void afterReturning(JoinPoint joinPoint, Exception ex) {
        String methodName = joinPoint.getSignature().getName();

        System.out.println("The method " +  methodName + " occures exception with: " + ex);
    }

    /**
     * 环绕通知需要携带ProceedingJoinPoint类型的参数
     * 环绕通知类似于动态代理的全过程：ProceedingJoinPoint类型的参数可以决定是否执行目标方法
     * 且环绕通知必须有返回值，返回值为目标方法的返回值
     * @param proceedingJoinPoint
     */
    @Around("execution(public int ArithmeticCalculator.*(int, int))")
    public Object aroundMethod(ProceedingJoinPoint proceedingJoinPoint) {
        Object result = null;
        String methodName = proceedingJoinPoint.getSignature().getName();
        //执行目标方法
        try {
            //前置通知
            System.out.println("The method " +  methodName + " begins with " + Arrays.asList(proceedingJoinPoint.getArgs()));
            result = proceedingJoinPoint.proceed();
            //返回通知
            System.out.println("The method ends with " + result);
        } catch (Throwable throwable) {
            //异常通知
            System.out.println("The method " +  methodName + " occures exception with: " + throwable);
            throw new RuntimeException(throwable);
        }
        //后置通知
        System.out.println("The method " +  methodName + " ends");
        return result;
    }
}

package com.cn.spring.aop.impl;

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

import java.util.Arrays;

/**
 * Created by jecyhw on 2015/6/21.
 */
@Order(1)
@Aspect
@Component
public class ValidationAspect {

    @Before("execution(public int ArithmeticCalculator.*(..))")
    public void validateArgs(JoinPoint joinPoint) {
        System.out.println("validate:" + Arrays.asList(joinPoint.getArgs()));
    }
}

package com.cn.spring.aop.impl;

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

public class Main {
    public static void main(String[] args) {
        //1.创建Spring的IOC容器
        ApplicationContext ctx = new ClassPathXmlApplicationContext("17-1.xml");

        //2.从IOC容器中huo获取bean的实例
        ArithmeticCalculator arithmeticCalculator = ctx.getBean(ArithmeticCalculator.class);

        //3.使用bean
        int result = arithmeticCalculator.add(3, 6);

        System.out.println("result:" + result);
        //result = arithmeticCalculator.div(3, 0);
       // System.out.println("result:" + result);
    }
}

<?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/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
    <context:component-scan base-package="com.cn.spring.aop.impl">
    </context:component-scan>

    <!--使AspjectJ注解起作用：自动为匹配的类生成代理对象-->
    <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
</beans>