AOP 面向切面编程详解

Posted 2020-10-02

引言

对类(class)增强的手段通常分为以下三类

1.继承  子类通过继承父类或者实现接口对类进行增强   

2.装饰者模式(Wrapper) 常用于对类的某个方法进行重写,以实现更强大的功能.常用于场合缓冲流,Struct2中StructRequestWarpper类   实现准则:是你还有你,一切全靠你

3.动态代理 一句话概括:获取实现了一组接口的类对象 需提供目标对象,增强建议  三大参数 :ClassLoader Class[] interfaces InvocationHandler  (调用目标对象的方法时会调用这)

区别与装饰者模式:装饰者模式通常是对一个类进行加强,而动态代理是获取一组接口的方法在对类进行增强

 

具体实现

package com.atguigu.spring.aop;

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.atguigu.spring.aop;

import org.springframework.stereotype.Component;

@Component("arithmeticCalculator")
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;
	}

}

　　要对Arithmetic 的add,sub,mul,div方法进行增强,添加日志方法,用到了代理

传统的做法

package com.atguigu.spring.aop;

public class ArithmeticCalculatorLoggingImpl implements ArithmeticCalculator {

	@Override
	public int add(int i, int j) {
		System.out.println("The method add begins with [" + i + "," + j + "]");
		int result = i + j;
		System.out.println("The method add ends with " + result);
		return result;
	}

	@Override
	public int sub(int i, int j) {
		System.out.println("The method sub begins with [" + i + "," + j + "]");
		int result = i - j;
		System.out.println("The method sub ends with " + result);
		return result;
	}

	@Override
	public int mul(int i, int j) {
		System.out.println("The method mul begins with [" + i + "," + j + "]");
		int result = i * j;
		System.out.println("The method mul ends with " + result);
		return result;
	}

	@Override
	public int div(int i, int j) {
		System.out.println("The method div begins with [" + i + "," + j + "]");
		int result = i / j;
		System.out.println("The method div ends with " + result);
		return result;
	}

}

　　由以上代码可以看出,相似重复的代码太多,要对改类进行重写成更简单的类,用到了到动态代理