IOC和AOP是Spring的两大基石。
AOP前奏
代码实现片段
问题
- 代码混乱:越来越多的非业务需求(日志和验证等)加入后,原有的业务方法急剧膨胀。每个方法在处理核心逻辑的同时还必须兼顾其他多个关注点
- 代码分散:以日志需求为例,只是为了满足这个单一需求,就不得不在多个模块(方法)里多次重复相同的日志代码。如果日志需求发生变化,必须修改所有模块
使用动态代理解决上述问题(开发不建议使用,对程序员要求较高,推荐AOP解决这个问题)
- 代理设计模式的原理:使用一个代理将对象包装起来,然后用该代理对象取代原始对象。任何对原始对象的调用都要通过代理。代理对象决定是否以及何时将方法调用转到原始对象上。
例子程序
基本结构
ArithmeticCalculator.java
package com.spring.aop.helloworld;
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);
}
ArithmeticCaluculatorImpl.java
package com.spring.aop.helloworld;
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;
}
}
ArithmeticCalculatorLoggingImpl.java
package com.spring.aop.helloworld;
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;
}
}
ArithmeticCalculatorLoggingProxy.java
package com.spring.aop.helloworld;
import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
public class ArithmeticCalculatorLoggingProxy {
//要代理的对象
private ArithmeticCalculator target;
public ArithmeticCalculatorLoggingProxy(ArithmeticCalculator target){
this.target = target;
}
public ArithmeticCalculator getLoggingProxy(){
ArithmeticCalculator proxy = null;
//代理对象由哪一个类加载器负责加载
ClassLoader loader = target.getClass().getClassLoader();
//代理对象的类型,即其中有哪些方法
Class [] interfaces = new Class[]{ArithmeticCalculator.class};
//当调用代理对象其中的方法时,该执行的代码
InvocationHandler h = new InvocationHandler() {
/**
* proxy:正在返回的那个代理对象,一般情况下,在invoke方法中都不使用该对象。
* method:正在被调用的方法
* args:调用方法时,传入的参数
* @param proxy
* @param method
* @param args
* @return
* @throws Throwable
*/
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//这里如果这样写会造成死循环System.out.println(proxy.toString());
String methodName = method.getName();
//日志
System.out.println("ATGUIGU->The method "+methodName+" begins with "+ Arrays.asList(args));
//执行方法
Object result = method.invoke(target,args);
//日志
System.out.println("ATGUIGU->The method "+methodName+" ends with "+result);
return result ;
}
};
proxy = (ArithmeticCalculator) Proxy.newProxyInstance(loader,interfaces,h);
return proxy;
}
}
Main.java
package com.spring.aop.helloworld;
public class Main {
public static void main(String[] args){
// ArithmeticCalculator arithmeticCalculator = null;
// arithmeticCalculator = new ArithmeticCalculatorLoggingImpl();
ArithmeticCalculator target = new ArithmeticCalculatorImpl();
ArithmeticCalculator proxy = new ArithmeticCalculatorLoggingProxy(target).getLoggingProxy();
int result = proxy.add(1,2);
System.out.println("-->"+result);
result = proxy .div(4,2);
System.out.println("-->"+result);
}
}