spring aop学习9:Aop的链式调用(责任链模式)

一.责任链模式
1.基本的责任链模式
◆主体父类:abstract class Subject.java

package com.tiglle.responsibility.chain.model;
//主体
public abstract class Subject {

    private Subject successor;

    protected abstract void handle();

    public void execute(){
        handle();
        if(successor!=null){
            successor.execute();
        }
    }

    public Subject getSuccessor() {
        return successor;
    }

    public void setSuccessor(Subject successor) {
        this.successor = successor;
    }

}

◆子类和测试main方法:MainExec.java

package com.tiglle.responsibility.chain.model;

public class MainExec {

    private static class Part1 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part1的handle");
        }
    }
    private static class Part2 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part2的handle");
        }
    }
    private static class Part3 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part3的handle");
        }
    }


    public static void main(String[] args) {
        Part1 part1 = new Part1();
        Part2 part2 = new Part2();
        Part3 part3 = new Part3();

        part1.setSuccessor(part2);
        part2.setSuccessor(part3);

        part1.execute();
    }

}

执行结果:
Part1的handle
Part2的handle
Part3的handle

原理:
执行Part1继承自父类的execute()方法，首先执行Part1重写了父类抽象方法handle()，然后判断successor(此时successor为Part2)是否为null

此时successor(Part2)不为null，执行Part2的execute，首先执行Part2重写了父类抽象方法handle()，然后判断successor(此时successor为Part3)是否为null

此时successor(Part3)不为null，执行Part3的execute，首先执行Part3重写了父类抽象方法handle()，然后判断successor(Part3的successor为null)是否为null，为null，停止执行

2.优化的责任链模式
◆主体父类:abstract class Subject.java

package com.tiglle.responsibility.chain.model.optimization;

public abstract class Subject {

    protected abstract void handle();

    public void execute(SubjectChain successor){
        handle();
        successor.process();
    }
}

◆中间类:class SubjectChain.java

package com.tiglle.responsibility.chain.model.optimization;

import java.util.List;

public class SubjectChain {

    private List successors;

    public SubjectChain(List successors){
        this.successors = successors;
    }

    private int index = 0;

    public void process(){
        if(index < successors.size()){
            successors.get(index++).execute(this);
        }
    }
}

◆测试main方法:MainExec.java

package com.tiglle.responsibility.chain.model.optimization;

import java.util.ArrayList;
import java.util.List;

public class MainExec {

    private static class Part1 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part1的handle");
        }
    }

    private static class Part2 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part2的handle");
        }
    }

    private static class Part3 extends Subject{
        @Override
        protected void handle() {
            System.out.println("Part3的handle");
        }
    }

    public static void main(String[] args) {
        Part1 part1 = new Part1();
        Part2 part2 = new Part2();
        Part3 part3 = new Part3();
        List successors = new ArrayList<>();
        successors.add(part1);
        successors.add(part2);
        successors.add(part3);

        SubjectChain subjectChain = new SubjectChain(successors);
        subjectChain.process();
    }
}


执行结果:
Part1的handle
Part2的handle
Part3的handle

原理:两个方法的互相调用，并设置中断条件

二.spring aop的链式调用使用的第二种方法:
源码:

@Override
    public Object proceed() throws Throwable {
        //  We start with an index of -1 and increment early.
        //从-1开始每次加1
        if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
            return invokeJoinpoint();
        }

        Object interceptorOrInterceptionAdvice =
                this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
        if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
            // Evaluate dynamic method matcher here: static part will already have
            // been evaluated and found to match.
            InterceptorAndDynamicMethodMatcher dm =
                    (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
            //
            if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
                return dm.interceptor.invoke(this);
            }else {
                // Dynamic matching failed.
                // Skip this interceptor and invoke the next in the chain.
                return proceed();
            }
        }else {
            // It's an interceptor, so we just invoke it: The pointcut will have
            // been evaluated statically before this object was constructed.
            return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
        }
    }