设计模式之责任链模式

责任链模式应用

1. 责任链模式介绍

责任链模式（Chain of Responsibility Pattern）为请求创建了一个接收者对象的链。这种模式给予请求的类型，对请求的发送者和接收者进行解耦。这种类型的设计模式属于行为型模式。在这种模式中，通常每个接收者都包含对另一个接收者的引用。如果一个对象不能处理该请求，那么它会把相同的请求传给下一个接收者，依此类推。

2. 应用场景

• 1). 有多个对象可以处理同一个请求，具体哪个对象处理该请求由运行时刻自动确定。
• 2). 在不明确指定接收者的情况下，向多个对象中的一个提交一个请求。
• 3). 可动态指定一组对象处理请求。

3. 实现(以创建订单为例子)

步骤一

创建一个接口:

package com.example.demo.designmodel.chain3;

import org.springframework.core.Ordered;

/**
 * @author: robin
 * @date: 2020/8/6 4:44 PM
 * @aphorism: "stay hungry, stay foolish"
 */
public interface AbstractOrderHandler extends Ordered {
    /**
     *
     * provide abstract method
     *
     * @param stage
     * @param ride
     * @return
     */
    Boolean doHandler(int stage, GreenChannelOrder ride);
}

步骤二

创建责任链处理器添加后继处理器:

package com.example.demo.designmodel.chain3;

import com.google.common.collect.Maps;
import org.springframework.stereotype.Component;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;

/**
 * Chain of Responsibility Pattern
 * Ensure link order
 */

@Component
public class OrderHandlerChain {

    private List<AbstractOrderHandler> baseHandlers;


    //private Map<String, AbstractOrderHandler> map2 = Maps.newHashMapWithExpectedSize(3);

    public OrderHandlerChain(List<AbstractOrderHandler> baseHandlers) {
        baseHandlers.sort(Comparator.comparing(AbstractOrderHandler::getOrder));
       /*  Map<String, AbstractOrderHandler> map = Maps.newHashMapWithExpectedSize(3);

       for(AbstractOrderHandler handler:baseHandlers){
            map.put(handler.handLerName(),handler);
        }
*/
        // this.map2=baseHandlers.stream().collect(Collectors.toMap(AbstractOrderHandler::handLerName, a -> a,(k1, k2)->k1));

        this.baseHandlers = Collections.unmodifiableList(baseHandlers);
    }

   /* public AbstractOrderHandler getAbstractHandler(String handlerName){
        return map2.get(handlerName);
    }*/


    public void handle(int stage, GreenChannelOrder ride) {
        boolean handle = false;
        for (AbstractOrderHandler baseHandler : baseHandlers) {
            if (!handle) {
                handle = baseHandler.doHandler(stage, ride);
            }
        }
    }
}

步骤三
创建具体的职责处理类
1)预置订单处理器

package com.example.demo.designmodel.chain3;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

/**
 * @author: robin
 * @date: 2020/8/6 4:46 PM
 * @aphorism: "stay hungry, stay foolish"
 */
@Slf4j
@Component
public class PreOrderHandler implements AbstractOrderHandler {


    @Override
    public Boolean doHandler(int stage, GreenChannelOrder ride) {
        if (stage <= 1) { //预置订单处理职责
            log.info("阶段1");
            System.out.println("阶段1");
            return false;
        }
        return false;//继续传递
    }


    @Override
    public int getOrder() {
        return 0;
    }
}

2)开始订单处理器

package com.example.demo.designmodel.chain3;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

/**
 * @author: robin
 * @date: 2020/8/6 4:46 PM
 * @aphorism: "stay hungry, stay foolish"
 */
@Slf4j
@Component
public class StartOrderHandler implements AbstractOrderHandler {


    @Override
    public Boolean doHandler(int stage, GreenChannelOrder ride) {
        if (stage <= 2) {//开始订单处理职责
            log.info("阶段2");
            return true;
        }
        return false;
    }

    @Override
    public int getOrder() {
        return 1;
    }
}

3)结束订单处理器

package com.example.demo.designmodel.chain3;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

/**
 * @author: robin
 * @date: 2020/8/6 4:46 PM
 * @aphorism: "stay hungry, stay foolish"
 */
@Slf4j
@Component
public class FinishOrderHandler implements AbstractOrderHandler {


    @Override
    public Boolean doHandler(int stage, GreenChannelOrder ride) {
        if (stage <= 3) {//结束订单处理职责
            try {
                log.info("阶段3");
            } catch (Exception e) {
            }
        }
        return true;
    }

    @Override
    public int getOrder() {
        return 2;
    }
}