责任链模式

责任链模式

介绍

责任链模式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。

 

避免请求发送者与接收者耦合在一起，让多个对象都有可能接收请求，将这些对象连接成一条链，并且沿着这条链传递请求，直到有对象处理它为止。

 

使用

StateRoadRoadIncidentHandler（省） 《《 MunicipalityRoadRoadIncidentHandler（市） 《《 TownRoadRoadIncidentHandler（镇）

public interface RoadIncidentHandler {

    void handle(RoadIncident roadIncident);

    boolean withinBounds(double lat, double lng);

}

　　

/**
 *  省
 *
 */
@Slf4j
public class StateRoadRoadIncidentHandler implements RoadIncidentHandler {

    @Override
    public void handle(RoadIncident roadIncident) {
        //经纬度不在该省范围内
        if(!withinBounds(roadIncident.getLatitude(),roadIncident.getLatitude())) {
            throw new IllegalArgumentException("Incident cannot be handled by state. No successor available");
        }

        /**
         * Handle the incident
         */
        log.info("sheng...");
    }

    @Override
    public boolean withinBounds(double lat, double lng) {

        /**
         * Reverse geolocation, look up by name, radius based distance etc.
         */

        return true;
    }
}

　　

/**
 *  市
 *
 */
@Slf4j
public class MunicipalityRoadRoadIncidentHandler implements RoadIncidentHandler {

    private final RoadIncidentHandler successor;

    public MunicipalityRoadRoadIncidentHandler(final RoadIncidentHandler successor) {
        this.successor = successor;
    }

    @Override
    public void handle(RoadIncident roadIncident) {
        //经纬度不在该市范围内
        if(!withinBounds(roadIncident.getLatitude(),roadIncident.getLongtitude())) {
            successor.handle(roadIncident);
        } else {
            /**
             * Handle the incident
             */
            log.info("shi...");
        }
    }

    @Override
    public boolean withinBounds(double lat, double lng) {
        /**
         * Reverse geolocation, look up by name, radius based distance etc.
         */
        return false;
    }
}

　　

/**
 *  镇
 *
 */
@Slf4j
public class TownRoadRoadIncidentHandler implements RoadIncidentHandler {

    private final RoadIncidentHandler successor;

    public TownRoadRoadIncidentHandler(final RoadIncidentHandler successor) {
        this.successor = successor;
    }

    @Override
    public void handle(RoadIncident roadIncident) {
        //经纬度不在该镇范围内
        if(!withinBounds(roadIncident.getLatitude(),roadIncident.getLongtitude())) {
            successor.handle(roadIncident);
        } else {
            /**
             * Handle the incident
             */
            log.info("zhen...");
        }
    }

    @Override
    public boolean withinBounds(double lat, double lng) {
        /**
         * Reverse geolocation, look up by name, radius based distance etc.
         */
        return false;
    }
}

　　将请求发送到职责链上

• 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。
• 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。
• 可动态指定一组对象处理请求。

StateRoadRoadIncidentHandler state = new StateRoadRoadIncidentHandler();
MunicipalityRoadRoadIncidentHandler municipality = new MunicipalityRoadRoadIncidentHandler(state);
TownRoadRoadIncidentHandler firstTown = new TownRoadRoadIncidentHandler(municipality);
        

RoadIncident roadIncident = new RoadIncident(0d,0d,"Something happened");
firstTown.handle(roadIncident);