java 设计模式从风控链理解责任链模式

public abstract class RiskHandler {
    /**
     * 支付方式
     */
    private String payType;
    private RiskHandler nextHandler;
    public RiskHandler(String payType) {
        this.payType = payType;
    }
    /**
     * 是否能支付
     * @param order 订单
     */
    protected abstract boolean canPay(Order order);
    /**
     * 处理器
     * @param order 订单
     * @return 返回true 或者 false
     */
    public final boolean handler(Order order){
        if(order.getPayType().equals(this.payType)){
            return this.canPay(order);
        }else {
            if (this.nextHandler != null){
                return this.nextHandler.handler(order);
            }else{
                throw new IllegalArgumentException("支付方式有误");
            }
        }
    }
    public void setNextHandler(RiskHandler handler){
        this.nextHandler = handler;
    }
}

public class CreditHandler extends RiskHandler {
    /**
     * 500 限额
     */
    private BigDecimal limitAmount = BigDecimal.valueOf(500);
    public CreditHandler() {
        super(PayTypeEnum.CREDIT.getPayType());
    }
    @Override
    protected boolean canPay(Order order) {
        if(order.getAmount().compareTo(limitAmount) < 0){
            limitAmount = limitAmount.subtract(order.getAmount());
            return true;
        }else {
            return false;
        }
    }
}

public class HuabeiHandler extends RiskHandler {
    /**
     * 300 限额
     */
    private BigDecimal limitAmount = BigDecimal.valueOf(300);
    public HuabeiHandler() {
        super(PayTypeEnum.HUA_BEI.getPayType());
    }
    @Override
    protected boolean canPay(Order order) {
        if(order.getAmount().compareTo(limitAmount) < 0){
            limitAmount = limitAmount.subtract(order.getAmount());
            return true;
        }else {
            return false;
        }
    }
}

public class BaiTiaoHandler extends RiskHandler {
    /**
     * 300 限额
     */
    private BigDecimal limitAmount = BigDecimal.valueOf(300);
    public BaiTiaoHandler() {
        super(PayTypeEnum.BAI_TIAO.getPayType());
    }
    @Override
    protected boolean canPay(Order order) {
        if(order.getAmount().compareTo(limitAmount) < 0){
            limitAmount = limitAmount.subtract(order.getAmount());
            return true;
        }else {
            return false;
        }
    }
}

public interface Order {
    /**
     * 获取支付方式
     * @return 支付方式
     */
    String getPayType();
    /**
     * 获取订单金额
     * @return 订单金额
     */
    BigDecimal getAmount();
}

public class ConsumeOrder implements Order {
    private String payType;
    private BigDecimal amount;
    public ConsumeOrder(String payType, BigDecimal amount) {
        this.payType = payType;
        this.amount = amount;
    }
    @Override
    public String getPayType() {
        return this.payType;
    }
    @Override
    public BigDecimal getAmount() {
        return this.amount;
    }
}

public enum  PayTypeEnum {
    /**
     * 花呗
     */
    HUA_BEI("hua_bei"),
    /**
     * 白条
     */
    BAI_TIAO("bai_tiao"),
    /**
     * 信用卡
     */
    CREDIT("credit"),
    ;
    private String payType;
    PayTypeEnum(String payType) {
        this.payType = payType;
    }
    public String getPayType() {
        return payType;
    }
}

public class PayRiskControlService {
    public boolean canPay(Order order){
        // 设置风控
        RiskHandler creditHandler = new CreditHandler();
        RiskHandler huabeiHandler = new HuabeiHandler();
        RiskHandler baiTiaoHandler = new BaiTiaoHandler();
        creditHandler.setNextHandler(huabeiHandler);
        huabeiHandler.setNextHandler(baiTiaoHandler);
        return creditHandler.handler(order);
    }
}

public class Test {
    public static void main(String[] args) {
        // 花呗订单
        ConsumeOrder huabeiOrder = new ConsumeOrder(
                PayTypeEnum.HUA_BEI.getPayType(), BigDecimal.valueOf(200)
        );
        // 白条订单
        ConsumeOrder baitiaoOrder = new ConsumeOrder(
                PayTypeEnum.BAI_TIAO.getPayType(), BigDecimal.valueOf(301)
        );
        // 加载风控系统
        PayRiskControlService riskControlService = new PayRiskControlService();
        // 创建订单
        boolean canPayOfHuabei = riskControlService.canPay(huabeiOrder);
        boolean canPayOfBaitiao = riskControlService.canPay(baitiaoOrder);
        System.out.println("canPayOfHuabei = " + canPayOfHuabei);
        System.out.println("canPayOfBaitiao = " + canPayOfBaitiao);
    }
}