设计模式实战，工厂+策略+单例解决 if else 过多问题

向右看齐 2022-12-17 05:20 49阅读 0赞

# 场景 #

在支付选择中，可以选择京东白条、支付宝、微信、银联支付等。

public void payment(String payType) { 
    
            if (payType.equals("JD")) { 
                
                //京东支付
                
            } else if (payType.equals("Alibaba")) { 
                //支付宝支付
                
            } else if (payType.equals("Tecent")) { 
                //微信支付
                
            } else if (payType.equals("Union")) { 
                //银联支付 
                
            } else { 
                //其它支付........
    
            }
    
        }

# 解决方案 #

工厂设计模式+策略模式+单例模式，UML图如下：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center]

# 策略 #

public abstract class PaymentStrategy { 
    
    
        public abstract String getName();
    
        protected abstract double queryBalance(String uid);
    
    
        public MsgResult pay(String uid, double amount) { 
            if (queryBalance(uid) < amount) { 
                return new MsgResult(500, "支付失败", "余额不足");
            }
            return new MsgResult(200, "支付成功", "支付余额: " + (queryBalance(uid) - amount));
        }
    
    
    }
    
    public class UnionPayStrategy extends PaymentStrategy { 
        @Override
        public String getName() { 
            return "银联支付";
        }
    
        @Override
        protected double queryBalance(String uid) { 
            return 100;
        }
    }
    
    public class TecentPayStrategy extends PaymentStrategy { 
        @Override
        public String getName() { 
            return "微信支付";
        }
    
        @Override
        protected double queryBalance(String uid) { 
            return 1000;
        }
    }
    
    public class JdPayStrategy extends PaymentStrategy { 
        @Override
        public String getName() { 
            return "京东白条";
        }
    
        @Override
        protected double queryBalance(String uid) { 
            return 1000;
        }
    }
    
    public class AlibabaPayStrategy extends PaymentStrategy { 
    
        @Override
        public String getName() { 
            return "支付宝支付";
        }
    
        @Override
        protected double queryBalance(String uid) { 
            return 1000;
        }
    }

# 枚举 #

public enum PaymentEnum { 
    
    
        ALIBABA("ALIBABA", new AlibabaPayStrategy()),
        JD("JD", new JdPayStrategy()),
        TECENT("TECENT", new TecentPayStrategy()),
        UNION("UNION", new UnionPayStrategy()),
        DEFAULT("DEFAULT", new AlibabaPayStrategy());
    
        private final String payName;
    
        private final PaymentStrategy paymentStrategy;
    
    
        PaymentEnum(String payName, PaymentStrategy paymentStrategy) { 
            this.payName = payName;
            this.paymentStrategy = paymentStrategy;
        }
    
        public String getPayName() { 
            return payName;
        }
    
        public PaymentStrategy getPaymentStrategy() { 
            return paymentStrategy;
        }
    }

# 工厂+单例 #

public class PaymentFactory { 
    
        /** * 注册表 */
        private static Map<String, PaymentStrategy> register = new HashMap<>();
    
        static { 
            for (PaymentEnum p : PaymentEnum.values()) { 
                register.put(p.getPayName(), p.getPaymentStrategy());
            }
        }
    
        /** * 单例+饿汉(注册表) */
        public static PaymentStrategy getInstance(String payType) { 
            if (register.containsKey(payType)) { 
                return register.get(payType);
            }
            return PaymentEnum.DEFAULT.getPaymentStrategy();
        }
    
    
    }

# 业务类 #

@AllArgsConstructor
    @Data
    @NoArgsConstructor
    @ToString
    public class MsgResult { 
    
        private int code;
    
        private Object data;
    
        private String msg;
    
    
    }
    
    
    
    
    @AllArgsConstructor
    @Data
    @NoArgsConstructor
    @ToString
    public class Order { 
    
        private String uid;
    
        private String orderId;
    
        private Double amount;
    
    
        public MsgResult pay(String payType) { 
    
            PaymentStrategy paymentStrategy = PaymentFactory.getInstance(payType);
            System.out.println("欢迎使用" + paymentStrategy.getName());
            System.out.println("本次交易金额为："  + amount + ",....开始扣款");
            return paymentStrategy.pay(uid,amount);
    
        }
    
    }

# 测试类 #

public class PayTest { 
    
        public static void main(String[] args) { 
    
            Order order = new Order("6", "6", 500.0);
            MsgResult msg = order.pay(PaymentEnum.ALIBABA.getPayName());
            System.out.println(msg.toString());
    
        }
    
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center 1]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center]: /images/20221123/b2bd423b7a1742bdb21d95ee792f370b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70_pic_center 1]: /images/20221123/a9798212c72d4d5992066d3e60a5bfcd.png