通过map+Function优化if else

需求背景

在实际项目中，好比在一个简单的订单处理系统，其中订单有不同的状态（比如新建、已支付、已发货、已收货等），为了实现基于状态机的逻辑处理，我们可以通过switch(状态)去对应不同状态的处理逻辑。

 1  public String process2() {
 2         switch (status) {
 3             case NEW:
 4                 return handleNewOrder();
 5             case PAYMENT_RECEIVED:
 6                 return handlePayment();
 7             case SHIPPED:
 8                 return handleShipment();
 9             case DELIVERED:
10                 return handleDelivered();
11             default:
12                 return "Invalid order";
13         }
14     }

但有种更优雅的做法是通过ImmutableMap<Integer, Function<Object, String>> 的方式去实现。

 1 public static final ImmutableMap<OrderStatus , Function<Order, String>> STATUS_HANDLERS =
 2             ImmutableMap.<OrderStatus, Function<Order, String>>builder()
 3                     .put(OrderStatus.NEW, Order::handleNewOrder)
 4                     .put(OrderStatus.PAYMENT_RECEIVED, Order::handlePayment)
 5                     .put(OrderStatus.SHIPPED, Order::handleShipment)
 6                     .put(OrderStatus.DELIVERED, Order::handleDelivered)
 7                     .build();
 8 
 9     public String process() {
10         Function<Order, String> handler = STATUS_HANDLERS.get(status);
11         if (handler == null) {
12             return "Invalid order";
13         }
14         return handler.apply(this);
15     }

完整代码如下

订单状态枚举

 1 public enum OrderStatus {
 2     /**
 3      * 新建
 4      * 已付款
 5      * 已发货
 6      * 已收货
 7      */
 8     NEW,
 9     PAYMENT_RECEIVED,
10     SHIPPED,
11     DELIVERED
12 }

订单类

 1 @Data
 2 public class Order {
 3     private final String orderId;
 4     private final OrderStatus status;
 5 
 6     public Order(String orderId, OrderStatus status) {
 7         this.orderId = orderId;
 8         this.status = status;
 9     }
10 
11     public static final ImmutableMap<OrderStatus , Function<Order, String>> STATUS_HANDLERS =
12             ImmutableMap.<OrderStatus, Function<Order, String>>builder()
13                     .put(OrderStatus.NEW, Order::handleNewOrder)
14                     .put(OrderStatus.PAYMENT_RECEIVED, Order::handlePayment)
15                     .put(OrderStatus.SHIPPED, Order::handleShipment)
16                     .put(OrderStatus.DELIVERED, Order::handleDelivered)
17                     .build();
18 
19     public String process() {
20         Function<Order, String> handler = STATUS_HANDLERS.get(status);
21         if (handler == null) {
22             return "Invalid order";
23         }
24         return handler.apply(this);
25     }
26 
27     public String process2() {
28         switch (status) {
29             case NEW:
30                 return handleNewOrder();
31             case PAYMENT_RECEIVED:
32                 return handlePayment();
33             case SHIPPED:
34                 return handleShipment();
35             case DELIVERED:
36                 return handleDelivered();
37             default:
38                 return "Invalid order";
39         }
40     }
41 
42     private String handleNewOrder() {
43         // Handle new order logic here
44         return "Order " + orderId + " 新建";
45     }
46 
47     private String handlePayment() {
48         // Handle payment logic here
49         return "Order " + orderId + " 已支付";
50     }
51 
52     private String handleShipment() {
53         // Handle shipment logic here
54         return "Order " + orderId + " 已发货";
55     }
56 
57     private String handleDelivered() {
58         // Handle delivered logic here
59         return "Order " + orderId + " 已收获";
60     }
61 
62     public static void main(String[] args) {
63         Order order = new Order("12345", OrderStatus.SHIPPED);
64         //if else方式
65         String result2 = order.process2();
66         //map + Function的方式
67         String result = order.process();
68 
69         System.out.println(result);
70         System.out.println(result2);
71     }
72 }

运行结果