這章節將會運用Spring WebFlux來實作REST API的功能。

引入以下dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

SpringMVC的endpoint method:

@RestController
@RequestMapping(path="/api/orders", produces="application/json")
@CrossOrigin(origins="*")
public class OrderController {
...
  @GetMapping(params="recent")
  public Iterable<Order> recentOrders() {
    PageRequest page = PageRequest.of(0, 12, Sort.by("createdAt").descending());
    return orderRepo.findAll(page).getContent();
  }
...
}

運用WebFlux，將回傳的Iterable改為Flux:

@GetMapping(params="recent")
public Flux<Order> recentOrders() {
  return Flux.fromIterable(orderRepo.findAll()).take(12);
}

不過可以發現，在orderRepo還是運用了原來的方法，也可以直接在repository中改成reactive programming，就會變成:

@GetMapping(params="recent")
public Flux<Order> recentOrders() {
  return orderRepo.findAll().take(12);
}

現在來改寫一下orderById:

@GetMapping("/{id}")
public Order orderById(@PathVariable("id") Long id) {
  Optional<Order> optOrder = orderRepo.findById(id);
  if (optOrder.isPresent()) {
    return optOrder.get();
  }
  return null;
}

可以改為:

@GetMapping("/{id}")
public Mono<Order> orderById(@PathVariable("id") Long id) {
  return orderRepo.findById(id);
}

Spring MVC的postOrder:

@PostMapping(consumes="application/json")
@ResponseStatus(HttpStatus.CREATED)
public Order postOrder(@RequestBody Order order) {
  return orderRepo.save(order);
}

改成reactive:

@PostMapping(consumes = "application/json")
@ResponseStatus(HttpStatus.CREATED)
public Mono<Order> postOrder(@RequestBody Mono<Order> orderMono) {
  return orderRepo.saveAll(orderMono).next();
}

也可如下寫:

@PostMapping(consumes = "application/json")
@ResponseStatus(HttpStatus.CREATED)
public Mono<Order> postOrder(@RequestBody Mono<Order> orderMono) {
  return orderMono.flatMap(orderRepo::save);
}