使用 WebClient 进行非阻塞调用时方法的返回值策略

import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
import com.google.gson.JsonObject;
import com.google.gson.Gson;
import java.util.List;

public class WebClientExample {

    private final String saveUrl = "http://example.com/save";
    private final String tokenUrl = "http://example.com/token";

    public Mono<Void> save(String body) {
        WebClient client = WebClient.create(saveUrl);
        Mono<String> response = client.post()
                .accept(MediaType.APPLICATION_FORM_URLENCODED)
                .contentType(MediaType.APPLICATION_FORM_URLENCODED)
                .body(BodyInserters.fromFormData("body", body)) // 使用 BodyInserters.fromFormData
                .retrieve()
                .bodyToMono(String.class);

        return response.doOnNext(responseBody -> System.out.println("Successful save message: " + responseBody))
                .then(); // 返回 Mono<Void>
    }

    public Mono<String> getToken(String message) {
        WebClient client = WebClient.create(tokenUrl);
        Mono<String> responseText = client.post()
                .accept(MediaType.APPLICATION_FORM_URLENCODED)
                .contentType(MediaType.APPLICATION_FORM_URLENCODED)
                .body(BodyInserters.fromFormData("message", message)) // 使用 BodyInserters.fromFormData
                .retrieve()
                .bodyToMono(String.class)
                .retry(3);

        return responseText.flatMap(responseBody -> {
            String token = getTokenFromResponse(responseBody);
            return saveService(message, token).thenReturn(token); // 返回 Mono<String>
        });
    }

    private String getTokenFromResponse(String responseBody) {
        JsonObject jsonObject = new Gson().fromJson(responseBody, JsonObject.class);
        return jsonObject.get("access_token").getAsString();
    }

    public Mono<Void> saveService(String message, String accessToken) {
        WebClient client = WebClient.builder()
                .baseUrl(saveUrl)
                .defaultHeaders(httpHeaders -> {
                    httpHeaders.setAccept(List.of(MediaType.APPLICATION_JSON));
                    httpHeaders.setContentType(MediaType.APPLICATION_JSON);
                    httpHeaders.setBearerAuth(accessToken);
                })
                .build();

        return client.post()
                .body(BodyInserters.fromValue(message)) // 使用 BodyInserters.fromValue
                .retrieve()
                .toBodilessEntity()
                .then(); // 返回 Mono<Void>
    }

    public static void main(String[] args) {
        WebClientExample example = new WebClientExample();
        example.getToken("test message")
                .subscribe(
                        token -> System.out.println("Token received: " + token),
                        error -> System.err.println("Error: " + error.getMessage())
                );

        // 保持程序运行一段时间，以便异步操作完成
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}