Spring webflux "Only one connection receive subscriber allowed" if return 来自 switchIfEmpty 的服务器响应

Question

我想举个例子，如果对象存在则发送错误，如果不存在则创建新用户。

这是我的处理程序：

public Mono<ServerResponse> createUser(ServerRequest request) {
        Mono<UserBO> userBOMono = request.bodyToMono(UserBO.class);
        Mono<String> email = userBOMono.map(UserBO::getEmail);
        Mono<User> userMono = email.flatMap(userRepository::findByEmail);
        return userMono.flatMap(user -> {
            Mono<ErrorResponse> errorResponseMono = errorHanlder.handleEmailAlreadyExist();
            return ServerResponse.status(HttpStatus.CONFLICT)
                    .contentType(MediaType.APPLICATION_JSON)
                    .body(errorResponseMono, ErrorResponse.class);
        }).switchIfEmpty(Mono.defer(() -> {
            Mono<User> newUserMono = userBOMono.flatMap(userMapping::mapUserBOToUser);
            Mono<User> dbUserMono = newUserMono.flatMap(userRepository::save);
            return ServerResponse.status(HttpStatus.CREATED)
                    .contentType(MediaType.APPLICATION_JSON)
                    .body(dbUserMono, User.class);

        }));

如果 Mono 不为空则其 return 与我想要的冲突如果为空则创建新的但它抛出以下错误：

java.lang.IllegalStateException: Only one connection receive subscriber allowed.
    at reactor.ipc.netty.channel.FluxReceive.startReceiver(FluxReceive.java:276) ~[reactor-netty-0.7.8.RELEASE.jar:0.7.8.RELEASE]
    at reactor.ipc.netty.channel.FluxReceive.lambda$subscribe(FluxReceive.java:127) ~[reactor-netty-0.7.8.RELEASE.jar:0.7.8.RELEASE]
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute$$$capture(AbstractEventExecutor.java:163) ~[netty-common-4.1.27.Final.jar:4.1.27.Final]
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java) ~[netty-common-4.1.27.Final.jar:4.1.27.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404) ~[netty-common-4.1.27.Final.jar:4.1.27.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:464) ~[netty-transport-4.1.27.Final.jar:4.1.27.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor.run(SingleThreadEventExecutor.java:884) ~[netty-common-4.1.27.Final.jar:4.1.27.Final]
    at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_131]

更新说明：根据方法定义的正确行为：

switchIfEmpty(Mono<? extends T> alternate)
Fallback to an alternative Mono if this mono is completed without data

意味着当我在 body 中发送空的 Mono 时它工作正常：

return ServerResponse.status(HttpStatus.CREATED)
                    .contentType(MediaType.APPLICATION_JSON)
                    .body(Mono.empty(), User.class);

如果我想从中发送 Mono 对象作为 return，那么处理 swtichIfEmpty 情况的解决方案是什么。

Answer 1

我假设您使用 WebClient 来调用此 API。客户端不应多次订阅，否则会出现此错误。

Answer 2

我终于解决了这个问题，我两次读取 userBOMono 流导致 webflux 抛出这个错误。

所以这是更新后的代码，可以正常工作。

 public Mono<ServerResponse> createUser(ServerRequest request) {
        Mono<UserBO> userBOMono = request.bodyToMono(UserBO.class);
        return userBOMono.flatMap(userBO -> {
            String email = userBO.getEmail();
            Mono<User> userMono = userRepository.findByEmail(email);
            return userMono.flatMap(user -> errorHandler.handleEmailAlreadyExist())
                    .switchIfEmpty(Mono.defer(() -> createNewUser(userBO)));
        });
    }

    private Mono<ServerResponse> createNewUser(UserBO userBO) {
        Mono<User> userMono = Mono.just(userBO).flatMap(userMapping::mapUserBOToUser).flatMap(userRepository::save);
        return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON)
                .body(userMono, User.class);

    }

Spring webflux "Only one connection receive subscriber allowed" if return 来自 switchIfEmpty 的服务器响应

Spring webflux "Only one connection receive subscriber allowed" if return server response from switchIfEmpty

spring

spring-boot

project-reactor

spring-webflux