如何在反应性 Spring WebClient 调用的错误部分抛出异常？

Question

我想要以下方法在发生错误时抛出自定义异常：

@Service
public class MyClass {

    private final WebClient webClient;

    public MatcherClient(@Value("${my.url}") final String myUrl) {
        this.webClient = WebClient.create(myUrl);
    }

    public void sendAsync(String request) {

        Mono<MyCustomResponse> result = webClient.post()
            .header(HttpHeaders.CONTENT_TYPE, "application/json")
            .body(BodyInserters.fromObject(request))
            .retrieve()
            .doOnError(throwable -> throw new CustomException(throwable.getMessage()))
            .subscribe(response -> log.info(response));

    }

}

我还设置了一个单元测试，期望抛出 CustomException。不幸的是，测试失败并且异常被包装到 Mono 对象中。这里还有测试代码供参考：

@Test(expected = CustomException.class)
public void testSendAsyncRethrowingException() {
    MockResponse mockResponse = new MockResponse()
        .setHeader(HttpHeaders.CONTENT_TYPE, "application/json")
        .setResponseCode(500).setBody("Server error");
    mockWebServer.enqueue(mockResponse);

    matcherService.matchAsync(track);
}

我正在使用 MockWebServer 模拟测试中的错误。

那么，如果要使我的方法真正抛出异常，我应该如何实现 doOnError 或 onError 部分？

Answer 1

我没有使用 doOnError，而是改用订阅方法，同时接受错误消费者：

Mono<MyCustomResponse> result = webClient.post()
            .header(HttpHeaders.CONTENT_TYPE, "application/json")
            .body(BodyInserters.fromObject(request))
            .retrieve()
            .subscribe(response -> log.info(response),
                       throwable -> throw new CustomException(throwable.getMessage()));

这份文档很有帮助：https://projectreactor.io/docs/core/release/reference/index.html#_error_handling_operators

Answer 2

我建议从网络客户端公开 API returns Mono<Void> 的反应式 API，特别是如果您将方法命名为 "sendAsync"。如果您必须阻止对 return/fail 的调用，则它不是异步的。如果你想提供一个 sendSync() 替代方案，你总是可以让它调用 sendAsync().block().

对于异常的转换，可以使用专用的onErrorMap运算符。

对于测试，事实是，您不能 100% 测试具有纯命令式和同步结构（如 JUnit 的 Test(expected=?) 注释）的异步代码。（虽然一些反应运算符不会引发并行性，所以这种测试有时可以工作）。

您也可以在此处使用 .block()（测试是不太可能出现问题的罕见情况之一）。

但如果我是你，我会养成使用 reactor-test 中的 StepVerifier 的习惯。举一个总结我的建议的例子：

@Service
public class MyClass {

    private final WebClient webClient;

    public MatcherClient(@Value("${my.url}") final String myUrl) {
        this.webClient = WebClient.create(myUrl);
    }

    public Mono<MyCustomResponse> sendAsync(String request) {
        return webClient.post()
            .header(HttpHeaders.CONTENT_TYPE, "application/json")
            .body(BodyInserters.fromObject(request))
            .retrieve()
            .onErrorMap(throwable -> new CustomException(throwable.getMessage()))
            //if you really need to hardcode that logging
            //(can also be done by users who decide to subscribe or further add operators)
            .doOnNext(response -> log.info(response));
    }
}

和测试：

@Test(expected = CustomException.class)
public void testSendAsyncRethrowingException() {
    MockResponse mockResponse = new MockResponse()
        .setHeader(HttpHeaders.CONTENT_TYPE, "application/json")
        .setResponseCode(500).setBody("Server error");
    mockWebServer.enqueue(mockResponse);

    //Monos are generally lazy, so the code below doesn't trigger any HTTP request yet
    Mono<MyCustomResponse> underTest = matcherService.matchAsync(track);

    StepVerifier.create(underTest)
    .expectErrorSatisfies(t -> assertThat(t).isInstanceOf(CustomException.class)
        .hasMessage(throwable.getMessage())
    )
    .verify(); //this triggers the Mono, compares the
               //signals to the expectations/assertions and wait for mono's completion

}

Answer 3

The retrieve() method in WebClient throws a WebClientResponseException whenever a response with status code 4xx or 5xx is received.

1.您可以使用 onStatus() 方法自定义异常

public Mono<JSONObject> listGithubRepositories() {
 return webClient.get()
        .uri(URL)
        .retrieve()
        .onStatus(HttpStatus::is4xxClientError, clientResponse ->
            Mono.error(new MyCustomClientException())
        )
        .onStatus(HttpStatus::is5xxServerError, clientResponse ->
            Mono.error(new MyCustomServerException())
        )
        .bodyToMono(JSONObject.class);
}

2。通过检查响应状态抛出自定义异常

   Mono<Object> result = webClient.get().uri(URL).exchange().log().flatMap(entity -> {
        HttpStatus statusCode = entity.statusCode();
        if (statusCode.is4xxClientError() || statusCode.is5xxServerError())
        {
            return Mono.error(new Exception(statusCode.toString()));
        }
        return Mono.just(entity);
    }).flatMap(clientResponse -> clientResponse.bodyToMono(JSONObject.class))

参考： https://www.callicoder.com/spring-5-reactive-webclient-webtestclient-examples/

如何在反应性 Spring WebClient 调用的错误部分抛出异常？

How to throw an exception in on error part of reactive Spring WebClient call?

reactive-programming

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spring-webclient

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