reactive-programming - 如何在响应式(Reactive) Spring WebClient 调用的错误部分抛出异常？

Question

如果发生错误，我希望以下方法抛出自定义异常:

@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，测试失败了，并且 Exception 被包装到了 Mono 对象中。这里还有测试代码供引用:

@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，如果调用时我应该如何实现 doOnError 或 onError 部分才能使我的方法真正抛出异常？

Answer 1

我建议公开一个返回 Mono<Void> 的响应式(Reactive) API来自网络客户端，特别是如果您将方法命名为“sendAsync”。如果您必须阻止调用返回/失败，则它不是异步的。如果您想提供sendSync()或者，您可以随时调用 sendAsync().block() .

对于异常的转换，可以使用专用的onErrorMap运算符。

对于测试，问题是，您无法使用纯命令式和同步构造(如 JUnit 的 Test(expected=?) 注释)100% 测试异步代码。 (尽管一些响应式(Reactive)运算符不会引发并行性，因此这种测试有时可以工作)。

您还可以使用.block()此处(测试是极少数情况之一，这不太可能出现问题)。

但如果我是你，我会养成使用 StepVerifier 的习惯来自reactor-test 。举一个例子来总结我的建议:

@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

}