获取返回mono.empty（）的mono/flux的行号

Question

        Mono.just("data")
                .flatMap(t -> {
                    if (System.currentTimeMillis() % 2 == 0) {
                        return Mono.empty();
                    }
                    return Mono.just("happy1");
                })
                .flatMap(t -> {
                    if (System.currentTimeMillis() % 2 == 0) {
                        return Mono.empty();
                    }
                    return Mono.just("happy2");
                })
                .map(s -> {
                    return "successful complete: " + s;
                })
        .switchIfEmpty(Mono.fromCallable(() -> {
            return "how did I get here?";
        }))
        .block();

Answer 1

由于flux和mono的动态性，以及oncomplete信号被认为足够中性，因此通常只是通过，因此没有通用的解决方案。

在您的特定示例中，可以将mono.empty()替换为mono.empty().dooncomplete(()->/*log something*/)。您甚至可以直接在if块中执行日志记录，但是修饰的空技巧可能适用于更多的情况。

另一种可能是将空变为错误，而不是打开onComplete信号。错误不那么中立，因此有方法来丰富它们以用于调试目的。例如，在每个flatMap后面有一个.checkpoint（“FlatMapX”）语句，您将获得额外的stacktrace部分，这些部分将指向由于空而失败的flatMap。

static final String PARSEABLE_MARKER = "PARSEABLE MARKER: <";
static final char MARKER_END = '>';

String parseLocation(Exception e) {
    StringWriter sw = new StringWriter();
    PrintWriter pw = new PrintWriter(sw);
    e.printStackTrace(pw);

    String trace = sw.toString();
    int start = trace.indexOf(PARSEABLE_MARKER);
    if (start > 0) {
        trace = trace.substring(start + PARSEABLE_MARKER.length());
        trace = trace.substring(0, trace.indexOf(MARKER_END));
        return trace;
    }
    return "I don't know";
}

String testInner() {
    Random random = new Random();
    final boolean first = random.nextBoolean();

    return Mono.just("data")
            .flatMap(t -> {
                if (System.currentTimeMillis() % 2 == 0 && first) {
                    return Mono.empty();
                }
                return Mono.just("happy1");
            })
            .single()
            .checkpoint(PARSEABLE_MARKER + "the first flatMap" + MARKER_END)
            .flatMap(t -> {
                if (System.currentTimeMillis() % 2 == 0 && !first) {
                    return Mono.empty();
                }
                return Mono.just("happy2");
            })
            .single()
            .checkpoint(PARSEABLE_MARKER + "the second flatMap" + MARKER_END)
            .map(s -> {
                return "successful complete: " + s;
            })
            .onErrorResume(NoSuchElementException.class, e ->
                    Mono.just("how did I get here? " + parseLocation(e)))
            .block();
}

    @Test
void test() {
    int successCount = 0;
    int firstCount = 0;
    int secondCount = 0;
    for (int i = 0; i < 100; i++) {
        String message = testInner();
        if (message.startsWith("how")) {
            if (message.contains("first")) {
                firstCount++;
            }
            else if (message.contains("second")) {
                secondCount++;
            }
            else {
                System.out.println(message);
            }
        }
        else {
            successCount++;
        }
    }
    System.out.printf("Stats: %d successful, %d detected first, %d detected second", successCount, firstCount, secondCount);
}

Stats: 85 successful, 5 detected first, 10 detected second