我是ReactiveX for Java的新手,我有以下代码块来进行外部http调用,但它不是异步的.我们使用的是rxjava 1.2和Java 1.8

  private ResponseEntity<String> callExternalUrl(String url, String json, HttpMethod method) {

    RestTemplate restTemplate;
    HttpEntity request;

      request = new HttpEntity(jsonContent, httpHeaders);

    return restTemplate.exchange(url, httpMethod, request, String.class);

  }

我在网上找到了以下代码块,但我无法理解它以及如何将其应用到我的代码库中.

private RxClient<RxObservableInvoker> httpClient;
public <T> Observable<T> fetchResult(String url, Func1<Response, T> mapper) {

    return httpClient.target(url)
        .request()
        .rx()
        .get()
        .subscribeOn(Schedulers.io())
        .map(mapper);
  }

解决方法:

如果我理解正确,你需要这样的东西来包装你现有的callExternalUrl

static Observable<String> callExternalUrlAsync(String url, String json, HttpMethod method)
{
    return Observable.fromCallable(() -> callExternalUrl(url, json, method))
            .subscribeOn(Schedulers.io())
            .flatMap(re -> {
                         if (re.hasBody())
                             return Observable.just(re.getBody());
                         else
                             return Observable.error(new RuntimeException("Bad response status " + re.getStatusCode()));
                     },
                     e -> Observable.error(e),
                     (Func0<Observable<? extends String>>) (() -> Observable.empty())) // I need explicit cast or it won't compile :-(
            .observeOn(Schedulers.computation());
}

代码简述：

>它计划在Schedulers.io上执行现有的callExternalUrl
> ResponseEntity的最小转换< T>成功的T和错误案例.它也发生在io调度程序上,但它并不重要,因为它非常简短. (如果callExternalUrl中有异常,则按原样传递.)
>使订阅者在Schedulers.computation上执行结果

注意事项：

>您可能希望将自定义调度程序用于subscribeOn和observeOn
>您可能希望在传递给flatMap的第一个lambda中有一些更好的逻辑来区分成功和错误,并且您肯定需要一些更具体的异常类型.

高阶魔术

如果您愿意使用高阶函数并交换一点性能以减少代码重复,您可以执行以下操作：

// Universal wrapper method
static <T> Observable<T> wrapCallExternalAsAsync(Func3<String, String, HttpMethod, ResponseEntity<T>> externalCall, String url, String json, HttpMethod method)
{
    return Observable.fromCallable(() -> externalCall.call(url, json, method))
            .subscribeOn(Schedulers.io())
            .flatMap(re -> {
                         if (re.hasBody())
                             return Observable.just(re.getBody());
                         else
                             return Observable.error(new RuntimeException("Bad response status " + re.getStatusCode()));
                     },
                     e -> Observable.error(e),
                     (Func0<Observable<? extends T>>) (() -> Observable.empty())) // I need explicit cast or it won't compile :-(
            .observeOn(Schedulers.computation());
}

static Observable<String> callExternalUrlAsync_HigherOrder(String url, String json, HttpMethod method)
{
    return wrapCallExternalAsAsync(MyClass::callExternalUrl, url, json, method);
}

MyClass就在你的callExternalUrl的哪个地方.

更新(仅限异步调用)

private static RxClient httpClient = Rx.newClient(RxObservableInvoker.class); //这里你可以传递自定义ExecutorService

private <T> Observable<String> executeHttpAsync(String url, String httpMethod, Entity<T> entity) {
    return httpClient.target(url)
            .request()
            .headers(httpHeaders) // assuming httpHeaders is something global as in your example
            .rx()
            .method(httpMethod, entity)
            .map(resp -> {
                if (200 != resp.getStatus()) {
                    throw new RuntimeException("Bad status code " + resp.getStatus());
                } else {
                    if (!resp.hasEntity()) {
                        // return null; // or error?
                        throw new RuntimeException("Empty response"); // or empty?
                    } else {
                        try {
                            return resp.readEntity(String.class);
                        } catch (Exception ex) {
                            throw new RuntimeException(ex); // wrap exception into unchecked
                        }
                    }
                }
            })
            .observeOn(Schedulers.computation());
}

private Observable<String> executeGetAsync(String url) {
    return executeHttpAsync(url, "GET", null);
}

private Observable<String> executePostAsync(String url, String json) {
    return executeHttpAsync(url, "POST", Entity.json(json));
}

类似的警告同样适用：

>您可能希望将自定义调度程序用于newClient调用和observeOn
>您可能希望有一些更好的错误处理逻辑,而不仅仅是检查它是否是HTTP 200,并且您肯定需要一些更具体的异常类型.但这是所有业务逻辑特定的,所以它取决于您.

此外,从您的示例中还不清楚请求的主体(HttpEntity)是如何构建的,以及您是否真的总是希望String作为响应,就像在原始示例中一样.我仍然按原样复制你的逻辑.如果您需要更多的东西,您可能应该参考https://jersey.java.net/documentation/2.25/media.html#json的文档