return 如何直接从 Uni<T> 中获取值而不将其转换为 CompletableFuture

Question

给个上下文，我在我的class中有两个方法都是returns Uni，其中第一个方法以如下方式依赖于第二个方法

public Uni<String> greeting(String name) {
    log.info("\n\n");
    log.info("\t`greeting(String name)` Executing on Thread {}",Thread.currentThread().getName());

    return Uni
            .createFrom()
            .item(name) //synchronous now imagine you have retrieve a value from an I/O call you will have to pass a supplier, ref README.md#Links.1
            .emitOn(emitExecutor)
            .onItem()
            .transform(parameter-> {
                log.debug("`(p)>Transform` invoked on Thread {}",Thread.currentThread().getName());
                assert Thread.currentThread().getName().equals(threadName);
                try {
                    return ioSimulation(parameter,Thread.currentThread().getName()).subscribeAsCompletionStage().get();
                } catch (InterruptedException | ExecutionException e) {
                    log.error("failed to execute ioSimulation due to {}",e.getMessage());
                    throw new RuntimeException("failed to communicate with client {}"+e.getMessage());
                }
            }).onFailure()
            .retry() 
    .atMost(2);
}


public Uni<String> ioSimulation(String param,String threadName){
        log.debug("`ioSimulation(String param)` Executing on Thread {}",Thread.currentThread().getName());
        assert Thread.currentThread().getName().equals(threadName);
        return MockServer.client
                .getAbs("http://localhost:80")
                .addQueryParam("name",param)
                .send()
                .onItem().transform(response-> {
                    if (response.statusCode() == 200){
                        return response.bodyAsString();
                    }else{
                        throw  new IllegalStateException(response.bodyAsString());
                    }
        });

现在在 greeting(String name)（第一个）方法中 return 我必须使用 subscribeAsCompletionStage().get() 的字符串值，否则 return 类型将是 Uni<Uni<String>>.

我的问题如下

是一种方法，我可以在不使用 subscribeAsCompletionStage().get() 的情况下 return 第二种方法 ioSimulation 的实际结果（包裹在 Uni 中的精确值）如果是，那我怎么能这样做吗？
这样做有什么更好的办法吗？比如重构现有的方法。

如果有人感兴趣，可以找到完整的代码here

Answer 1

感谢@Ladicek，有一种开箱即用的方法可以在 transform 块中处理异步 Uni<T> return，解决方案是

public Uni<String> greeting(String name) {
    log.info("\n\n");
    log.info("\t`greeting(String name)` Executing on Thread {}",Thread.currentThread().getName());

    return Uni
            .createFrom()
            .item(name) //synchronous now imagine you have retrieve a value from an I/O call you will have to pass a supplier, ref README.md#Links.1
            .emitOn(emitExecutor)
            .onItem()
            .transformToUni(parameter -> ioSimulation(parameter,Thread.currentThread().getName()))
            .onFailure()
            .retry()
    .atMost(2);

}


public Uni<String> ioSimulation(String param,String threadName){
    log.debug("`ioSimulation(String param)` Executing on Thread {}",Thread.currentThread().getName());
    assert Thread.currentThread().getName().equals(threadName);
    return MockServer.client
            .getAbs("http://localhost:80")
            .addQueryParam("name",param)
            .send()
            .onItem().transform(response-> {
                if (response.statusCode() == 200){
                    return response.bodyAsString();
                }else{
                    throw  new IllegalStateException(response.bodyAsString());
                }
    });

}

transformToUni 异步转换接收到的项目并 return 生成一个新的 Uni<T>

更新：

另一种方法（我正在寻找的方法）是使用回调。

public Uni<String> callbackGreeting(String name) {
    log.info("\n\n");
    log.info("\t`callbackGreeting(String name)` Executing on Thread {}", Thread.currentThread().getName());

    return Uni
            .createFrom()
            .item(name) //synchronous now imagine you have retrieve a value from an I/O call you will have to pass a supplier, ref README.md#Links.1
            .emitOn(emitExecutor)
            .onItem()
            .transformToUni(param -> {
                return Uni.createFrom().emitter(em -> {
                    ioSimulation(param, Thread.currentThread().getName())
                            .subscribe()
                            .with(success -> em.complete(success.bodyAsString()), //putting result of uni ioSimulation into the callback
                                    exception -> {
                                        log.info("the following error occurred before sending to em.complete {}", exception.getMessage());
                                        em.fail(exception);
                                    });

                });
            })
            .onFailure()
            .retry()
            .atMost(2)
            .map(item -> "Operation completed with item " + item);

}

此示例仅用于演示目的，我知道这不是最佳解决方案。完整代码为here

return 如何直接从 Uni<T> 中获取值而不将其转换为 CompletableFuture

how can one return a value directly from Uni<T> without converting that into a CompletableFuture

java

reactive-programming

quarkus

smallrye

mutiny