RxJava引入了Single T.如何转换Observable< T>到单个T?

RxJava最近引入了单.有没有一种方法可以将已经存在的Observable(几乎是Single)转换为Single，而无需修改原始Observable的来源?

RxJava recently introduced Single. Is there a way to convert an already existing Observable (that's pretty much a Single) to a Single without modifying the source of the original observable?

例如，我有一个api服务类，该类的方法返回一个Observable-本质上是从远程资源中获取User.说我无法修改服务.我想在其他地方使用它，但返回一个Single.我该怎么做?

For example, I have an api service class with a method that returns an Observable - which is essentially fetching a User from a remote resource. Say I can't modify the service. I want to consume this elsewhere but return a Single. How do I do this?

更多背景

RxJava最近引入了Single的概念，它或多或少是Rx友好的简单回调(即，可观察的发出一个对象或错误)(在此处了解更多信息-

RxJava recently introduced the concept of a Single which is more or less an Rx friendly simple callback (i.e. an Observable emitting one object or an error) (read more about it here - http://reactivex.io/documentation/single.html)