项目反应堆.Mono.map() 与 Mono.flatMap() [英] Project Reactor. Mono.map() vs Mono.flatMap()

问题描述

就Mono 而言，它们之间的主要区别是什么?从文档中，我读到 flatMap 是异步的，而 map 是同步的.但这对我来说并没有真正意义 b/c Mono 是关于并行性的，这一点是不可理解的.有人可以用更容易理解的方式重新表述它吗?

What is the principal difference between these in terms of Mono? From the documentation, I read that flatMap acts asynchronous and map synchronous. But that doesn't really make sense for me b/c Mono is all about parallelism and that point isn't understandable. Can someone rephrase it in a more understandable way?

然后在 flatMap 的文档中说明 (https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#flatMap-java.util.function.功能-):

Then in the documentation for flatMap stated (https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#flatMap-java.util.function.Function-):

Transform the item emitted by this Mono asynchronously, returning the 
value emitted by another Mono (possibly changing the value type).

另一个 Mono 是什么意思?

Which another Mono is meant there?

推荐答案

Mono#flatMap 使用 Function 将一个值转换为另一个 Mono>.Mono 可以代表一些异步处理，例如 HTTP 请求.

Mono#flatMap takes a Function that transforms a value into another Mono. That Mono could represent some asynchronous processing, like an HTTP request.

另一方面，Mono#map 接受一个 Function 将 T 类型的值转换为另一个值，即输入 R.因此，该转换是命令式和同步完成的(例如，将 String 转换为 URL 实例).

On the other hand, Mono#map takes a Function that transforms a value of type T into another value, of type R. That transformation is thus done imperatively and synchronously (eg. transforming a String into an URL instance).

flatMap 的另一个微妙之处是操作符订阅生成的 Mono，这与将相同的 Function 传递给地图.

The other subtlety with flatMap is that the operator subscribes to the generated Mono, unlike what would happen if you passed the same Function to map.

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