轮询文件以进行更改？ [英] Poll a file for change?

问题描述

这是一个模式，我希望轮询一个文件的变化（当它上次写）。当文件确实从以前的值改变，我希望执行一些功能。

 （poll-for-changes file-str on-change-fx current-value）
  

其中

1. code> file-str 只是一个指定文件位置的字符串


2. on-change-fx 是当 file-str 的文件更改时应调用的函数。让我们说， on-change-fx 应该使用指向 file-str 的File对象作为参数。


3. current-value 文件的当前值（以毫秒为单位）。您可以设置为0，以保证此函数至少运行一次，或者设置为实际值，以便在实际检测到更改时只运行此函数。

我只是希望这个函数以最清晰，最简洁，Clojurist的方式实现。谢谢。

解决方案

如果你想轮询一个目录或文件并执行它，我认为 watchtower 相当不错。

Java 7有一个WatchService，它使用文件系统事件来响应更改。在这种情况下，您不会轮询，但阻止未来的文件事件。我不认为在Clojure有任何项目利用这一点，虽然我花了一些时间与它一起写一个小图书馆。其来源在这里 p>

我不声称我的库甚至是完整的，但它确实使用Java 7服务，所以你可以使用它为自己的项目的灵感。

It is often a pattern that I wish to poll a file for changes (when it was last written). When the file does change from its previous value, I wish to execute some function. Something of the form.

(poll-for-changes file-str on-change-fx current-value)

where

1. file-str is just a string that specifies the files location
2. on-change-fx is the function that should be called when the file at file-str changes. Let us say that the on-change-fx should take the File object pointing to file-str as a argument.
3. current-value the current value of the file in milliseconds. You might set to 0 to guarantee that this function will run at least once, or to the actual value to only run this function when you actually detect a change.

I would just like this function implemented in the clearest, most concise, Clojurist way possible. Thank you.

解决方案

If you're looking to poll a directory or files and act on it, I think watchtower is pretty good to look at.

Java 7 has a WatchService, which uses file system events to react to changes. In this case, you don't poll at all, but block on a future file event. I don't think there are any projects in Clojure that are out there leveraging that, although I spent some time toying with it to write a small library. The source for it is here

I don't claim my library is even complete, but it does use the Java 7 service, so you could use that for inspiration on your own project.

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