文件变化监视 java.nio.file.WatchService

WatchKey java.nio.file.Path. register(WatchService watcher, Kind<?>... events) throws IOException
为该文件注册watch service。
Registers the file located by this path with a watch service. 

WatchKey java.nio.file.WatchService. take() throws InterruptedException
检索并移除下一个watch key。若没有可检索的则阻塞。
Retrieves and removes next watch key, waiting if none are yet present.

List<WatchEvent<?>> java.nio.file.WatchKey. pollEvents()
检索并移除所有该watch key
Retrieves and removes all pending events for this watch key, returning a List of the events that were retrieved. 

Kind<?> java.nio.file.WatchEvent. kind()
返回事件种类
Returns the event kind.

String java.nio.file.WatchEvent.Kind. name()
返回事件种类的名字。
Returns the name of the event kind.

? java.nio.file.WatchEvent. context()
返回事件发生的环境，简单讲就是不带路径的文件名。
Returns the context for the event.