JSR 203 is a new java I/O milestone, and the most powerful API ever since the JDK first release, which streamlines all java 7 I/O developments, also it makes I/O applications development easy and powerful more than ever. The watch service API introduced in java 7 NIO.2 JSR 203 as thread safe service (which) is capable of watching any object for changes and pushes back these changes for you as event notifications. Watched objects should implement java.nio.file.Watchable interface which is the key interface in this API. All the API classes reside in the "java.nio.file" package. This API is a low level API, which can be used by as it is or you can build your own customized solution that fulfills you requirements. By default it uses the underlying file system features and functionalities to watch registered file system for modification or changes. It allows you to register file, directory or directories to be monitored for different kinds of notification events that you interested in during the registration process. When one or more of registered events are detected by the watch service, it passes the detected events notifications to the process that responsible for handling the registration process through a separate thread or pool of threads........... Read the full article for more.