目前为止，java没有提供自带的对文件目录改变的监听器。使用java自带的(如果是native的就更好了)会方便很多。

A new filesystem interface that supports bulk access to file attributes, change notification, …

但是，目前一般的做法还是自己启动线程定时监控变化。带来的问题是目录文件和嵌套过多的时候性能会下降。

网上有一个现成的解决方案，提供了源代码下载：

可以简单的调用该类库，以下是每5秒钟监控一下指定目录的变化的示例：

public static void main(String[] args) {

// Monitor c:/temp every 5 seconds

DirectoryWatcher dw = new DirectoryWatcher(“c:/temp/”, 5);

dw.addListener(new FileListener());

dw.start();

其中的FileListener就是自定义的文件监听器。需要实现接口：

com.lightspeedleader.directorywatcher.IFileListener

可实现的方法包括：

/**

* Monitoring has just started on this new resource.

*

* @param monitoredResource the resource now being monitored.

*/

public void onStart(Object monitoredResource);

/**

* Monitoring has just ended on this new resource.

*

* @param notMonitoredResource the resource not being monitored anymore.

*/

public void onStop(Object notMonitoredResource);

/**

* Something has been added to this resource, or the resource itself has

* been added.

*

* @param newResource the new resource

*/

public void onAdd(Object newResource);

/**

* The resource has been changed.

*

* @param changedResource the changed resource

*/

public void onChange(Object changedResource);

/**

* Something has been added to this resource, or the resource itself has

* been added.

*

* @param deletedResource the deleted resource

*/

public void onDelete(Object deletedResource);

}

作者也给出了一个简单的实现：

public class FileListener extends BaseListener implements IFileListener {

/**

* Connstructor

*/

public FileListener() {

super();

}

public void onStart(Object monitoredResource) {

// On startup

if (monitoredResource instanceof File) {

File resource = (File) monitoredResource;

if (resource.isDirectory()) {

System.out.println(“Start to monitor ” + resource.getAbsolutePath());

/*File[] files = resource.listFiles();

for (int i = 0; i < files.length; i++) {

File f = (File) files[i];

onAdd(f);

}*/

}

}

}

public void onStop(Object notMonitoredResource) {

}

public void onAdd(Object newResource) {

if (newResource instanceof File) {

File file = (File) newResource;

if (file.isFile()) {

System.out.println(file.getAbsolutePath() + ” is added”);

}

}

}

public void onChange(Object changedResource) {

if (changedResource instanceof File) {

File file = (File) changedResource;

if (file.isFile()) {

System.out.println(file.getAbsolutePath() + ” is changed”);

}

}

}

public void onDelete(Object deletedResource) {

if (deletedResource instanceof String) {

String deletedFile = (String) deletedResource;

System.out.println(deletedFile + ” is deleted”);

}

}

}

为了使用方便，将该源代码未作任何改动，部署到个人的repository上，可在maven中引用：

com.lightspeedleader

directorywatcher

1.0

监听器程序启动线程监控目录，如果不再使用，应该予以关闭：

dw.stop();

如果是在web系统中使用，应该通过web应用监听器：

javax.servlet.ServletContextListener

有关该监听器的用法，见：