java监听文件目录的改变

原文转至：http://marshal.easymorse.com/archives/1617

 JDK 7 oracle 文章地址：http://docs.oracle.com/javase/tutorial/essential/io/notification.html

 

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。

这要等到java 7的出现，见：http://tech.puredanger.com/java7#jsr203，jsr203对io的新扩展中，有：

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：

http://twit88.com/blog/2007/10/02/develop-a-java-file-watcher/

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：

<dependency>
<groupId>com.lightspeedleader</groupId>
<artifactId>directorywatcher</artifactId>
<version>1.0</version>
</dependency>

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

的contextInitialized方法启动文件监听器，通过contextDestroyed方法关闭文件监听器。

有关该监听器的用法，见：

http://tomcat.apache.org/tomcat-5.5-doc/servletapi/javax/servlet/ServletContextListener.html