How To Monitor Win32 File System Changes in Java (300605)

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In this section, you create a Java application that monitors the file system for file name changes. The Java application code uses the Microsoft Java Delegate mechanism to create a simple event that is named fileEvent. This event is triggered by the underlying file system events. The code creates a Java Console application that creates a thread to monitor the file system. This thread displays messages in the Java Console window when a file change notification event is triggered.

1. Create a new Console application project named Class1.java in Visual J++ 6.0.
2. Replace the default Class1 code that Visual J++ generates with the following code:

   import com.ms.wfc.core.*;
   
   public class Class1
   {
   	public static void main (String[] args) {
   		Class1 c = new Class1();
   		c.start();
   	}
   	
   	public void start() {
   		System.out.println("Starting Thread");
   		FileSystemCtrl f = new FileSystemCtrl();
   		f.addOnFileSystemEvent(new EventHandler(this.fileEvent));
   		f.run();
   	}
   	
   	public void fileEvent(Object source, Event e) {
   		System.out.println("FileEvent Handled");
   	}
   }
   
   class FileSystemCtrl extends Thread {
   	EventHandler fileEventDelegate = null;
   	public void run() {
   		int[] handles = new int[1];
   		handles[0] = com.ms.win32.Kernel32.FindFirstChangeNotification("c:\\",true,com.ms.win32.winf.FILE_NOTIFY_CHANGE_FILE_NAME);
   		
   		while(true) {
   			int waitStatus = com.ms.win32.Kernel32.WaitForMultipleObjects(handles.length,handles,false,com.ms.win32.wini.INFINITE);
   			
   			switch(waitStatus) {
   			case com.ms.win32.winw.WAIT_OBJECT_0:
   				OnFileSystemEvent(new Event());
   				com.ms.win32.Kernel32.FindNextChangeNotification(handles[0]);
   				break;
   			}
   		}
   	}
   	
   	public final void addOnFileSystemEvent(EventHandler handler) {
   		fileEventDelegate = (EventHandler)com.ms.lang.Delegate.combine(fileEventDelegate,handler);
   	}
   	protected void OnFileSystemEvent(Event event) {
   		if(fileEventDelegate!=null){
   			fileEventDelegate.invoke(this,event);
   		}
   	}
   } 
   					

3. Save Class1.java.
4. At a command prompt, run the following commands (which use the tools in the Microsoft Software Development Kit for Java) to build and to execute the code:

   jvc /nomessage /x- class1.java
   start jview class1

5. Click Start, and then click Run.
6. Type Notepad C:\Test.txt, and then click OK.
7. When you are prompted to create a new file, click OK. Notice that the following message appears in the Java Console window:

   FileEvent Handled