Watch for file updates

You would read the file(s) in a continuos loop, saving the contents of each file in separate temporary variable. When, after a reading a file, the new content and the temporary content do not match, then the text file has changed. This is just a line of thought which you can make your code work first before putting efficiency int it.

ARTHUR

Jamwaa at 2007-7-12 18:14:40 >

You gotta create a Thread which will monitor the files for you. You detect any changes by comparing the last modified time value for every file you are watching. Whenever this value is updated to a more recent value, then you know there are some changes to read from that file. You can implement an EventListener which will allow for interested classes to register for this event.

Finally, make sure you put your Thread to sleep after every check for something like 500ms so that it doesn't eat your CPU.

Dalzhima at 2007-7-12 18:14:40 >

> I did a folder watcher before using Thread object.

> The thread method is a resource hog. The

> javax.swing.Timer method is better.

Yep. They brought timers into Java for requirements like this.

Threads should only be used when you need concurrency, here you don't.

_helloWorld_a at 2007-7-12 18:14:40 >

This program watches for file updates in a folder

/*

* Main.java

*

* Created on Jun 5, 2007, 2:05:14 PM

*

* To change this template, choose Tools | Template Manager

* and open the template in the editor.

*/

package forumtester;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileReader;

import javax.swing.JOptionPane;

import javax.swing.Timer;

import javax.swing.UIManager;

public class Main

{

// A directory that the change is to be detected

static String folderToWatch = "C:\\";

private static File file = new File(folderToWatch);

// An array to hold the list of files in the directory above

private static String[] listOfFiles;

public static void main(String[] args) throws Exception

{

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

// Popilate the array

listOfFiles = file.list();

// Inner class that does the actual detection

class ChangeListener implements ActionListener

{

public void actionPerformed(ActionEvent event)

{

// After the delay specified by the timer constructor, check on what files are currently

// In the folder and store the value in a new array

String[] newListOfFiles = file.list();

System.gc();

// If the size of the new array is larger than the old array, a new file is detected

if(newListOfFiles.length > listOfFiles.length)

{

// This is the StringBuffer object to hold the contents of the file

StringBuffer text = new StringBuffer();

// I dont know if this is always the case, but is has worked quite perfectly

// The new file is the last item of the NEW array

String nameOfNewFile = newListOfFiles[newListOfFiles.length - 1];

System.out.println("New file detected: " + nameOfNewFile);

try

{

// This is to read the contents of the new file and hold them in the String object declared above

File inputFile = new File(folderToWatch + file.separator + nameOfNewFile);

FileReader in = new FileReader(inputFile);

BufferedReader buff= new BufferedReader(in);

String line; // <<-- added

while ((line = buff.readLine()) != null) //

{

text.append(line).append('\n'); //

}

in.close();

// Finally display the name of the new file in a JOptionPane

JOptionPane.showMessageDialog(null, inputFile.getAbsolutePath(), "New file",

JOptionPane.INFORMATION_MESSAGE);

}

catch (Exception e)

{

JOptionPane.showMessageDialog(null, e, "Error", JOptionPane.ERROR_MESSAGE);

}

// Then set the old array to be equal to the new array so as to be able to detect new files

listOfFiles = newListOfFiles;

}

else

{

System.gc();

}

}

}

// Timer with 1 second (1000 millisecond) loop

Timer t = new Timer(1000, new ChangeListener());

t.start();

// The program will run in a continuous loop till you quit

JOptionPane.showMessageDialog(null, "Quit?");

System.exit(0);

}

}

Jamwaa at 2007-7-12 18:14:40 >