How can I continously check to see if the text inside a text file has changed to empty? Java

Question

I have the following code in which I want to read what is in the text file and display in textField2 weather it has changed or not... If it has, then I need it to continue. If it hasn't, then I need it to check again until the file has been changed to empty. Can anyone help? Here is my code:

package application;

import javafx.event.ActionEvent;
import javafx.scene.control.TextField;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.Parent;
import javafx.fxml.FXMLLoader;
import javafx.fxml.FXML;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;


public class Main extends Application {
 @Override
 public void start(Stage primaryStage) {
  try {
   // BorderPane root = new BorderPane();
   Parent root = FXMLLoader.load(getClass().
     getResource("Root.fxml"));
   
   Scene scene = new Scene(root,550,400);
   scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
   primaryStage.setScene(scene);
   primaryStage.show();
  } catch(Exception e) {
   e.printStackTrace();
  }
 }
 
 public static void main(String[] args) {
  launch(args);
 }
 
 @FXML
 private TextField textField;
 
 @FXML
 private TextField textField2;
 
 @FXML
 protected void onClick(ActionEvent event) throws IOException  {
        BufferedWriter writer = null;
        try {
            //create a temporary file


            // This will output the full path where the file will be written to...


            writer = new BufferedWriter(new FileWriter("C:/Users/Custom/Documents/Sample.txt"));
            writer.write(textField.getText());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                // Close the writer regardless of what happens...
                writer.close();
            } catch (Exception e) {
            }
            while (readFile("C:/Users/Custom/Documents/Sample.txt") != ""){
             textField2.setText("Waiting...");
            }
            textField2.setText("Done!");
            

 }
}

 String readFile(String fileName) throws IOException {
     BufferedReader br = new BufferedReader(new FileReader(fileName));
     try {
         StringBuilder sb = new StringBuilder();
         String line = br.readLine();

         while (line != null) {
             sb.append(line);
             sb.append("\n");
             line = br.readLine();
         }
         return sb.toString();
     } finally {
         br.close();
     }
 }
}

you can check the time stamp of file to determine whether it has changed or not. and when do you want it to return empty string?? specify the condition — Boola, Jun 24 '16 at 05:12
your loop will execute as fast as it can.. which is not good and not required. instead you can write this logic in a separate thread and sleep the thread for say, 1 sec after every file content check... you can also try checking the variation in file size instead of checking content. — Jos, Jun 24 '16 at 05:12
Sorry, I don't understand redflar3, for I am new to Java. May you please elaborate a little more? I am intrigued. — Crazy Eddy, Jun 24 '16 at 05:26
Try this, or google about WatchService in java http://stackoverflow.com/questions/16251273/can-i-watch-for-single-file-change-with-watchservice-not-the-whole-directory — Doc, Jun 24 '16 at 05:28

score 0 · Accepted Answer · answered Jun 24 '16 at 05:18

you can check the time stamp of file to determine whether it has changed or not.

Sample code :

    Long fileLastModified;
    File file = new File("file");
    if (!file.exists()) {
        syserr
    }
    if (file.lastModified() <= this.fileLastModified) {
        return oldValue;
    }
    this.fileLastModified = file.lastModified();

Also, you should use threads as commented by redflar3

score 0 · Answer 2 · answered Jun 24 '16 at 05:22

Hi you can make a timer to check the file once every 2 seconds or so a snippet goes here

new java.util.Timer().schedule( 
    new java.util.TimerTask() {
        @Override
        public void run() {
            //Read your file
            if(fileEmpty){
               //Update your textfiled
               cancel(); //Stops this timer 
            }
        }
    }, 
    0,2000);

once your task is done just use purge(); to clear out all cancelled timers

hope this helps

How can I continously check to see if the text inside a text file has changed to empty? Java

2 Answers2