javafx, socket programming, and threads - multithreading

Question

I am new to Java and JavaFX, so pardon my newbie questions. I have searched for the past couple of days for examples of what I am trying to do, but have been unable to find any answers.
Here is what I am trying to do: I am trying to create a simple javafx GUI client socket application using scene builder that will connect to a server and send/receive data. Simple enough, but when I try to implement this in Java FX, my GUI freezes. I have researched and found out that the reason is that the socket communications is taking all of the time, and the javafx GUI cannot update. My research has pointed me to using tasks. So, I have created a simple application that creates a task, connects to an internet socket (port 80), sends the command "GET / HTTP/1.1\r\n\r\n" which will request the page and then prints out each line received. The problem is that I want to do this over and over again (every 3 seconds). The task runs successfully once, but then it stops. In the following code, the lines that put the thread to sleep are never reached, but the lines that print any errors are not sent to system.out either.
Here is the controller code
package clientSocketExample;
import java.io.*;
import java.net.*;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.*;
import javafx.concurrent.Task;
/**
* Controller class of the HelloWorld sample.
*/
public class ClientSocketExampleController implements Initializable
{
#FXML
Button button;
private boolean keepRunning = true;
/**
* Initializes the controller class.
*/
#Override
public void initialize(URL url, ResourceBundle rsrcs)
{
if (button != null)
{
button.setOnAction(new EventHandler<ActionEvent>()
{
#Override
public void handle(ActionEvent event)
{
keepRunning = false;
System.out.println("Hello World\n");
}
});
}
// Create a background task to handle the Client-Server socket
// This is needed because JavaFX is not thread safe
Task<Integer> task = new Task<Integer>()
{
#Override
protected Integer call() throws Exception
{
Socket s = new Socket();
// String host = "www.google.com";
// String host = "www.amazon.com";
String host = "www.yahoo.com";
PrintWriter s_out = null;
BufferedReader s_in = null;
int lineNums = 0;
try
{
s.connect(new InetSocketAddress(host, 80));
System.out.println("Connected\n");
// Create writer for socket
s_out = new PrintWriter(s.getOutputStream(), true);
// Create reader for socket
s_in = new BufferedReader(new InputStreamReader(s.getInputStream()));
}
catch (IOException e)
{
// Host not found, so print error
System.err.println("Don't know about host : " + host);
System.exit(1);
}
// Loop forever waiting for task to be cancelled
while (isCancelled() == false)
{
// Send message to server
String message = "GET / HTTP/1.1\r\n\r\n";
s_out.println(message);
System.out.println("Message sent\n");
// Get response from server
try
{
String response;
while ((response = s_in.readLine()) != null)
{
System.out.print("Line #: "+lineNums+" ");
System.out.println(response);
lineNums++;
}
} catch (IOException e)
{
System.err.println("Couldn't get response from host");
}
System.out.println("Thread going to sleep\n\n\n");
Thread.sleep(3000);
System.out.println("Thread waking up from sleep\n\n\n");
} // End while
return lineNums;
}
}; // End Initialize
// start the background task
Thread th = new Thread(task);
th.setDaemon(true);
System.out.println("Starting background task...");
th.start();
}
}`
The Main.java class looks like this:
package clientSocketExample;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;
public class Main extends Application
{
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
Application.launch(Main.class, (java.lang.String[]) null);
}
#Override
public void start(Stage primaryStage)
{
try
{
AnchorPane page = (AnchorPane) FXMLLoader.load(Main.class
.getResource("ClientSocketExample.fxml"));
Scene scene = new Scene(page);
primaryStage.setScene(scene);
primaryStage.setTitle("Hello World Sample");
primaryStage.show();
} catch (Exception ex)
{
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
}`
And finally the FXML file looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.paint.*?>
<AnchorPane id="AnchorPane" prefHeight="365.0" prefWidth="378.0" xmlns:fx="http://javafx.com/fxml" fx:controller="clientSocketExample.ClientSocketExampleController">
<children>
<Button fx:id="button" layoutX="147.0" layoutY="28.0" text="Connect" />
<TitledPane animated="false" layoutY="159.0" prefWidth="378.0" text="Received Data">
<content>
<AnchorPane id="Content" minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0">
<children>
<TextArea fx:id="textAreaField" prefHeight="180.0" prefWidth="374.0" wrapText="true" />
</children>
</AnchorPane>
</content>
</TitledPane>
</children>
</AnchorPane>
Thanks in advance for your help
Wayne

Answer 1

The problem you are getting with the Gui that freezes is because its your "controller" class that connects to the socket. I had the same problem when i was creating my own chat program using JavaFx and JavaFx scene builder.
You can do two things:
Create a new class (SocketConnector()) that connects you to the socket.
Connect to the socket within your main class instead of controller
regardless you cannot connect to a socket within your controller class i am sorry that i am unable to describe details on why you cannot i just know that ive experianced this problem several times and this what the way to fix it!

Answer 2

A couple things need to change with your request:
Insert this into your request
"\r\nHost: <host>\r\nConnection: keep-alive"
This will make sure that the server doesn't close your connection after it responds to your request.
Change your while loop to this:
while (s_in.ready() && (response = s_in.readLine()) != null)
This will make sure there is something to read from the BufferedReader. Check these posts about why the BufferedReader will hang: https://stackoverflow.com/a/7855911/1359765 and https://stackoverflow.com/a/15510821/1359765