how to post the result of a running thread to a JtextArea (Java)

mia_tech · 07-08-2012, 06:30 PM

guys, I have a GUI that scan a range of ip address when press "scan" button; however, I'm having trouble displaying the result in the textArea box. I'm using a threads for my execution. here's the action performed when press the scan button. How could I get the output of the scan and put it into a textArea.setText(...);

Code:

IPrange netRange = new IPrange();
ArrayList<String> r = netRange.getRange();

public void StartIPscan() {
        String ipFrom = ipTextFrom.getText();
        String ipTo = ipTextTo.getText();
        netRange.setFromip(ipFrom);
        netRange.setToip(ipTo);
        netRange.StrToIP();
        netRange.calcNetwork();
        /**
         * ping sweep network
         */
        Runnable scan = new IPscanner(r);
        Thread t = new Thread(scan);
        t.start();
 
    }

here's the IPrange class that implements Runnable interface

Code:

import java.io.*;
import java.net.*;
import java.util.*;
public class IPscanner implements Runnable{
    private String ipadd = "";
    ArrayList<String> block;
    public IPscanner(ArrayList r)
    {
        block = r;
    }
    public void run(){
            boolean ping = false;
            //ipadd = block.size()+"";
            ipadd = "Scanning network "+"\""+block.get(0)+"...\""+"\n";
 
            for(int i = 0; i < block.size(); i++)
            {
                try
                {
                    int timeout = 1000;
                    InetAddress address = InetAddress.getByName(block.get(i));
                    //scanProgressBar.setValue(i);//updating progress bar
                    ping = address.isReachable(timeout);
                    if(ping == true)
                    {
                         ipadd += block.get(i)+" ---> is alive!"+"\n";
                    }
                    else
                    {
                        ipadd += block.get(i)+"\n";
                    }
                }
                catch(IOException e)
                {
                    System.out.println(e);
                }
           }
 
        }
    public void setIPadd(String s)
    {
        ipadd = s;
    }
    public String getIPadd()
    {
        return ipadd;
    }
}

dwhitney67 · 07-08-2012, 07:56 PM

Quote:

Originally Posted by mia_tech

guys, I have a GUI that scan a range of ip address when press "scan" button; however, I'm having trouble displaying the result in the textArea box. I'm using a threads for my execution. here's the action performed when press the scan button. How could I get the output of the scan and put it into a textArea.setText(...);

I see nothing in your code demonstrating how you are attempting to set the text. Did you forget to post the relevant code?

Is it your desire to post the results of all scans once the task is complete, or did you want to post intermediate results (sort of like a progress of completed pings)??

Here's a simple example demonstrating the use of JTextArea:

Code:

import javax.swing.*;

public class DisplayText extends JFrame
{
    private JTextArea textArea = new JTextArea();

    public DisplayText()
    {
        super("My Text Displayer");

        add(textArea);

        setSize(300, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void display()
    {
        setVisible(true);
    }

    public void showText(String text)
    {
        textArea.setText(text);
    }

    public static void main(String[] args)
    {
        DisplayText dt = new DisplayText();
        dt.display();

        String text = "";

        for (int i = 0; i < 10; ++i)
        {
            text += i+1 + "\n";

            dt.showText(text);

            try { Thread.sleep(1000); } catch (InterruptedException e) {}
        }
    }
}

mia_tech · 07-09-2012, 11:49 AM

Quote:

Originally Posted by dwhitney67

I see nothing in your code demonstrating how you are attempting to set the text. Did you forget to post the relevant code?

that is the problem... posting something to textArea is not difficult you get the return of your method and post it.... my problem is that I'm doing the scan implementing the run() method which is void(does not return anything). And the result is stored in "ipadd" and I have no way to access it.

Quote:

Is it your desire to post the results of all scans once the task is complete, or did you want to post intermediate results (sort of like a progress of completed pings)??

well, ideally it would be better to display as the scan is in progress, otherwise you would be sitting there wondering what's happening while the scan is in progress.

dwhitney67 · 07-09-2012, 11:57 AM

You would need to pass the handle to the JFrame object to IPScanner, so that IPScanner can, while is is performing the thread, update the JText area.

Here's an incomplete example:

Code:

public IPScanner implements Runnable
{
    private String ipadd = "";
    ArrayList<String> block;
    MyFrame frame;

    public IPscanner(ArrayList<String> r, MyFrame frame)
    {
        this.block = r;
        this.frame = frame;
    }

    public void run()
    {
            boolean ping = false;
            //ipadd = block.size()+"";
            ipadd = "Scanning network "+"\""+block.get(0)+"...\""+"\n";
 
            for(int i = 0; i < block.size(); i++)
            {
                try
                {
                    int timeout = 1000;
                    InetAddress address = InetAddress.getByName(block.get(i));
                    //scanProgressBar.setValue(i);//updating progress bar
                    ping = address.isReachable(timeout);
                    if(ping == true)
                    {
                         ipadd += block.get(i)+" ---> is alive!"+"\n";
                    }
                    else
                    {
                        ipadd += block.get(i)+"\n";
                    }

                    
                    // Update the frame with the ping status
                    frame.updateText(ipadd);
                    
                }
                catch(IOException e)
                {
                    System.out.println(e);
                }
           }
 
        }
}

P.S. I see no reason for ipadd to be declared as a class member; it really only needs to be used locally within run().

P.S. #2 Make sure that the JTextArea, when updated within MyFrame's updateText() [or whatever you call it] is done in a thread-safe manner. For example:

Code:

public void updateText(final String text)
{
    SwingUtilities.invokeLater(new Runnable()
    {
        @Override
        public void run()
        {
            myTextArea.setText(text);
        }
    });
}

mia_tech · 07-12-2012, 12:13 PM

Quote:

Originally Posted by dwhitney67

You would need to pass the handle to the JFrame object to IPScanner, so that IPScanner can, while is is performing the thread, update the JText area.

Here's an incomplete example:

Code:

public IPScanner implements Runnable
{
    private String ipadd = "";
    ArrayList<String> block;
    MyFrame frame;

    public IPscanner(ArrayList<String> r, MyFrame frame)
    {
        this.block = r;
        this.frame = frame;
    }

    public void run()
    {
            boolean ping = false;
            //ipadd = block.size()+"";
            ipadd = "Scanning network "+"\""+block.get(0)+"...\""+"\n";
 
            for(int i = 0; i < block.size(); i++)
            {
                try
                {
                    int timeout = 1000;
                    InetAddress address = InetAddress.getByName(block.get(i));
                    //scanProgressBar.setValue(i);//updating progress bar
                    ping = address.isReachable(timeout);
                    if(ping == true)
                    {
                         ipadd += block.get(i)+" ---> is alive!"+"\n";
                    }
                    else
                    {
                        ipadd += block.get(i)+"\n";
                    }

                    
                    // Update the frame with the ping status
                    frame.updateText(ipadd);
                    
                }
                catch(IOException e)
                {
                    System.out.println(e);
                }
           }
 
        }
}

when you mean a handle to a jframe you mean passing JTextArea as variable to the IPScanner class, then updating it from there? or a jFrame is different from JtextArea?

Quote:

P.S. I see no reason for ipadd to be declared as a class member; it really only needs to be used locally within run().

I agree!..

Quote:

P.S. #2 Make sure that the JTextArea, when updated within MyFrame's updateText() [or whatever you call it] is done in a thread-safe manner. For example:

Code:

public void updateText(final String text)
{
    SwingUtilities.invokeLater(new Runnable()
    {
        @Override
        public void run()
        {
            myTextArea.setText(text);
        }
    });
}

this method would be part of my IPScanner class right?

Thanks

dwhitney67 · 07-12-2012, 01:25 PM

Quote:

Originally Posted by mia_tech

when you mean a handle to a jframe you mean passing JTextArea as variable to the IPScanner class, then updating it from there? or a jFrame is different from JtextArea?

I would not pass the JTextArea object; keep that tucked away in your JFrame class. By reducing the exposure of the contents of a class, you will adhere to the notions of encapsulation. Your IPScanner should merely tell the JFrame object what text to display. If tomorrow, you decide to change the JTextArea to some other "widget", you would not need to change the IPScanner code.

I hope my response above answers your second question (hint: the updateText() method should be implemented within your JFrame class).

mia_tech · 07-12-2012, 04:03 PM

Quote:

Originally Posted by dwhitney67

I would not pass the JTextArea object; keep that tucked away in your JFrame class. By reducing the exposure of the contents of a class, you will adhere to the notions of encapsulation. Your IPScanner should merely tell the JFrame object what text to display. If tomorrow, you decide to change the JTextArea to some other "widget", you would not need to change the IPScanner code.

I hope my response above answers your second question (hint: the updateText() method should be implemented within your JFrame class).

Ok, I think I got what you meant. Instead of passing the JTextArea(which I tried with same results) I created an Object of my JFrame and pass it with the constructor of IPScanner class; however, now I'm getting a runtime error

Code:

Exception in thread "Thread-2" java.lang.NullPointerException
	at lanscan.IPscanner.run(IPscanner.java:49)
	at java.lang.Thread.run(Thread.java:722)

and line 49 of IPScanner contains

Code:

myFrame.updateText(ipadd);

here's my code after I made the mods you suggested... thanks for the help

portions of my LanScanFrame class (JFrame)

Code:

IPrange netRange = new IPrange();
    ArrayList<String> r = netRange.getRange(); 
    LanScanFrame frame;
    
    
    //performing ip scan
     public void StartIPscan() {
        String ipFrom = ipTextFrom.getText();
        String ipTo = ipTextTo.getText();
        netRange.setFromip(ipFrom);
        netRange.setToip(ipTo);
        netRange.StrToIP();
        netRange.calcNetwork();
        
        //ping sweep network         
        //Runnable scan = new IPscanner(r);
        Thread t = new Thread(new IPscanner(r, frame));
        t.start();       
        
    }
     
    public void updateText(final String text)
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                ipOutputText.setText(text);
            }
        });
    }
    
    //clear ip range and ip output text area
    public void clearIPrange()
    {
        ipTextFrom.setText("");
        ipTextTo.setText("");
        ipOutputText.setText("");
        
        
    }

IPScanner class

Code:

import java.io.IOException;
import java.net.InetAddress;
import java.util.ArrayList;
public class IPscanner implements Runnable{
    
    ArrayList<String> block;
    LanScanFrame myFrame;
    
    
    public IPscanner(ArrayList<String> r, LanScanFrame f)
    {
        block = r;
        myFrame = f;
    }
    
    public void run(){
            String ipadd = "";
            boolean ping = false;
            //ipadd = block.size()+"";
            ipadd = "Scanning network "+"\""+block.get(0)+"...\""+"\n";

            for(int i = 0; i < block.size(); i++)
            {
                try
                {
                    int timeout = 1500;
                    InetAddress address = InetAddress.getByName(block.get(i));
                    //scanProgressBar.setValue(i);//updating progress bar
                    ping = address.isReachable(timeout);
                    if(ping == true)
                    {
                         ipadd += block.get(i)+" ---> is alive!"+"\n";
                    }
                    else
                    {
                        ipadd += block.get(i)+"\n";
                    }
                    myFrame.updateText(ipadd);
                }
                catch(IOException e)
                {
                    System.out.println(e.getMessage());
                }
           }           
        }
}

dwhitney67 · 07-12-2012, 04:51 PM

I do not see within your StartIPscan class where you are instantiating a LanScanFrame object. I see where you have declared the object (variable name is 'frame'), but no where is there a "new LanScanFrame()" statement. This may explain why 'frame' is null.

Btw, LanScanFrame should be defined to be something like the following; I notice that you have updateText() in StartIPscan... that's wrong:

Code:

public class LanScanFrame extends JFrame
{
    ...

    public void updateText(final String text)
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                ipOutputText.setText(text);
            }
        });
    }
}

mia_tech · 07-13-2012, 11:32 AM

Quote:

Originally Posted by dwhitney67

I do not see within your StartIPscan class where you are instantiating a LanScanFrame object. I see where you have declared the object (variable name is 'frame'), but no where is there a "new LanScanFrame()" statement. This may explain why 'frame' is null.

Btw, LanScanFrame should be defined to be something like the following; I notice that you have updateText() in StartIPscan... that's wrong:

Code:

public class LanScanFrame extends JFrame
{
    ...

    public void updateText(final String text)
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                ipOutputText.setText(text);
            }
        });
    }
}

startIpscan is a method not a class... startIpscan and updateText are part of my LanScanFrame. I made some modification like constructing frame object in IPscanner class. take a look and see if it's correct

Code:

IPrange netRange = new IPrange();
    ArrayList<String> r = netRange.getRange(); 
    LanScanFrame frame;
    
    
    //performing ip scan
     public void StartIPscan() {
        String ipFrom = ipTextFrom.getText();
        String ipTo = ipTextTo.getText();
        netRange.setFromip(ipFrom);
        netRange.setToip(ipTo);
        netRange.StrToIP();
        netRange.calcNetwork();
        
        //ping sweep network         
        //Runnable scan = new IPscanner(r);
        Thread t = new Thread(new IPscanner(r, frame));
        t.start();         
    }

public void updateText(final String text)
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                ipOutputText.setText(text);
            }
        });
    }

IPscanner class

Code:

import java.io.IOException;
import java.net.InetAddress;
import java.util.ArrayList;
import javax.swing.JTextArea;
public class IPscanner implements Runnable{
    
    ArrayList<String> block;
    LanScanFrame myFrame = new LanScanFrame();
       
    public IPscanner(ArrayList r, LanScanFrame t)
    {
        block = r;
        myFrame = t;
    }
    
    public void run(){
        
        String ipadd;            
        boolean ping;
        //ipadd = block.size()+"";
        ipadd = "Scanning network "+"\""+block.get(0)+"...\""+"\n";

        for(int i = 0; i < block.size(); i++)
        {
            try
            {
                int timeout = 2000;
                InetAddress address = InetAddress.getByName(block.get(i));
                //scanProgressBar.setValue(i);//updating progress bar
                ping = address.isReachable(timeout);
                if(ping == true)
                {
                        ipadd += block.get(i)+" ---> is alive!"+"\n";
                }
                else
                {
                    ipadd += block.get(i)+"\n";
                }
                
                
            }
            catch(IOException e)
            {
                System.out.println(e.getMessage());
            }
        } 
           
         myFrame.updateText(ipadd);   
            
    }
    
    
}

by the way when I start the scan I'm getting exceptions

Code:

Exception in thread "Thread-2" java.lang.NullPointerException
	at lanscan.IPscanner.run(IPscanner.java:59)
	at java.lang.Thread.run(Thread.java:722)

dwhitney67 · 07-13-2012, 11:44 AM

Quote:

Originally Posted by mia_tech

startIpscan is a method not a class... startIpscan and updateText are part of my LanScanFrame.

This would have been obvious had you posted all of your code; not just snip of it.

So, why do you declare a LanScanFrame object, 'frame', within the LanScanFrame class??

Quote:

Originally Posted by mia_tech

by the way when I start the scan I'm getting exceptions

Code:

Exception in thread "Thread-2" java.lang.NullPointerException
	at lanscan.IPscanner.run(IPscanner.java:59)
	at java.lang.Thread.run(Thread.java:722)

That is because you are still passing a null object to your thread. Now that you have revealed that LanScanFrame is the JFrame class that starts the thread, try something like:

Code:

public LanScanFrame extends JFrame
{
    ...

    public void StartIPscan() {
        ...

        Thread t = new Thread(new IPscanner(r, this));
        t.start();         
    }

    ...
}