Redirect output from stderr, stdout to a JTextArea

[Konstantinos Vasileiou]

I have implemented a program that invokes some Linux commands to complete a number of tasks. My problem is that I want to add a GUI to the application, so I need to somehow redirect the output of the commands from the error and the out streams to a graphical components, such as a JTextArea.... However, I am not sure how to do it. The code I currently have looks like this:

 
Process process = Runtime.getRuntime().exec(commandString);
InputStream stderr = process.getErrorStream();
InputStreamReader isr = new InputStreamReader(stderr);
BufferedReader br = new BufferedReader(isr);
String line = null;
System.out.println("<OUTPUT>");
while ((line = br.readLine()) != null)
        System.out.println(line);
System.out.println("</OUTPUT>");
exitVal = process.waitFor();   

[Rob Camick]

The [Message Console might be what you are looking for.

[Ramses Butarbutar]

Hi Konstantinos ,

If i'm not mistaken, you wanna get your error (your stack trace info???) and put in some components such a JTextArea ?

Just define the exception, catch it, put it in stringwriter and parse into string.
After that you can easily throw it into your JTextArea.

   
Exception ex = new Exception("something went wrong");
StringWriter sw = new StringWriter();
ex.printStackTrace(new PrintWriter(sw));
String stacktrace = sw.toString();
System.out.println("stacktrace = " + stacktrace);

Have a nice try..

[Rob Spoor]

Rob Camick wrote:The [Message Console might be what you are looking for.

It would be great if it was the stderr and stdout of the current application that should be great. In this case, it's the stderr and stdout from a separate process.

Konstantinos, first of all, please read this. You'll find it very useful.
In that article, the StreamGobbler code on page 4 is almost what you want. However, instead of printing, you want to add it:

class StreamGobbler extends Thread
{
    private final InputStream is;
    private final JTextArea text;

    public StreamGobbler(InputStream is, JTextArea text)
    {
        this.is = is;
        this.text = text;
    }

    public void run()
    {
        try
        {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
            {
                text.append(line + "\n"); // JTextArea.append is thread safe
            }
        }
        catch (IOException ioe)
        {
            text.append(ioe.toString()); // note below
            ioe.printStackTrace();  
        }
    }
}

Apart from appending only the exception's String form, you can print the stack trace to the text area as well, using my patented ( ) TextAreaWriter:

public class TextAreaWriter extends Writer
{
    protected final JTextArea text;

    public TextAreaWriter(JTextArea text)
    {
        if (text == null)
        {
            throw new NullPointerException();
        }
        this.text = text;
    }

    @Override
    public void write(char[] c, int off, int len)
    {
        text.append(new String(c, off, len));
    }

    @Override
    public void flush()
    {
        // does nothing
    }

    @Override
    public void close()
    {
        // does nothing
    }
}

ioe.printStackTrace(new PrintWriter(new TextAreaWriter(text));

[Konstantinos Vasileiou]

Thank you - very helpful and detailed reply!