To make the process appear concurrently in Swing java and Flush data to the GUI java

For this you need to us need to use SwingWorker Class which makes the data to be displayed in
Swing Frame as soon as the data is available.

class SwingWorkerDemo extends SwingWorker
//Integer- doInBackground return type and String - publish method Type
{
String command;

public SwingWorkerDemo(String cmd)
{
command=cmd;
area1.setEditable(false);

}
public Integer doInBackground() {
Runtime run = Runtime.getRuntime();
Process pr = null;
try {
pr = run.exec(command);
} catch (IOException ee) {
ee.printStackTrace();
}
int line;
try {
while ((line=pr.getInputStream().read())!=-1) {doInBackground
char c=(char)line;
// System.out.println(Character.toString(c));
publish(Character.toString(c));
}

while ((line=pr.getErrorStream().read())!=-1) {
char c=(char)line;
// System.out.println(Character.toString(c));
publish(Character.toString(c)); /// Publish to the process method to update GUI
}
}
catch (IOException error)
{
System.err.println("Oops");
}
return 0;
}
protected void process(java.util.List chunks) {
for ( String fd: chunks)
{
area1.append(fd); //GUI appending code

}
}
protected void done()
{
JOptionPane.showMessageDialog(null, "Find command Execution Completed.");
}

}

By making use of the SwingWorker class the GUI is updated in the Worker Thread .This makes it
possible for the data to be available in the GUI concurrently when read from the inputStream.

Here the doInBackground process runs the Complex Process and when we publish a data via publish method,the result can be made to be appended to the GUI by the process method.The code in the process methos is executed in the worker Thread so make sure to put the GUI updating code here.

The done method is executed once the process is completed.

Above code is liable to hanging as the process's getErrorStream and getOutputStream is executed in the same thread.So make sure you make the getErrorStream and getOutputStream to be executed in a separate Thread.

Process hangs in java

The correct solution according to my experience is the getErrorStream and getOutputStream
of the Process must be executed concurrently in a separate Thread

When you run a  Process proc

Runtime rt = Runtime.getRuntime();
Process proc = rt.exec(cmd);

You need to empty errorStream and outputStream in a separate Thread concurrently.
In case if you get the outputStream  first and get ErrorStream  afterwards it may lead to the Process hang or vice versa.

To make the  empty the errorStream and outputStream in a separate Thread you can use StreamGobbler as follows:

class StreamGobbler extends Thread
{
    InputStream is;
    String type;
    String command;
    StreamGobbler(InputStream is, String type)
   {
        this.is = is;
        this.type = type;
    }

   public void run()
      {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
           {
                 System.out.println(type + ">" + line);  //Stream to the STDOUT
            }{
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
               {
                System.out.println(type + ">" + line);
                area1.append(line);
              }
            } catch (IOException ioe)
              {
                ioe.printStackTrace();
               }
       }

     public static void main(String args[])
    {
                    Runtime rt = Runtime.getRuntime();
                    Process proc = rt.exec(command);
                    // error message
                    StreamGobbler errorGobbler = new
                        StreamGobbler(proc.getErrorStream(), "ERROR");          
                    //  output  message
                    StreamGobbler outputGobbler = new
                        StreamGobbler(proc.getInputStream(), "OUTPUT");

                    //Start the ErrorStream and inputStream in separate Threads
                    errorGobbler.start();
                    outputGobbler.start();

     }

ANd in case you are using a GUI for displaying the message you need to
use SwingWorker Thread .This i will cover in another blog.