How to flushdns in java

Question

I am currently trying to find a way to flush my dns cache through a program in java. When I execute my code, the command prompt appears but i cant figure out how to get my code to execute.

import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;

class SyncPipe implements Runnable
{
public SyncPipe(InputStream istrm, OutputStream ostrm) {
  istrm_ = istrm;
  ostrm_ = ostrm;
 }
  public void run() {
  try
  {
      final byte[] buffer = new byte[1024];
      for (int length = 0; (length = istrm_.read(buffer)) != -1; )
      {
          ostrm_.write(buffer, 0, length);
      }
  }
  catch (Exception e)
  {
      e.printStackTrace();
  }
}

private final OutputStream ostrm_;
private final InputStream istrm_;
}
public class FlushCommand {

FlushCommand(InputStream errorStream, PrintStream err) {
    throw new UnsupportedOperationException("Not supported yet."); 
}

}

This is main method below:

    String command = "cmd /c start cmd.exe";
    {

};
Process p = null;
    try {// Execute command

Process child = Runtime.getRuntime().exec(command);

// Get output stream to write from it
OutputStream out = child.getOutputStream();

out.write("cd C:/ /r/n".getBytes());
out.flush();
out.write("dir /r/n".getBytes());
out.close();
        p = Runtime.getRuntime().exec(command);
    } catch (IOException ex) {
        Logger.getLogger(FlushDNS.class.getName()).log(Level.SEVERE, null, ex);
    }
new Thread((Runnable) new FlushCommand(p.getErrorStream(), System.err)).start();
new Thread((Runnable) new FlushCommnad(p.getInputStream(), System.out)).start();
PrintWriter stdin = new PrintWriter(p.getOutputStream());
stdin.println("dir c:\\ /A /Q");
stdin.println("ipconfig/flushdns");
// write any other commands you want here
stdin.close();
int returnCode = 0;
    try {
        returnCode = p.waitFor();
    } catch (InterruptedException ex) {
        Logger.getLogger(FlushDNS.class.getName()).log(Level.SEVERE, null, ex);
    }
System.out.println("Return code = " + returnCode);
}                                        

Answer 1

Why don't you start from very basic?

Your command is just opening a command window. If I remember correctly, the following should flush your dns and remain unclosed (cmd will not be automatically closed).

String command = "cmd.exe /c start cmd.exe /c start ipconfig /flushdns";
try{
      Runtime.getRuntime.exec(command);
catch(...){}

I have to check my old codes in my computer to make sure but I'd suggest you to start from basic and then do multi-threading etc.

Alternatively, you can use process builder to create your command.