Checking for a valid file name

Hi All

I am writing a swing application.

users should enter filename (should be .txt) as input in a textbox,
they should enter absolute path.

I need to check if the file name entered is a valid , before creating
the file.

if the user enters c:\mydir\sample.txt.
- I need to make sure that c:\mydirs is a vaild directory and I have
write permissions to write in the directory
-That user entered .a valid text file (ending with .txt in the file
name)
- handle conditions like empty string in file name
- make sure they entered full path instead of just file name.
-make sure they used proper file separator
etc

Is there a better way to do this..

When I am coding for this..
I am writing it like a series of if - then -else statements

if( StringUtils.isEmpty(destnFile) == true)
         {
         JOptionPane.showMessageDialog(this, "Please enter a valid
file name");
         return;
         }
         if( destnFile.endsWith(".txt") == false)
         {
         JOptionPane.showMessageDialog(this, "Converted file should
be an text file (.txt)");
         return;
         }

         String scriptDir =
destnFile.substring(0,destnFile.lastIndexOf(File.pathSeparator));
         File scriptDirLoc = new File(scriptDir);
         if( scriptDirLoc.isDirectory() == false)
          {
          JOptionPane.showMessageDialog(this, scriptDir+": is not a
valid directory");
          return;
          }

Please let me know.