public static long getFreeDiskSpace(String dirName)
{
try
{
// guess correct 'dir' command by looking at the 
// operating system name
String os = System.getProperty("os.name");
String command;
if (os.equals("Windows NT") ||
os.equals("Windows 2000"))
{
command = "cmd.exe /c dir " + dirName;
}
else
{
command = "command.com /c dir " + dirName;
}
// run the dir command on the argument directory name
Runtime runtime = Runtime.getRuntime();
Process process = null;
process = runtime.exec(command);
if (process == null)
{
return - 1 ;
}
// read the output of the dir command
// only the last line is of interest 
BufferedReader in = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line;
String freeSpace = null;
while ((line = in.readLine()) != null)
{
freeSpace = line;
}
if (freeSpace == null)
{
return - 1 ;
}
process.destroy();
// remove dots & commas & leading and trailing whitespace
freeSpace = freeSpace.trim();
freeSpace = freeSpace.replaceAll("\\.", "");
freeSpace = freeSpace.replaceAll(",", "");
String[] items = freeSpace.split(" ");
// the first valid numeric value in items after(!) index  0 
// is probably the free disk space
int index =  1 ;
while (index < items.length)
{
try
{
long bytes = Long.parseLong(items[index++]);
return bytes;
}
catch (NumberFormatException nfe)
{
}
}
return - 1 ;
}
catch (Exception exception)
{
return - 1 ;
} 
}