public String MD5( String str )
{
    MessageDigest md;
    try
    {
        md = MessageDigest.getInstance( "MD5" );
        md.reset();
        md.update( str.getBytes( "UTF-8" ) );
        byte[] digest = md.digest();

        BigInteger bigInt = new BigInteger( 1, digest );
        String hashtext = bigInt.toString( 16 );

        return hashtext;
    } catch ( Exception e )
    {
        return null;
    }
}