private static StringBuilder sb4 = new StringBuilder();

  System.out.println("Waiting.");
        SocketChannel socketChannel
                = serverSocketChannel.accept();
        sb4.delete(0, sb4.length());

        System.out.println("Opened connection.");


          ByteBuffer b = ByteBuffer.allocate(9999);
System.out.println("Init");
        b = ByteBuffer.allocate(9999);
        b.clear();
        b.put("K".toString().getBytes());
        b.flip();
        while (b.hasRemaining()) {
          socketChannel.write(b);
        }

      Boolean taken = false;
        StringBuilder msg = new StringBuilder();
        String tmp;
        int cnt = 0;
        b.clear();
        cnt = socketChannel.read(b);
        while (cnt > 0) {
          b.flip();
          tmp = new String(b.array()).substring(0, cnt);
          msg.append(tmp);
          b.clear();
          if (msg.toString().endsWith("]"))
            break;
          cnt = socketChannel.read(b);
        }


        System.out.println("New message got [ " + msg + " ] ");
        String[] array=msg.toString().split("§");
         String url = "jdbc:mysql://localhost:3306/chat";
        String name = "root";
        String pass = "1111";
        try {
            Connection con = DriverManager.getConnection(url, name, pass);

            Statement s = con.createStatement();
            ResultSet r = s.executeQuery("select * from user");
            while (r.next()) {

            String username = r.getString("name");





                System.out.println(username);
                if(array[0].equals(username)) {
                taken=true;


                }
            }
        } catch (SQLException ex) {
        }
          System.out.println(taken);
    if(taken) {
    sb4.delete(0, sb4.length());
sb4.append("F");
    }
    else {

                    Connection con;
            try {
                con = DriverManager.getConnection(url, name, pass);
                        Statement statement = con.createStatement();
statement.executeUpdate("INSERT INTO user " + "VALUES ('"+array[0]+"','"+array[1]+"')");


            } catch (SQLException ex) {
                Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
            }



    sb4.delete(0, sb4.length());
sb4.append("O");
    }
        System.out.println("Returning result");
        b = ByteBuffer.allocate(9999);
        b.clear();
        b.put(sb4.toString().getBytes());
        b.flip();
        while (b.hasRemaining()) {
          socketChannel.write(b);
        }

        System.out.println("Done, waiting for next one.");



      } catch (IOException ex) {
        System.out.println("Failed to communicate. " + ex.getMessage());
      }
    }