Why am I getting an Resultset already closed error?

 public class Server implements Runnable {
        private static int port = 1600, maxConnections = 0;
        public static Connection connnew = null;
        public static Connection connnew1 = null;
        public static Statement stnew, stnew1, stnew2, stnew3, stnew4;

        public void getConnection() {
            try {
                Class.forName("org.gjt.mm.mysql.Driver");
                connnew = DriverManager.getConnection("jdbc:mysql://localhost/db_alldata", "root", "flashkit");
                connnew1 = DriverManager.getConnection("jdbc:mysql://localhost/db_main", "root", "flashkit");
                stnew = connnew.createStatement();
                stnew1 = connnew.createStatement();
                stnew2 = connnew1.createStatement();
                stnew3 = connnew1.createStatement();
                stnew4 = connnew1.createStatement();
            } catch (Exception e) {
                System.out.print("Get Connection Exception---"
                    + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "----- > " + e);
            }

        }

        public void closeConnection() {
            try {
                if (!(connnew.isClosed())) {
                    stnew.close();
                    stnew1.close();
                    connnew.close();
                }
                if (!(connnew1.isClosed())) {
                    stnew2.close();
                    stnew3.close();
                    stnew4.close();
                    connnew1.close();
                }

            } catch (Exception e) {
                System.out.print("Close Connection Closing Exception-----"
                    + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "------->" + e);
            }
        }

        Server() {
            try {

            } catch (Exception ee) {
                System.out.print("Server Exceptions in main connection--"
                    + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "------>" + ee);
            }

        }

        public static void main(String[] args) throws SQLException {
            int i = 0;
            Server STUD = new Server();
            STUD.getConnection();

            try {
                ServerSocket listener = new ServerSocket(port);
                Socket server;
                while ((i++ < maxConnections) || (maxConnections == 0)) {

                    @SuppressWarnings("unused")
                    doComms connection;
                    server = listener.accept();
                    try {
                        ResultSet checkconnection = stnew4
                            .executeQuery("select count(*) from t_studentdetails");
                        if (checkconnection.next()) {
                            // DO NOTHING IF EXCEPTION THEN CLOSE ALL CONNECTIONS AND OPEN NEW
                            // CONNECTIONS
                        }

                    } catch (Exception e) {
                        System.out.print("Db Connection Lost Closing And Re-Opning It--------"
                            + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())
                            + "--------" + e);
                        STUD.closeConnection();
                        STUD.getConnection();
                    }
                    doComms conn_c = new doComms(server, stnew, stnew1, stnew2, stnew3);
                    Thread t = new Thread(conn_c);
                    t.start();
                }
            } catch (IOException ioe) {
                System.out.println("Main IOException on socket listen: " + ioe);

            }

        }

        public void run() {

        }
    }

    class doComms implements Runnable {
        private Socket server;
        private String input;
        static Connection conn = null;
        static Connection conn1 = null;
        static Statement st, st1, st2, st3;

        doComms(Socket server, Statement st, Statement st1, Statement st2, Statement st3) {
            this.server = server;
            doComms.st = st;
            doComms.st1 = st1;
            doComms.st2 = st2;
            doComms.st3 = st3;
        }

        @SuppressWarnings("deprecation")
        public void run() {
            input = "";
            // char ch;
            try {
                DataInputStream in = new DataInputStream(server.getInputStream());
                OutputStreamWriter outgoing = new OutputStreamWriter(server.getOutputStream());
                while (!(null == (input = in.readLine()))) {

                    savetodatabase(input, server.getPort(), outgoing);

                }

            } catch (IOException ioe) {
                System.out.println("RUN IOException on socket listen:-------"
                    + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "----- " + ioe);
                ioe.printStackTrace();
            }

        }

        public void savetodatabase(String line, int port1, OutputStreamWriter outgoing) {
            try {
                String Rollno = "-", name = "-", div = "-", storeddate = "-", storedtime = "-", mailfrom = "";
                String newline = line;
                String unitid = "-";

                storeddate = new SimpleDateFormat("yyyy-MM-dd").format(new java.util.Date());
                storedtime = new SimpleDateFormat("HH:mm:ss").format(new java.util.Date());
                String sql2 = "delete from t_currentport where PortNumber='" + port1 + "''";
                st2.executeUpdate(sql2);
                sql2 = "insert into t_currentport (unitid, portnumber,thedate,thetime) values >('"
                    + unitid + "','" + port1 + "','" + storeddate + "','" + storedtime + "')";
                st2.executeUpdate(sql2);
                String tablename = GetTable();
                String sql = "select * from t_studentdetails where Unitid='" + unitid + "'";
                ResultSet rst = st2.executeQuery(sql);
                if (rst.next()) {
                    Rollno = rst.getString("Rollno");
                    name = rst.getString("name");
                    div = rst.getString("div");
                }
                String sql1 = "insert into studentInfo StoredDate,StoredTime,Subject,UnitId,Body,Status,Rollno,div,VehId,MailDate,MailTime,MailFrom,MailTo,Header,UnProcessedStamps) values('"
                    + storeddate + "','" + storedtime + "','" + unitid + "','" + unitid + "','" + newline
                    + "','Pending','" + Rollno + "','" + div + "','" + name + "','" + storeddate
                    + "','" + storedtime + "','" + mailfrom + "','" + mailfrom + "','-','-')";
                st1.executeUpdate(sql1);
            } catch (Exception e) {
                System.out.print("Save to db Connection Exception--"
                    + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "-->" + e);

            }
        }

    }