jdbc access java part

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;
import java.util.List;
import java.util.ArrayList;
import java.sql.ResultSetMetaData;

public class DevJDBC {

    static Connection conn;
    static PreparedStatement stmt;
    static ResultSet result;
    static Map<Integer, String> items= new HashMap<Integer,String>() ;
    static Map<String, Double> values = new HashMap<String, Double>();
    static List<PreparedStatement> stmtlist = new ArrayList<PreparedStatement>();
    //static List<HashMap<Integer, String>> itemlist = new ArrayList<HashMap<Integer,String>>();

    public static boolean getConnection(String url, String user, String password) {

        try {

            //Class.forName("oracle.jdbc.driver.OracleDriver");
            System.out.println("connecting the database...");
            conn = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
        }

        if (conn != null) {
            System.out.println("connect the database success");
            return true;

        } else {
            return false;
        }
    }
    public static boolean execute(String sql) {

        try {
            //System.out.println("execute sql "+sql);
            Statement stat = conn.createStatement();
            stat.execute(sql);
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    public static int prepareStmt(String sql) {
        int index = 0 ;
        try {
            // System.out.println(sql);
            stmt = conn.prepareStatement(sql);
            stmtlist.add(stmt);
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (stmt != null) {
            System.out.println(sql);
            index = stmtlist.size();
            System.out.println("prepare sql stmt count:" + index);
            return index;
        } else {

            return 0;

        }

    }

    public static boolean executeQuery(int index) {
        // Tag_data Tag = new Tag_data();
        try {
            if (stmt != null) {
                System.out.println("index of stmt:" + (index-1));
                PreparedStatement execstmt = stmtlist.get(index-1);
                result = execstmt.executeQuery();
            }
        } catch (Exception e) {

            e.printStackTrace();
        }
        if (result != null) {
            System.out.println("execute query success");
            return true;
        } else {
            System.out.println("execute query failed");
            return false;
        }
    }

    public static void setColname(int index, String colname) {

        items.put(index, colname);
        System.out.println(items);
        //itemlist.add(items);
        //System.out.println(itemlist);
    }

    public static double readValue(int i ) {
        double value = 0;
        int j;
        try {
            ResultSetMetaData rsmd = result.getMetaData();
            if (items.containsKey( i )) {
                String colname = items.get(i);
                String colname1 = colname.toUpperCase();
                while (result.next()) {
                    for (j = 1; j < rsmd.getColumnCount() + 1; j++)
                    {
                        // System.out.println("put the value start..");
                        // value[j] = result.getDouble(j);
                        values.put(rsmd.getColumnName(j), result.getDouble(j));
                        System.out.println("database value: " + " columnname:" + rsmd.getColumnName(j) + " value:"
                                + result.getDouble(j));
                    }
                }
                if (values.containsKey(colname1)) {
                    value = values.get(colname1);
                    System.out.println(" read  tag value:" + " columnname:" + colname1 + "  tag value:" + value);
                }
            }
        } catch (Exception e) {

            e.printStackTrace();
        }
        return value;
    }

    public static void logoff() throws SQLException {

        if (result != null)
            result.close();
        if (stmtlist != null)
            {     for(PreparedStatement stmt:stmtlist ){
                    stmt.close();
                }
            }
        if (conn != null)
            conn.close();
        items.clear();
        values.clear();
        stmtlist.clear();
        //itemlist.clear();
        System.out.println("database closed!");

    }

}