连接数据库的类

    /**
    * 构造数据库的连接和访问类
    */
    public Mysql() throws Exception {
        Class.forName(CONST.dbdriver);
        conn = DriverManager.getConnection(CONST.dburl);
        stmt = conn.createStatement();
    }
    public Mysql(String sql) throws Exception {
        Class.forName(CONST.dbdriver);
        conn = DriverManager.getConnection(CONST.dburl);
        this.prepareStatement(sql);
    }

    /**
    * PreparedStatement
    * @return sql 预设SQL语句
    */
    public void prepareStatement(String sql) throws SQLException {
        prepstmt = conn.prepareStatement(sql);
    }

    public Connection getConn() { return this.conn; }
    public Statement getStmt() { return this.stmt; }
    public PreparedStatement getPrepstmt() { return this.prepstmt; }
   
    /**
    * 执行SQL语句返回字段集
    * @param sql SQL语句
    * @return ResultSet 字段集
    */
    public ResultSet executeQuery(String sql) throws SQLException {
        if (stmt != null) {
            return stmt.executeQuery(sql);
        } else return null;
    }

    public ResultSet executeQuery() throws SQLException {
        if (prepstmt != null) {
            return prepstmt.executeQuery();
        } else return null;
    }
   
    /**
    * 执行SQL语句
    * @param sql SQL语句
    */
    public void executeUpdate(String sql) throws SQLException {
        if (stmt != null)
            stmt.executeUpdate(sql);
    }

    public void executeUpdate() throws SQLException {
        if (prepstmt != null)
            prepstmt.executeUpdate();
    }

    /**
    * 关闭连接
    */
    public void close() throws Exception {
        if (stmt != null) {
            stmt.close();