jdbc连接oracle数据库问题

   下面是JDBC连接oracle数据库流程：
        String dbURL = "jdbc:oracle:thin:@url:1521:service_name";
        String userName = "数据库名";
        String userPwd = "密码";
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;    

        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con = DriverManager.getConnection(dbURL, userName, userPwd);
            System.out.println("加载数据库驱动成功！");
            System.out.println("数据库连接成功！");
            st = con.createStatement();

            String sql = "select * from ETL.BD_PSNDOC";//数据库表名前面尽量加上数据库名字

            rs = st.executeQuery(sql);
            while (rs.next()) {
              .......................
             }
        }catch(Exception e){
            e.printStackTrace();
        }
        try {
            if(rs!=null){
                rs.close();
            }
            if (st != null) {
                st.close();
            }
            if (con != null) {
                con.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }