Connection conn = null;
        Statement ps = null;
        ResultSet rs = null;
        try{
            Class.forName("oracle.jdbc.driver.OracleDriver");//注册驱动
            //建立连接
            conn = DriverManager.getConnection("jdbc:oracle:thin:@10.148.73.67:1521:databaseName");
            //创建语句
            String sql = "select * from user";
            ps = conn.createStatement();
            //执行语句
            rs = ps.executeQuery(sql);
            //处理结果
            while(rs.next()) {
                System.out.println("userName:" + rs.getString("user_name"));
            }
        }catch(Exception e) {
            e.printStackTrace();
        }finally {
            //以下为释放连接
            try {
                if (rs != null)
                    try {
                        rs.close();
                    } catch (SQLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
            } finally {
                try {
                    if (ps != null)
                        try {
                            ps.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }

                } finally {

                    if (conn != null)
                        try {
                            conn.close();
                        } catch (SQLException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                }
            }
    
        }

------解决方案--------------------
楼主肯定没在项目中导入数据库驱动的JAR包！！！

------解决方案--------------------
没有导入驱动包

------解决方案--------------------