spring boot mybatis如何捕获连接数据库失败的异常？

问题描述：

使用mybatis查询数据时，想捕获数据库连接失败的异常。

以下是想通过NetException来捕获数据库连接失败的异常，但是报错。

请问该怎么处理，才能准确的捕获到连接失败的异常？

        try {
            int userId = 1;
            User user = userMapper.findById(userId);
        } catch (NetException e) {
            // TODO: handle exception
            logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
            System.out.println(e.getStackTrace());
            logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
        }

public interface UserMapper {
    @Select("SELECT * FROM SYSTEM_USER WHERE id=#{id}")
    @Results({ @Result(property = "credentialsSalt", column = "credentials_salt"),
            @Result(property = "createTime", column = "create_time") })
    User findById(int id);

    @Select("SELECT * FROM user WHERE username=#{username}")
    @Results({ @Result(property = "credentialsSalt", column = "credentials_salt"),
            @Result(property = "createTime", column = "create_time") })
    User queryByUsername(String username);
}

第 1 个答案：

        try {
            int userId = 1;
            User user = userMapper.findById(userId);
        } catch (Exception e) {
            if (e instanceof NetException) {
                // TODO: handle exception
                logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
                System.out.println(e.getStackTrace());
                logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
            } else {
                // TODO: handle exception
                logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
                System.out.println(e.getStackTrace());
                logger.info("xxxxxxxxxxxxxxxxxxxxxxx");
            }
        }

仅供参考。

一个网上听课系统，每隔一段时间需要答题，然后才能继续听（如图）。想问如何实现自动点击这个“提交”按钮？JS可以实现吗？还是只能模拟点击？