ASP.Net C# - try-catch-finally和using语句

Question

因此，我已经习惯了使用try-catch-finally语句进行编码，而不包括using语句，我正在尝试将后者合并到我的代码中。

我已经附上了我的原始和修改后的代码如下。这个修改足够了吗？

此外，关于捕获错误，我已经在这里看到了以下代码多次使用。什么时候应该使用/不使用它，因为它不会通知用户错误？

catch (Exception ex)
{
    throw ex;
}

原始代码：

protected void signIn()
{
    string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
    MySqlConnection conn = new MySqlConnection(connStr);

    MySqlCommand comm;
    comm = new MySqlCommand("Select user_id, username, email, salt, hashed_pw, role, activated FROM users WHERE username=@username", conn);
    comm.Parameters.Add("@username", MySqlDbType.VarChar);
    comm.Parameters["@username"].Value = txtUsername.Text;
    MySqlDataReader reader;

    try
    {
        conn.Open();
        reader = comm.ExecuteReader();

        if (reader.Read())
        {
            string saltAndPwd = String.Concat(txtPassword.Text, reader["salt"].ToString());
            string hashSaltAndPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");

            if (hashSaltAndPwd.Equals(reader["hashed_pw"].ToString()))
            {
                if (reader["activated"].ToString().Equals("Y"))
                {
                    Session["Username"] = reader["username"].ToString();
                    Session["Role"] = reader["role"].ToString();
                    Session["UserID"] = reader["user_id"].ToString();
                    Session["EmailAddress"] = reader["email"].ToString();

                    if (reader["role"].ToString().Equals("0"))
                    {
                        Session["PermanentRole"] = "admin";
                    }
                    else if (reader["role"].ToString().Equals("2"))
                    {
                        Session["PermanentRole"] = "tutor";
                    }

                    Response.Redirect("~/portal.aspx");
                }
                else
                {
                    lblError.Text = "Your account has not been activated.  Please check your inbox and activate your account or reset your password by clicking the link above.";
                }
            }
            else
            {
                lblError.Text = "Incorrect password.";
            }
        }
        else
        {
            lblError.Text = "Username does not exist.";
        }

        reader.Close();
    }
    catch
    {
        lblError.Text = "Database connection error. Please try again.";
    }
    finally
    {
        conn.Close();
    }
}

修改后的代码：

protected void signIn()
{
    string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;

    using (MySqlConnection conn = new MySqlConnection(connStr))
    {
        using (MySqlCommand cmd = conn.CreateCommand())
        {
            string cmdText = "Select user_id, username, email, salt, hashed_pw, role, activated FROM users WHERE username=@username";
            cmd.CommandText = cmdText;
            cmd.Parameters.Add("@username", MySqlDbType.VarChar);
            cmd.Parameters["@username"].Value = txtUsername.Text;

            try
            {
                conn.Open();
                reader = cmd.ExecuteReader();

                if (reader.Read())
                {
                    string saltAndPwd = String.Concat(txtPassword.Text, reader["salt"].ToString());
                    string hashSaltAndPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");

                    if (hashSaltAndPwd.Equals(reader["hashed_pw"].ToString()))
                    {
                        if (reader["activated"].ToString().Equals("Y"))
                        {
                            Session["Username"] = reader["username"].ToString();
                            Session["Role"] = reader["role"].ToString();
                            Session["UserID"] = reader["user_id"].ToString();
                            Session["EmailAddress"] = reader["email"].ToString();

                            if (reader["role"].ToString().Equals("0"))
                            {
                                Session["PermanentRole"] = "admin";
                            }
                            else if (reader["role"].ToString().Equals("2"))
                            {
                                Session["PermanentRole"] = "tutor";
                            }

                            Response.Redirect("~/portal.aspx");
                        }
                        else
                        {
                            lblError.Text = "Your account has not been activated.  Please check your inbox and activate your account or reset your password by clicking the link above.";
                        }
                    }
                    else
                    {
                        lblError.Text = "Incorrect password.";
                    }
                }
                else
                {
                    lblError.Text = "Username does not exist.";
                }

                reader.Close();
            }
            catch
            {
                lblError.Text = "Database connection error. Please try again.";
            }
            finally
            {
                conn.Close();
            }
        }
    }

Answer 1

1) using语句将为您调用close，因此conn.Close();不是必需的。它等同于

MySqlConnection conn = new MySqlConnection(connStr)
try
{
     ....
}
finally
{
    conn.Close();
}

2)表单的陷阱

catch (Exception ex)
{
    throw ex;
}

在我能想到的任何情况下都不推荐。它有两个问题

，

• ，它除了重新抛出异常，什么也不做。任何捕获该异常的人都将看到该行上生成的错误，从而丢失有用的信息

Answer 2

您不需要finally { ...}，因为using将处理该连接。

您的问题是：

catch (Exception ex)
{
  throw ex;
}

当您想要记录异常但仍然抛出它时，简单地捕获并重新抛出没有任何意义。

但应该这样做：

catch (Exception ex)
{
  LogManager.Log(ex);
  throw;  //rethrow
}