Setting up a errors and exceptions handling in a system is a big architectural challenge. If you want to listen and discuss about different kind of errors, affected groups of people, error categorization and error context this session is for you! In this session we will cover: - theory of errors; - error and exception handling on architectural level; - process mining over application log files; Code: https://github.com/mnikolovski/CC

1. Ready
Marjan Nikolovski
Father, Dev, CEO/Emit Knowledge
Down the rabbit hole
Error handling examined
try {
}
// Twitter: @m4rjann
// Blog: emitknowledge.com/research-labs

2. Ready

3. Ready
Agenda
• Error theory;
• Error types;
• Handling error per type;
• Responsible sides;
• Error handling strategies;
• Error handling for business logic;
• Error handling for client;
• Error handling for web applications;
• Log analytics;

4. Ready
ERROR IS AN ANY INTERUPTION THAT STOPS THE
SYSTEM TO EXECUTE A BUSINESS CONTEXT

5. Ready
A system must have a good strategy when it comes to error handling
Most of the code in a solution is trying to handle different types of errors and
exceptions
It is easy to specify and write code to make the system operable.
Hard times come when trying to predict what can go wrong

6. Ready
Bugs, issues we can’t predict nor control.
Ex: Stackoverflow, Nullpointer...
Error types
using System;
class Program
{
static void Main()
{
User appUser = DomainServices.User.GetByUsername(@“marjann”);
Console.WriteLine(appUser.Email);
}
}

7. Ready
Error from invalid input.
Ex: We expect integer value, the user enters some random characters...
Error types
using System;
class Program
{
static void Main()
{
var userIdInput = Console.ReadLine();
int id = int.Parse(userIdInput);
Console.WriteLine(id);
}
}

8. Ready
Infrastructural problems.
Ex: Missing write permissions on server, full disk, DB not available...
Error types
using System;
class Program
{
static void Main()
{
var user = UserRepository.GetByUsername(@”marjann”);
Console.WriteLine(user.Email);
}
}

9. Ready
Bugs are system problems that we can’t handle unless we apply a patch.
So what types of errors we
can handle?
Invalid data entry is a system problem that we can handle proactively.
If we have infrastructural problems, the system should be able to notify the
system administrators.

10. Ready
End clients who are using the system.
Responsible sides
System administrators.
Software developers.

11. Ready
Software developers.
Who should handle the
bugs?

12. Ready
Global – architectural decision on system level.
Error handling strategies
Local-contextual – handling errors in a process/method/action.

13. Ready
КЛИЕНТ/КОРИСНИЧКИ
ИНТЕРФЕЈС
БИЗНИС ЛОГИКА
ПОДАТОЧНО РЕПОЗИТОРИ
АПИ СЕРВИСИ
ЕКСТЕРНИ СЕРВИСИ
СПРАВУВАЊЕ
СО ГРЕШКИ
ERROR
HANDLING
Web/Mobile/Device REST API SERVICES
BUSINESS LOGIC
DATA REPOSITORY EXTERNAL SERVICES

14. Ready
Global perspective of the system.
GLOBAL STRATEGY
Centralized error handling.
We want detailed error instead of wrapped exception.
We want execution details.
We want unified error messages.

15. Ready
GLOBAL STRATEGY
Internally, a system should not hide the exceptions.
Ex: User.IsExistingUsername(“marjann”) -> DbConnetionException != false
Externally, a system should always be transparent and should support unified
error information when an error occurs.
Ex: Invalid username, Username is not valid!?

16. Ready
Say hello to the local context.
What if we can retry?
Use local context as an exception to the rule!
We can’t predict and handle all of the errors, but we must keep the system alive.
Exception to the rule: If it does not work fake it!

17. Ready
Unification of errors, codes and groups.
Error handling for business
logic
Information about an error(Error Info) against Exceptions.
Enrich an error with data for logging aspect.

18. Ready
Demo

19. Ready
Be transparent and show enough information to the end user.
Error handling for client

20. Ready
Demo

21. Ready
Error message localization.
Error handling for web
applications
Transferring error information back to the app.

22. Ready
Demo

23. Ready
Who, What, How, Where, When?
Log analytics
PROM – tool for process mining.
We should be able to answer:
- How our system is used?
- Where our system perform slow?
- Parameters of execution?
- Patterns of execution?

24. Ready

25. Ready
catch(PPTException up){
}
Logger.Log(“QUESTIONS?”, up);
throw up;