Best Practices for Exception Handling in .NET Core

17 October 2017

Exception handling is a critical aspect of building robust and reliable applications. In .NET Core, handling exceptions correctly can improve the user experience, help you maintain the stability of your application, and make it easier to track and debug issues. In this post, we’ll discuss best practices for exception handling in .NET Core, including how to create custom exception filters to streamline the process.

1. Why Is Exception Handling Important?

Handling exceptions properly ensures that your application remains responsive and provides clear feedback to users when something goes wrong. Unhandled exceptions can cause your application to crash, leading to a poor user experience and potentially losing important data.

Good exception handling practices make it easier to isolate and fix bugs, improve maintainability, and keep your application running smoothly under various conditions.

2. Basic Exception Handling in .NET Core

The simplest form of exception handling in .NET Core is done using the try, catch, and finally blocks. The try block contains the code that might throw an exception, while the catch block handles the exception. The finally block, which is optional, is used for clean-up actions, like closing database connections.

Here’s an example of basic exception handling:

public IActionResult GetData(int id)
{
    try
    {
        // Code that might throw an exception
        var data = _dataService.GetDataById(id);
        return Ok(data);
    }
    catch (ArgumentException ex)
    {
        // Handle specific exception
        return BadRequest("Invalid argument: " + ex.Message);
    }
    catch (Exception ex)
    {
        // Handle general exceptions
        return StatusCode(500, "An error occurred: " + ex.Message);
    }
    finally
    {
        // Clean-up code (optional)
        _logger.LogInformation("GetData executed.");
    }
}

In this example:

The catch block handles ArgumentException and generic Exception types.
The finally block ensures that certain actions (e.g., logging) are always performed, even if an exception is thrown.

3. Best Practices for Exception Handling

While basic exception handling is straightforward, it’s important to follow best practices to ensure that exceptions are managed in a scalable and maintainable way. Let’s look at some of these best practices:

a. Use Specific Exceptions

When handling exceptions, always catch the most specific exceptions first. Catching general exceptions, such as Exception, should be avoided when possible because it can mask other issues and make debugging harder. If you know the exact exceptions your code might throw (like ArgumentException or FileNotFoundException), catch them individually.

catch (FileNotFoundException ex)
{
    // Handle file not found error
}
catch (UnauthorizedAccessException ex)
{
    // Handle unauthorized access error
}

b. Don’t Catch Exceptions You Can’t Handle

If you can’t recover from an exception or don’t have any meaningful way to handle it, let it propagate. Catching and rethrowing the exception (or catching it and doing nothing) can hide important errors and complicate the debugging process.

catch (Exception ex)
{
    // Log the exception, but don't swallow it
    _logger.LogError(ex, "Unhandled error occurred");
    throw; // Re-throw the exception
}

c. Return Meaningful Responses

When an exception occurs, it’s important to return a meaningful and helpful response to the user or consumer of your API. Providing specific error codes and messages helps users understand what went wrong and how they might fix the issue.

catch (NotFoundException ex)
{
    return NotFound($"Item with ID {id} not found.");
}
catch (ValidationException ex)
{
    return BadRequest($"Validation failed: {ex.Message}");
}

d. Log Exceptions for Debugging and Monitoring

Logging is essential for monitoring and debugging exceptions in production environments. Use a logging framework, like Serilog or NLog, to log exceptions with details about the context and environment in which they occurred. This will help you identify recurring issues and improve your app’s stability.

catch (Exception ex)
{
    _logger.LogError(ex, "An unexpected error occurred.");
    throw;
}

4. Creating Custom Exception Filters

In some cases, you might want to centralize exception handling logic in your application instead of repeating the same try-catch blocks in each action. .NET Core allows you to create exception filters to catch exceptions globally or for specific controllers/actions.

a. What Is an Exception Filter?

An exception filter is a piece of code that runs when an unhandled exception occurs during the execution of an action. Exception filters allow you to handle exceptions in a centralized way and provide a consistent response across your application.

b. Creating a Custom Exception Filter

Here’s how you can create a custom exception filter in .NET Core to handle exceptions across multiple actions:

Create the filter class:

public class CustomExceptionFilter : IExceptionFilter
{
    private readonly ILogger<CustomExceptionFilter> _logger;

    public CustomExceptionFilter(ILogger<CustomExceptionFilter> logger)
    {
        _logger = logger;
    }

    public void OnException(ExceptionContext context)
    {
        // Log the exception
        _logger.LogError(context.Exception, "An error occurred in the action.");

        // Modify the response
        context.Result = new ObjectResult(new { message = "An unexpected error occurred." })
        {
            StatusCode = 500
        };
    }
}

public void ConfigureServices(IServiceCollection services)
{
    // Add the custom exception filter globally
    services.AddControllers(options =>
    {
        options.Filters.Add<CustomExceptionFilter>();
    });
}

Now, the CustomExceptionFilter will be applied to all actions, and any unhandled exceptions will be caught, logged, and a consistent response will be returned.

c. Using Exception Filters for Specific Controllers/Actions

If you want to apply the exception filter to specific controllers or actions, you can use the ServiceFilter or TypeFilter attributes:

[ServiceFilter(typeof(CustomExceptionFilter))]
public class MyController : ControllerBase
{
    // Actions here
}

This allows you to apply your exception filter selectively, making it easier to maintain and customize.

5. Conclusion

In this post, we’ve explored best practices for exception handling in .NET Core and the creation of custom exception filters to improve error handling and maintainability. By following these best practices and using exception filters, you can build more resilient applications, simplify error management, and improve the overall user experience.

Remember, exception handling is an ongoing practice, and as your application grows, it will be important to revisit and refine your error handling strategies.

Happy coding!