Tutorials – ASP.Net Core

In Chapter 10 of our ASP.NET Core tutorial, we’ll delve into the essential topics of error handling and logging. Proper error handling is crucial for building robust web applications, as it ensures that your application gracefully handles unexpected situations and provides valuable feedback to users and developers. Additionally, effective logging is essential for troubleshooting issues and monitoring application behavior. In this chapter, we’ll cover the following key areas:

1. Error Handling in ASP.NET Core: Understanding the types of errors and exceptions that can occur in an ASP.NET Core application.

2. Handling Exceptions: How to handle exceptions and errors in ASP.NET Core, including global error handling and middleware.

3. Logging in ASP.NET Core: Exploring the built-in logging framework in ASP.NET Core, including log levels, providers, and configuration.

4. Implementing Error Pages: Creating custom error pages for various HTTP status codes to enhance the user experience.

5. Logging Best Practices: Tips and best practices for effective logging in ASP.NET Core, including structured logging and log management.

6. Error Tracking and Monitoring: An introduction to error tracking and monitoring solutions for production applications.

Let’s dive into each of these topics in detail:

10.1 Error Handling in ASP.NET Core

Errors and exceptions can occur at various stages of application execution. Understanding the types of errors is crucial for implementing effective error handling strategies.

Types of Errors:

1. Compile-Time Errors: These occur during code compilation and typically include syntax errors or type mismatches. Compile-time errors must be resolved before running the application.

2. Runtime Errors: Runtime errors occur during application execution and can include exceptions like null reference exceptions, divide-by-zero exceptions, or custom exceptions thrown by your code.

3. HTTP Errors: HTTP errors are returned to clients in response to HTTP requests. Common HTTP errors include 404 Not Found, 500 Internal Server Error, and 403 Forbidden.

4. Custom Errors: Custom errors are application-specific errors that you define to handle specific scenarios, such as validation errors or business logic errors.

10.2 Handling Exceptions

Handling exceptions gracefully is essential to ensure that your application remains stable and provides meaningful feedback to users. ASP.NET Core provides several mechanisms for handling exceptions:

10.2.1 Exception Middleware

You can create custom exception middleware to catch exceptions at the global level and handle them gracefully. For example, you can create middleware to log exceptions and return user-friendly error messages.

public class ExceptionMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<ExceptionMiddleware> _logger;
public ExceptionMiddleware(RequestDelegate next, ILogger<ExceptionMiddleware> logger) { _next = next; _logger = logger; }
public async Task InvokeAsync(HttpContext context)
    {
try
        {
await _next(context);
        }
catch (Exception ex)
        {
            _logger.LogError(ex, "An error occurred.");
            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
await context.Response.WriteAsync("An error occurred. Please try again later.");
        }
    }
}

In addition to global exception handling middleware, you can handle exceptions within your controller actions. You can use the [ExceptionHandler] attribute to define how specific exceptions should be handled at the action level.

[Route("api/[controller]")]
[ApiController]
public class ProductsController : ControllerBase
{
    [HttpGet("{id}")]
public ActionResult<Product> GetProduct(int id)
    {
var product = _productService.GetProduct(id);
if (product == null)
        {
return NotFound();
        }
return product;
    }
}

In this example, the GetProduct action checks if a product exists and returns a NotFound response if it doesn’t.

10.3 Logging in ASP.NET Core

Logging is a critical tool for troubleshooting issues, monitoring application behavior, and gaining insights into how your application is performing. ASP.NET Core provides a flexible and extensible logging framework that supports various log levels, log providers, and configuration options.

10.3.1 Log Levels

ASP.NET Core supports different log levels, allowing you to categorize log messages based on their severity. Common log levels include:

• Trace: The most detailed log level, typically used for debugging and tracing.
• Debug: Used for debugging information that should not be included in production logs.
• Information: General information about application behavior.
• Warning: Indicates potential issues that should be monitored.
• Error: Logs errors that need attention but don’t necessarily crash the application.
• Critical: Logs critical errors that require immediate attention.

10.3.2 Log Providers

ASP.NET Core supports various log providers, which are responsible for writing log messages to different destinations. Common log providers include:

• Console Logging: Logs messages to the console (useful during development and debugging).
• File Logging: Writes log messages to log files on disk (useful for production logging).
• EventLog Logging: Logs messages to the Windows Event Log (for Windows-based applications).
• Third-Party Providers: You can integrate third-party logging providers like Serilog or NLog.

10.3.3 Logging Configuration

Logging configuration in ASP.NET Core can be done in the Startup.cs file using the appsettings.json file or through code. You can specify log levels, log providers, and log output formats.

public void ConfigureLogging(ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole();
    loggerFactory.AddFile("logs/myapp-{Date}.txt");
// Additional configuration
}

10.4 Implementing Error Pages

Custom error pages enhance the user experience by providing user-friendly error messages when issues occur. You can create custom error pages for various HTTP status codes, such as 404 Not Found, 500 Internal Server Error, and others.

Custom Error Pages Example:

1. Create custom error pages (e.g., 404.html, 500.html) in your project’s wwwroot folder.

2. Configure error pages in the Startup.cs file:

app.UseStatusCodePagesWithReExecute("/error/{0}");
app.UseExceptionHandler("/error/500");
app.UseStatusCodePagesWithRedirects("/error/{0}");

10.5 Logging Best Practices

Effective logging is essential for diagnosing and troubleshooting issues in your application. Here are some logging best practices:

• Use Structured Logging: Log structured data (e.g., JSON) to enable easy parsing and analysis of log entries.

• Log Important Events: Log important application events, such as user actions, system events, and errors.

• Avoid Excessive Logging: Be selective in what you log to avoid flooding your logs with unnecessary information.

• Use Log Levels Appropriately: Assign log levels based on the severity of the message.

• Secure Log Data: Avoid logging sensitive information like passwords or personal data.

• Log Exceptions: Include exception details, including stack traces, when logging errors.

10.6 Error Tracking and Monitoring

In production environments, it’s essential to track and monitor errors and exceptions to proactively address issues and ensure the application’s stability. Various error tracking and monitoring solutions are available, such as:

• Application Insights: A service provided by Azure for monitoring and diagnostics of applications.
• Sentry: An open-source error tracking platform that supports multiple languages, including .NET Core.
• ELK Stack: Elasticsearch, Logstash, and Kibana provide a powerful log management and analytics solution.

Integrating these solutions into your ASP.NET Core application can help you gain valuable insights into application behavior and identify and resolve issues quickly.

10.7 Conclusion of Chapter 10

In Chapter 10, we’ve explored the critical topics of error handling and logging in ASP.NET Core. Effective error handling ensures that your application gracefully handles unexpected situations, providing a better user experience and making troubleshooting easier. Logging, on the other hand, is essential for monitoring application behavior and diagnosing issues in production.

Key takeaways from this chapter include:

• Understanding the types of errors that can occur in an ASP.NET Core application.
• Implementing global error handling middleware and handling exceptions within controllers.
• Utilizing the built-in logging framework in ASP.NET Core for recording application events.
• Configuring log levels, log providers, and log output formats.
• Creating custom error pages to enhance the user experience.
• Following best practices for effective logging, including structured logging.
• Exploring error tracking and monitoring solutions for production environments.

With a solid understanding of error handling and logging, you’ll be better equipped to build and maintain robust and reliable ASP.NET Core applications. In the upcoming chapters, we’ll explore more advanced topics and real-world application development techniques to further enhance your skills as a web developer.