Exception Handling in ASP.NET Core Web API
Tags: webdev, programming, opensource, aspdotnet
Published: 2023-05-25 15:54:24

Capturing and managing exceptions that arise during the execution of HTTP requests is the responsibility of exception handling in the ASP.NET Core Web API. It enables you to manage exceptions in a centralized manner and give customers meaningful error answers. To handle errors in the ASP.NET Core Web API, follow these steps:

### 1. Global Exception Handling:
Implementing a global exception handler that catches any unhandled exceptions happening while the API is being used is one strategy. You can achieve this by developing a unique middleware component that detects errors and produces suitable answers. Here's an illustration:

```csharp
public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;

    public ExceptionMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            // Handle the exception and generate a response
            await HandleExceptionAsync(context, ex);
        }
    }

    private static Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        // Generate an error response based on the exception
        var response = new { error = exception.Message };
        var payload = JsonConvert.SerializeObject(response);
        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
        return context.Response.WriteAsync(payload);
    }
}
```

To register the middleware globally, add the following line to the `Configure` method in your `Startup.cs` file:

```csharp
app.UseMiddleware<ExceptionMiddleware>();
```

### 2. Exception Filters:
Utilizing exception filters, which let you handle exceptions for actions or controllers, is a different strategy. Implementing the "IExceptionFilter" interface allows you to make your own exception filter. As an illustration, consider the following.

```csharp
public class CustomExceptionFilter : IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        // Handle the exception and generate a response
        var response = new { error = context.Exception.Message };
        var payload = JsonConvert.SerializeObject(response);
        context.Result = new ContentResult
        {
            Content = payload,
            ContentType = "application/json",
            StatusCode = (int)HttpStatusCode.InternalServerError
        };
        context.ExceptionHandled = true;
    }
}
```

To apply the filter to a specific action or controller, use the `[ServiceFilter]` attribute:

```csharp
[ServiceFilter(typeof(CustomExceptionFilter))]
public class MyController : ControllerBase
{
    // ...
}
```

### 3. Custom Exception Types:
To describe particular problem circumstances in your API, you may also construct your own exception classes. You can handle these custom exceptions by throwing them and providing detailed error answers by utilizing the methods discussed above. As an illustration, consider the following.

```csharp
public class NotFoundException : Exception
{
    public NotFoundException(string message) : base(message)
    {
    }
}
```

In your action or middleware, you can throw the custom exception when needed:

```csharp
throw new NotFoundException("The requested resource was not found.");
```
These are some typical methods used in the ASP.NET Core Web API to manage errors. You can pick the one that best suits the needs and error-handling technique of your application.