code duplication in try catch block

Question

Is there a better way to catch exceptions? I seem to be duplicating a lot of code. Basically in every controller I have a catch statement which does this:

try
{
     Do  something that might throw exceptions.
}
catch (exception ex)
{
     Open database connection
     Save exception details.
     If connection cannot be made to the database save exception in a text file.
}

I have 4 controllers and around 5-6 actions methods in each controller which is a lot of code duplication. How can I trim down on the amount of line in the try catch statement above?

Answer 1

You could make use of Extension methods here.

Create an extension method in a new class.

public static class ExtensionMethods
{
    public static void Log(this Exception obj)
    {
        // log your Exception here.
    }
}

And use it like:

try
{
}
catch (Exception obj)
{
    obj.Log();
}

Answer 2

You don't need to put try/catch blocks on every method. That's tedious and painful! Instead you can use the Application_Error event of Global.asax for logging the exceptions. The code below is the sample implementation which can be used to catch exceptions that occur in your web application.

protected void Application_Error(object sender, EventArgs e)
{
    var error = Server.GetLastError();
    if (!string.IsNullOrWhiteSpace(error.Message))
    {
        //do whatever you want if exception occurs
        Context.ClearError();
    }
}

I would like also to stress that "Handled exception" especially trying to put try/catch blocks on most methods is one of the "Top 3 silent performance killers for IIS / ASP.NET apps" as explained in this blog http://mvolo.com/fix-the-3-high-cpu-performance-problems-for-iis-aspnet-apps/

Answer 3

What you are trying to do is called a cross-cutting concern. You are trying to log any error that happens anywhere in your code.

In ASP.NET MVC cross-cutting concerns can be achieved by using Filters. Filters are attributes that can be applied globally, to a controller or to a method. They run before an action method executes or after it.

You have several types of filters:

• Authorization filters, they run to check if the user is allowed to access a resource.
• Action filters, these run before and after an action method executes.
• Result filters, these can be used to change the result of an action method (for example, add some extra HTMl to the output)
• Exception filters run whenever an exception is thrown.

In your case, you are looking for exception filters. Those filters only run when an exception happens in in an action method. You could apply the filter globally so it will automatically run for all exceptions in any controller. You can also use it specifically on certain controllers or methods.

Here in the MSDN documentation you can find how to implement your own filters.

Answer 4

Personally, since I greatly dislike try/catch blocks, I use a static Try class that contains methods that wrap actions in reusable try/catch blocks. Ex:

public static class Try {
   bool TryAction(Action pAction) {
      try {
         pAction();
         return true;
      } catch (Exception exception) {
         PostException(exception);
         return false;
      }
   }

   bool TryQuietly(Action pAction) {
      try {
         pAction();
         return true;
      } catch (Exception exception) {
         PostExceptionQuietly(exception);
         return false;
      }
   }

   bool TrySilently(Action pAction) {
      try {
         pAction();
         return true;
      } catch { return false; }
   }

   // etc... (lots of possibilities depending on your needs)
}

Answer 5

I have used a special class in my applications that is called ExceptionHandler, in the class that is static I have some methods to handle application's exceptions. It gives me an opportunity to centralize exception handling.

public static class ExceptionHandler
{
    public static void Handle(Exception ex, bool rethrow = false) {...}
    ....   
}

In the method you can log the exception, rethrow it, replace it with another kind of exception, etc.

I use it in a try/catch like this

try
{
    //Do something that might throw exceptions.
}
catch (exception ex)
{
    ExceptionHandler.Handle(ex);
}

As Wouter de Kort has rightly stated in his answer, it is cross-cutting concern, so I've put the class in my Application Layer and have used it as a Service. If you defined the class as an interface you would be able to have different implementations of it in different scenarios.

Answer 6

Also you can use Singleton pattern:

sealed class Logger
{
    public static readonly Logger Instance = new Logger();

    some overloaded methods to log difference type of objects like exceptions
    public void Log(Exception ex) {}
    ...
}

And

Try
{
}
Catch(Exception ex)
{
    Logger.Instance.Log(ex);
}

Edit Some peoples don't like Singleton for reasonable grounds.instead of singleton we can use some DI:

class Controller
{
    private ILogger logger;

    public Controller(ILogger logger)
    {
        this.logger = logger;
    }
}

And use some DI library that will inject one instance of ILogger into your controllers.

Answer 7

I like the answers suggesting general solutions, however I would like to point out another one which works for MVC. If you have a common controller base (wich you should anyways, it's a Best Practice IMO). You can simply override the OnException method:

public class MyControllerBase : Controller
{
    protected override void OnException(ExceptionContext filterContext)
    {
        DoSomeSmartStuffWithException(filterContext.Exception);
        base.OnException(filterContext);
    }
}

Then simply inherit your normal controllers from your common base instead of Controller

public class MyNormalController : MyControllerBase 
{
    ...

If you like this you can check out the Controller class for other handy virtual methods, it has many.

Answer 8

In ASP .NET MVC you can implement your own HandleErrorAttribute to catch all the exceptions that occur in all controllers:

public class CustomHandleErrorAttribute : HandleErrorAttribute
{
    public override void OnException(ExceptionContext filterContext)
    {
      var ex = filterContext.Exception;

      //     Open database connection
      //     Save exception details.
      //     If connection cannot be made to the database save exception in a text file.
    }
 }

Then register this filter:

public class FilterConfig
{
    public static void RegisterGlobalFilters(GlobalFilterCollection filters)
    {
       filters.Add(new CustomHandleErrorAttribute());
    }
 }

And of-course call the register method on application start-up:

public class MvcApplication : HttpApplication
{
    protected override void OnApplicationStarted()
    {
       // ...
       FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
       // ...
    }
}

Wouter de Kort has already explained the concept behind this in his answer.