Exception that throws another Exception

Question

I have a CustomException class, that is a wrapper on top of Exception class. This is the main class that i use when i handle Exceptions.

public class CustomException : Exception
{
    public string ErrorMessage { get; private set; }
    public HttpStatusCode HttpStatusCode { get; private set; }

    public CustomException(string errorMessage)
        : this(errorMessage, HttpStatusCode.InternalServerError)
    { }

    public CustomException(string message, HttpStatusCode httpStatusCode)
    {
        ErrorMessage = message;
        HttpStatusCode = httpStatusCode;
    }
}

When i want to throw an exception, i use throw CustomException() method.

However, i want to create some wrappers on top of this CustomException() as well, for example:

public class ApplicationNotFoundException : Exception
{
    public ApplicationNotFoundException(Application application)
    {
        string message = string.Format(@"Application ""{0}"" was not found", application.ApplicationName);
        throw new CustomException(message, HttpStatusCode.NotFound);
    }
}

And i throw exception line this: throw new ApplicationNotFoundException(application)

Basically i am throwing an Exception from another Exception.

Is this approach bad?

Steve · Answer 1 · 2013-05-11T10:20:46.963

Let the user of your ApplicationNotFoundException decide when it is appropriate to throw.
Don't do it in the constructor of your ApplicationNotFoundException.

Instead derive your ApplicationNotFoundException from CustomException

public class ApplicationNotFoundException : CustomException 
{
    public ApplicationNotFoundException(Application application)
    {
        string message = string.Format(@"Application '{0}' was not found", application.ApplicationName);
        base.ErrorMessage = message
        base.HttpStatusCode = HttpStatusCode.NotFound;
    }
}

public class CustomException : Exception
{
    public string ErrorMessage { get; internal set; }
    public HttpStatusCode HttpStatusCode { get; internal set; }

    public CustomException(string errorMessage)
        : this(errorMessage, HttpStatusCode.InternalServerError)
    { }

    public CustomException(string message, HttpStatusCode httpStatusCode)
    {
        ErrorMessage = message;
        HttpStatusCode = httpStatusCode;
    }
}

This means i first initialize the `ApplicationNotFoundException` class, then i throw it? — Catalin, May 11 '13 at 10:29
Yes, when you need to throw the exception you call `throw new ApplicationException(appInstance);` — Steve, May 11 '13 at 12:10

score 2 · Accepted Answer · answered May 11 '13 at 10:13

2

This is basically not the approach to use exceptions.
Creating custom exceptions serves your custom needs, that if built-in exceptions can't handle this.
There are some ways for you:

Create a hierarchy of exceptions, where CustomException is your "base" class and ApplicationNotFoundException is a derived one, this is the preferred way of specializing.

or

Embed the information you need into your custom exception-classes (create small structs if you just want to send some information and don't need to work on the particular objects themselves)

EDIT

Also, which is very important, consider stack unwinding as a factor of efficiency. Throwing an exception forces the call stack to be unwound, which takes a little time, too!

You can do it your way, of course, but it might tighten things a little up, which could be unnecessary.

For some background, consider MSDN.

answered May 11 '13 at 10:13

bash.d

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+1, ApplicationNotFoundException should derive from CustomException – Nick Patsaris May 11 '13 at 10:18
@bash.d: The only downside of having `ApplicationNotFoundException` deriving from `CustomException` is that i cannot create the exception text inside the body of `ApplicationNotFoundException` constructor – Catalin May 11 '13 at 10:20
@RaraituL You can't?? Why not?? – bash.d May 11 '13 at 10:22
@bash.d I've just seen this [question](http://stackoverflow.com/questions/12051/calling-base-constructor-in-c-sharp). It looks like i can do it after all – Catalin May 11 '13 at 10:26
@RaraituL See, everything is fine! :) – bash.d May 11 '13 at 10:27

Salomonder · Answer 3 · 2013-05-11T10:47:50.000

A common scenario is to rethrow your more specific exception type rather in the catch block than in the constructor:

try {
    ... // Try to find application
}
catch(ApplicationNotFoundException ex) {
    var message = ...;
    throw new CustomException(message, HttpStatusCode.NotFound);
}

When rethrowing a different exception, you can set the InnerException property with the original exception to aid debugging.

Exception that throws another Exception

3 Answers3