Catch Custom Exception from ASMX Web Service

Question

I have a web service in which I have created a custom exception. Let's say the name of this exception is InvalidContractException.

What I would like to do is if a specific step occurs, I want to throw this exception. However, I can't figure out how the client would catch the InvalidContractException in order to handle it properly.

This is an ASP.Net Web Service written in C#

Answer 1

You can't do this:

1. Web services do SOAP Faults. Exceptions are platform-specific.
2. When an exception is unhandled in an ASMX web service, .NET will translate it into a SOAP Fault. The details of the exception are not serialized.
3. In an ASMX client, a SOAP fault will be translated into a SoapException.

ASMX web services do not have proper support for SOAP Faults. There is no way to get any exception other than a SoapException on the client side.

Yet another reason to upgrade to WCF.

---

As an example of what you can't do with ASMX, here's how WCF works. WCF allows you to specify, for each web service operation, which faults it can return:

[ServiceContract]
public interface IMyServiceContract
{
    [FaultContract(typeof(IntegerZeroFault))]
    [FaultContract(typeof(SomeOtherFault))]
    [OperationContract]
    public string GetSomeString(int someInteger);
}

[DataContract]
public class IntegerZeroFault
{
    [DataMember]
    public string WhichInteger {get;set;}
}

[DataContract]
public class SomeOtherFault
{
    [DataMember]
    public string ErrorMessage {get;set;}
}

public class MyService : IMyServiceContract
{
    public string GetSomeString(int someInteger)
    {
        if (someInteger == 0) 
            throw new FaultException<IntegerZeroFault>(
                new IntegerZeroFault{WhichInteger="someInteger"});
        if (someInteger != 42)
            throw new FaultException<SomeOtherFault>(
                new SomeOtherFault{ErrorMessage ="That's not the anaswer"});
        return "Don't panic";
    }
}

A WCF client can then catch FaultException<SomeOtherFault>, for instance. When I've tried this with a Java client, it was able to catch SomeOtherFault, which IBM Rational Web Developer created to derive from the Java Exception class.