Exception Handling in WCF Services

Q8M1 – SC Dudy Fathan Ali S.Kom

Distributed Application Development

Exception Handling in WCF Services

Dudy Fathan Ali, S.Kom (DFA)2017

CEP - CCITFakultas Teknik Universitas Indonesia

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Objectives


Define Exception Handling

Implement Exception Handling


Define Exception Handling


o Anticipating errors and providing error-handling code is known as exception handling.

o A WCF service and a client application communicate with each other by using SOAP.

o When an error occurs in the service, it needs to be communicated to the client in order to be handled properly.


Exception Communication by Using SOAP


o When an unhandled exception occurs in a WCF service, a default exception is thrown and the communication between the service and the client application is discontinued.

o The exception thrown by a WCF service should be converted into the SOAP format so that any client can easily interpret it.

o The SOAP specification is used to convert the exception into a standard format.

o The SOAP specification provides a fault element that may be present in the body of the message sent by a WCF service to a client application.


Exception Communication by Using SOAP


o The SOAP fault element is a standard format that contains the error message and information related to the error message.

o When WCF receives an unhandled exception at the service host, it faults the server channel and further communication between the clients and the service is halted.


Implementing Exception Handling


o Exception handling is implemented to handle all the possible exceptions.

o To implement exception handling in a WCF service, you can use the following classes of the System.ServiceModel namespace:

o The FaultException class

o The generic FaultException class


Using the FaultException Class


o The FaultException class is a base class that is used to handle exceptions in WCF.

o This class serializes the error messages that are thrown by a WCF service into the SOAP fault.

o The following code snippet shows the use of the FaultExceptionclass:

public int divideNumber(int num1, int num2)

{

if (num2 == 0)

{

throw new FaultException("Pembagi tidak boleh bernilai 0.");

}

int result = num1 / num2;

return result;

}


Using the FaultException Class


o The following code snippet shows how a client application can access the exception class:

public void divideClient()

{

ServiceReference.ServiceClient obj;

obj = new ServiceReference.ServiceClient();

try

{

int result = obj.divideNumber(10, 0);

Console.WriteLine(result);

}

catch (FaultException faultEx)

{

Console.WriteLine(faultEx.Message);

}

}


Using the Generic FaultException Class


o To enable a client application to access a user-defined class, you need to expose the class.

o To expose a user-defined exception class and send a customized message to a client application, you need to perform the following tasks:

o Define a user-defined exception class

o Define a FaultContract

o Throw a FaultException




o Define a user-defined exception class:

o While defining a user-defined exception class, you need to use the [DataContract] and [DataMember] attributes to expose the class and its members, as shown in the following code snippet:

[DataContract]

public class MyFaultException

{

[DataMember]

public string message;

}




o Define a [FaultContract]:

o The [FaultContract] attribute is defined to serialize the structure of the user-defined exception class.

o It indicates to a WCF service that a service’s WSDL should include the customized exception message sent to a client application.




o The following code snippet shows how to use the FaultContractattribute:

[ServiceContract]

public interface IService

{

[OperationContract]

[FaultContract(typeof(MyFaultException))]

int Divide(int numerator, int denominator);

}

[DataContract]

public class MyFaultException

{

[DataMember]

public string message;

}




o Throw a FaultException:

o To send a customized message in a SOAP fault format, you need to throw a FaultException exception that takes a user-defined class as a parameter.




o The following code snippet shows how to use the Generic FaultException class:

public int divideNumber(int num1, int num2)

{

if (num1 < num2)

{

MyFaultException objError = new MyFaultException();

objError.message = "Value of denominator can not be

greater than numerator";

throw new FaultException<MyFaultException>(objError);

}

int result = num1 / num2;

return result;

}




o The following code snippet shows how a client application can access the user-defined exception class:

public void divide()

{

ServiceRef.ServiceClient obj;

obj = new ServiceRef.ServiceClient();

try

{

int result = obj.divideNumber(10, 11);

Console.WriteLine(result);

}

catch (FaultException<ServiceRef.MyFaultException> faultEx)

{

Console.WriteLine(faultEx.Detail.message);

}

}


Thank You!Dudy Fathan Ali, S.Kom

[email protected]

mailto:[email protected]

Exception Handling in WCF Services

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