Chapter 5 Client Design

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have a strategy for your client application to deal with these situations. For example,

with these types of errors, it may be useful to have the client application prompt the

user to retry the operation or redirect the user to an alternative service, if possible.

Many times the only solution is to display the exception occurrence to the end user.

Sometimes it may be appropriate to translate the system exception to an unchecked

exception and devise a global way to handle them. The exact solution is particular to

each application and situation.

System exceptions, which the client receives as 

RemoteException

, arise from

a variety of reasons. Often system exceptions happen because of network failures

or server errors. They also may be the result of a SOAP fault. Since a

RemoteException

 usually contains an explanation of the error, the application can

use that message to provide its own error message to the user and can prompt the

user for an appropriate action to take. If an EJB component client is doing its work

on behalf of a Web tier client, the EJB client should throw an exception to the Web

tier client. The Web tier client notifies the user, giving the user a chance to retry

the action or choose an alternative action.

When communicating using stubs, most system exceptions involve network

issues or the configuration of the stub. A configuration error is thrown from the

_getProperty

 and 

_setProperty

 methods as a 

javax.xml.rpc.JAXRPCException

and indicates a property name that is not supported or is invalid, a property setting

value that is not allowed, or a type mismatch.

When using a dynamic proxy, the 

getPort

 method may throw a

javax.xml.rpc.ServiceException

 if the WSDL document has insufficient meta 

data to properly create the proxy.

A client may receive several different exceptions when using the DII 

Call

interface. A client may receive a 

RemoteException

 if a network failure occurs. A

client may also be thrown a 

javax.xml.rpc.JAXRPCException

 if the 

Call

 set

methods use invalid property names or try to set properties with invalid values.

For example, a client application accessing an order tracking service may

want to use an alternative service or endpoint if it receives a 

RemoteException

indicating the unavailability of the service. 

Web components may leverage the servlet error messaging system and map

the 

RemoteException

 to some exception handling instructions in the 

web.xml 

file.

The client can throw its own 

javax.servlet.ServletException

 and can display a

general application error message. It is possible to extend 

ServletException

 to

create a set of application specific exceptions for different errors. It may also use

the file to define a specific error JSP to handle the error, as shown in Code

Example 5.14.