Fault handlers define how the BPEL process service component responds when target services return data other than what is normally expected (for example, returning an error message instead of a number). An example of a fault handler is where the web service normally returns a credit rating number, but instead returns a negative credit message.

Figure 12-1 provides an example of how a fault handler sets a credit rating variable to -1000.

The code segment in the following example defines the fault handler for this operation in the BPEL file:

<faultHandlers>
     <catch faultName="services:NegativeCredit" faultVariable="crError">
      <assign name="crin">
         <copy>
           <from expression="-1000">
           </from>
           <to variable="input" part="payload"
               query="/autoloan:loanApplication/autoloan:creditRating"/>
         </copy>
       </assign>
     </catch>
</faultHandlers>

The faultHandlers tag contains the fault handling code. Within the fault handler is a catch activity, which defines the fault name and variable, and the copy instruction that sets the creditRating variable to -1000.

When you select web services for the BPEL process service component, determine the possible faults that may be returned and set up a fault handler for each one.