Before we start with the recipe, we need access to the asynchronous web service. Since the BPEL processes also have the possibility to be exposed as the web services endpoints, we will use the asynchronous BPEL process for this recipe. That way we will also show how to call one BPEL process from another BPEL process.

The following steps show how to invoke the asynchronous web service from the BPEL process:

As with the synchronous web services, the asynchronous web services are also defined by the WSDL documents. If we check the port type, we spot the difference. Opposite to the synchronous web service, the asynchronous web service defines two port types as follows:

<wsdl:portType name = "HelloWorldAsyncProcess">
  <wsdl:operation name = "process">
    <wsdl:input message = "client:HelloWorldAsyncProcessRequestMessage"/>
  </wsdl:operation>
</wsdl:portType>
<wsdl:portType name = "HelloWorldAsyncProcessCallback">
  <wsdl:operation name = "processResponse">
    <wsdl:input message = "client:HelloWorldAsyncProcessResponseMessage"/>
  </wsdl:operation>
</wsdl:portType>

The port type definition comes out of the asynchronous nature of the web service. The two port types define the two one-way operations.

We call the asynchronous web service from BPEL with the <invoke> activity as follows:

<invoke name = "InvokeAsyncWS" inputVariable = "InvokeAsyncWS_process_InputVariable" partnerLink = "AsyncWS" portType = "ns1:HelloWorldAsyncProcess" operation = "process"/>

To receive the reply from the web service call, we use the <receive> activity as follows:

<receive name = "ReceiveAsyncWS" createInstance = "no" variable = "ReceiveAsyncWS_processResponse_InputVariable" partnerLink = "AsyncWS" portType = "ns1:HelloWorldAsyncProcessCallback" operation = "processResponse"/>

The <receive> activity is different from the <invoke> activity. Based on the WS-Addressing (address and conversation ID) mechanism, the <receive> activity picks up the correct message from the web service. Although we are using the <receive> activity, the BPEL process will wait until it receives the response. We need to define the name of the variable, partnerLink, portType, and operation.

We can also declare the fault in the asynchronous web service port type. Due to the one-way operation of the web service, we can only define the faults in the callback port type. Again, the faults are used when the web service cannot complete its operation successfully. The port type definition then states as follows:

<wsdl:portType name = "HelloWorldAsyncProcessCallback">
  <wsdl:operation name = "processResponse">
    <wsdl:input message = "client:HelloWorldAsyncProcessResponseMessage"/>
  </wsdl:operation>
  <wsdl:operation name = "processFault">
    <wsdl:input message = "client:ProcessFaultMessage"/>
  </wsdl:operation>
</wsdl:portType>

We see that the fault is modeled as an additional operation. The faults in the BPEL process are then modeled via the <pick> activity as follows:

<pick name = "PickMsg">
  <onMessage variable = "OnMessage_processResponse_InputVariable" partnerLink = "AsyncWS" portType = "ns1:HelloWorldAsyncProcessCallback" operation = "processResponse">
    <assign name = "AssignOK">
      <copy>
        <from expression = "string('OK')"/>
        <to variable = "outputVariable" part = "payload" query = "/client:processResponse/client:result"/>
      </copy>
    </assign>
  </onMessage>
  <onMessage variable = "OnMessage_processFault_InputVariable" partnerLink = "AsyncWS" portType = "ns1:HelloWorldAsyncProcessCallback" operation = "processFault">
    <assign name = "AssignFault">
      <copy>
        <from expression = "string('FAULT')"/>
        <to variable = "outputVariable" part = "payload" query = "/client:processResponse/client:result"/>
      </copy>
    </assign>
  </onMessage>
</pick>

The graphical presentation of the BPEL process is as follows:

Based on the type of the message returned from the asynchronous web service, we can decide on how to proceed with the BPEL process execution.

Another approach of modeling the asynchronous web service call from the BPEL process is usage of the event handlers to react on occurring of the message or alarm event.