Using Dynamic Partner Links and Dynamic Addressing

When you are designing an application, you may need to configure certain services whose endpoints (addresses) are not known beforehand, or it may be necessary to change an endpoint reference while the application is running. The Dynamic Partner link feature allows you to dynamically assign an endpoint reference to the partner link. This means that you can use one partner link for subsequent calls to different web-services (provided that the services use the same interface).

There are several different ways to construct the end point information in BPEL. To deliver the address information to the partner link you can use standard a Assign activity and the BPEL Mapper. In the following examples the endpoint address follows the WS-Addressing schema. Refer to WS-Addressing standard (WS-A).

Using a Literal to Construct an Endpoint

The BPEL literal syntax can be used to define an endpoint address and assign it to a partner link. The following code sample shows a BPEL literal used to define an HTTP endpoint assigned to a partner link.

<bpws:assign name="Assign2">
    <bpws:copy>
            <bpws:from>
                    <bpws:literal>
                            <sref:service-ref>
                                    <ns1:EndpointReference>
                                            <wsa:Address>
                                                http://localhost:8080/StockQuoteService
/StockQuotePort
                                            </wsa:Address>
                                            <wsa:ServiceName PortName="stockQuotePort">
                                                ns3:stockQuoteService>
                                            </wsa:ServiceName>
                                    </ns1:EndpointReference>
                            </sref:service-ref>
                       </bpws:literal>
                </bpws:from>
                bpws:to partnerLink="plStockQuote"/>
        </bpws:copy>
</bpws:assign>

In this scenario, you are invoking a partner link that is associated with a SOAP (HTTP) endpoint. That partner link, on the binding side of the application, acts as a proxy for BPEL to the external world.

In this example, we have an XML fragment that displays an Assign activity. The Assign has a copy and points to a literal address inline. When you invoke the service, you can assign a different address as a variable value in the invoke properties. In addition to assigning value to variable, you also assign a value to the partner link. Then, when the service is invoked, the HTTP Binding Component stops using the deployment address and instead uses the address that you just assigned.

The partner link "plStockQuote" could be subsequently used in an invoke.

Note that the WS-A defined schema object should be wrapped in an element called service-ref, that is defined in the BPEL. For more information about using the service-ref wrapper, refer to the BPEL Specification, section 6.3.

Using an Existing Partner Link's Endpoint

The endpoint of one partner link can be assigned to another partner link. The following BPEL Mapping and code sample show how the partnerRole endpoint of PartnerLink1 is copied to PartnerLink2.

Mapping the PartnerLink1 partnerRole to PartnerLink2 generates the following source code.

<assign name="Assign2">
     <copy>
         <from partnerLink="PartnerLink1" endpointReference="partnerRole"/>
         <to partnerLink="PartnerLink2"/>
     </copy>
 </assign>

In this example, PartnerLink1 is associated with a SOAP address. Instead of using that address, you want to use PartnerLink2. You send the address of PartnerLink1 to PartnerLink2. PartnerLink1 partnerRole endpoint is copied to PartnerLink2.

PartnerLink2 can also be used in subsequent invokes.

Using an Incoming Message to Extract the Endpoint

To extract an endpoint address from an incoming message, the message must be defined with the endpoint schema as part of the message. The following code sample show one way that this can be done.

<types>
    <xsd:schema targetNamespace="http://j2ee.netbeans.org/wsdl/dynamicPL">
        <xsd:import namespace="http://schemas.xmlsoap.org/ws/2004/08/addressing" 
        schemaLocation="http://schemas.xmlsoap.org/ws/2004/08/addressing/"/>
            
    </xsd:schema>
</types>
<message name="dynamicPLOperationRequest">
    <part name="part1" element="wsa:EndpointReference"/>
</message>

Note that the prefix wsa is defined to point to http://schemas.xmlsoap.org/ws/2004/08/addressing.

Use this message variable to assign the endpoint to a partner link at runtime. A special BPEL mapper function, "Wrap with Service Reference" makes it easy to map the WS-A message to a partner link, as demonstrated below.

Choosing the BPEL Mapper option Wrap with Service Reference adds the doXslTransform method box to the Mapper canvas.

The doXslTransform Method box generates the BPEL doXslTransform() function, as shown in the code sample below.

<assign name="Assign1">
    <copy>
        <from>ns0:doXslTransform('urn:stylesheets:wrap2serviceref.xsl', 
$DynamicPLOperationIn.part1)</from>
        <to partnerLink="PartnerLink1"/>
    </copy>
</assign>

The stylesheet for the transformation is already defined by the editor.

Using a Database Query to Provide an Endpoint

Expanding on the last example, you can also have a BPEL service do a dynamic addressing invocation, with the address coming from a database.

You start with a composite application that is triggered by something such as a input file. You do not want to use the address that is directly assigned to the file, so you do a database query or database select for the address.

The composite application triggers the Database Binding Component to do a simple select from a table that contains addresses. The composite application takes the results from the database query and puts it into the BPEL Mapper and maps the query result to the variable where you normally put your dynamic SOAP address. The Mapper assigns this address to the partner link.

Sending Service Endpoint References

A service can send its own endpoints, that can then be used as call back addresses, using the following type of mapping.

The PartnerLink1 myRole is mapped to the DynamicPLOperationIn part1. This generates the following code sample.

<assign name="Assign2">
    <copy>
        <from partnerLink="PartnerLink1" endpointReference="myRole"/>
        <to variable="DynamicPLOperationIn" part="part1"/>
    </copy>
</assign>

When the variable “DynamicPLOperationIn” is used in subsequent invokes in the BPEL, the endpoint information is passed on to the partner.