There are different ways to achieve asynchronous interaction in Oracle SOA Suite. In this blog article, I’ll explain some differences between WS-Addressing and using correlation sets (in BPEL but also mostly valid for BPM). I’ll cover topics like how to put the Service Bus between calls, possible integration patterns and technical challenges.
I will also shortly describe recovery options. You can of course depend on the fault management framework. This framework however does not catch for example a BPEL Assign activity gone wrong or a failed transformation. Developer defined error handling can sometimes leave holes if not thoroughly checked. If a process which should have performed a callback, terminates because of unexpected reasons, you might be able to manually perform recovery actions to achieve the same result as when the process was successful. This usually implies manually executing a callback to a calling service. Depending on your choice of implementation for asynchronous interaction, this callback can be easy or hard.
WS-Addressing
The below part describes a WS-Addressing implementation based on BPEL templates. There are alternatives possible (requiring more manual work) such as using the OWSM WS-Addressing policy and explicitly defining a callback port. This has slightly different characteristics (benefits, drawbacks) which can be abstracted from the below description. BPM has similar characteristics but also slightly different templates.
When creating a BPEL process, you get several choices for templates to base a new process on. The Synchronous BPEL template creates a port which contains a reply (output message) in the WSDL. When you want to reply, you can use the ‘Reply’ activity in your BPEL process. The activity is present when opening your BPEL process after generation by the template, but you can use it in other locations, such as for example in exception handlers to reply with a SOAP fault. If you want to call a synchronous service, you only need a single ‘Invoke’ activity.
The output message is not created in the WSDL when using the One Way or Asynchronous templates. Also when sending an asynchronous ‘reply’, you have to use the Invoke activity in your BPEL process instead of the ‘Reply’ activity. One Way BPEL process and Asynchronous BPEL process templates are quite similar. The Asynchronous template creates a callback port and message. The ‘Invoke’ activity to actually do the asynchronous callback is already present in the BPEL process after it has been generated based on the template. The One Way template does not create a callback port in the WSDL and callback invoke in the BPEL process. If you want to call an Asynchronous service and want to do something with an asynchronous callback, you should first use an ‘Invoke’ activity to call the service and then wait with a ‘Receive’ activity for the callback. Read the complete article here.
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