Converting Synchrous BPEL process to Asynchronous BPEL process

This article is about how to convert a synchronous BPEL process to an asynchronous one.

Whenever we create new bpel process three files are created by default viz.

• [processName].bpel
• [processName].wsdl
• bpel.xml

But the difference between the Synchronous and Asynchronous process remains in the .bpel and .wsdl files only.

If we open the .bpel and .wsdl file of both the processes we do not find much difference in the two therefore it's very easy to convert an asynchronous process to synchronous one and vice-versa.

For explaining how to convert the synchronous process to asynchronous one I have created a BPEL process SynchBP. I’ll be converting SynchBP which is a Synchronous BPEL process to an asynchronous one. As earlier said the difference is only in .bpel and .wsdl file so we'll concentrate only on these two files.

For ease of understanding I have used colours in the text so as to highlight what to change and what to add.

So, first start with SynchBP.bpel file.

There are three places where we have to make changes viz. partnerlink, receive, and reply element.

Partnerlink:

This is how the partnerlink element is of a SynchBP:

<partnerLink name="client" partnerLinkType="client:SynchBP" myRole="SynchBPProvider"/>

Add another attribute partnerRole="SynchBPRequester" to this element. The partnerlink will look like this:

<partnerLink name="client" partnerLinkType="client:SynchBP" myRole="SynchBPProvider" partnerRole="SynchBPRequester"/>

Receive Element:

Below is the receive element of SynchBP

<receive name="receiveInput" partnerLink="client" portType="client:SynchBP" operation="process" variable="inputVariable"

createInstance="yes"/>

Change the value of attribute operation from process to initiate. The partnerlink will look like this:

<receive name="receiveInput" partnerLink="client" portType="client:SynchBP" operation="initiate" variable="inputVariable" createInstance="yes"/>

Reply element:

Below is the reply element of SynchBP

<reply name="replyOutput" partnerLink="client" portType="client:SynchBP" operation="process" variable="outputVariable"/>

Do the following changes to make it for asynchronous process:

• Change the element name from reply to invoke.
• Change the name attribute value from replyOutput to callbackClient.
• Change the value of attribute portType from client:SynchBP to client:SynchBPCallback (or simply [processName]Callback ).
• Change operation=”process” to operation=”onResult”.
• Change the name of last attribute i.e. variable to inputvariable.

<invoke name="callbackClient" partnerLink="client" portType="client:SynchBPCallback" operation="onResult" inputVariable="outputVariable"/>

Here we are done with SynchBP.bpel, now we need to edit SynchBP.wsdl.

There are very few changes to be made in the .wsdl file.

The elements that need to be changed are portType and partnerLinkType.

portType:

This is how a portType is defined in a synchronous process:

<portType name="SynchBP">

<operation name="process">

<input message="client:SynchBPRequestMessage" />

<output message="client:SynchBPResponseMessage"/>

</operation>

</portType>

Create another portType element with name SynchronousProcessCallback and operation as onResult. Now delete the output element from both portTypes and in the SynchronousProcessCallback portType, change the attribute value from client:SynchBPRequestMessage to client:SynchBPResponseMessage. (Help: Copy & paste the already defined portType and do as below)

<portType name="SynchBP">

<operation name="initiate">

<input message="client:SynchBPRequestMessage" />

<output message="client:SynchBPResponseMessage"/> ……Remove this

</operation>

</portType>

<portType name="SynchBPCallback">

<operation name="onResult">

<input message="client:SynchBPRequestMessage"/>……. Remove this

<input message="client:SynchBPResponseMessage"/>

</operation>

</portType>

partnerLinkType:

This is how partnerlink information is provided in a wsdl of a synchronous process:

<plnk:partnerLinkType name="SynchBP">

<plnk:role name="SynchBPProvider">

<plnk:portType name="client:SynchBP"/>

</plnk:role>

</plnk:partnerLinkType>

Inside partnerLinkType create one more role element and give it a name as SynchronousProcessRequester. Now inside the role element for portType element change the value of name attribute to client:SynchronousProcessCallback.

<plnk:partnerLinkType name="SynchBP">

<plnk:role name="SynchBPProvider">

<plnk:portType name="client:SynchBP"/>

</plnk:role>

<plnk:role name="SynchBPRequester">

<plnk:portType name="client:SynchBPCallback"/>

</plnk:role>

</plnk:partnerLinkType>

Here we are done with .wsdl file and the SynchBP process is now an asynchronous BPEL Process.

Asynchronous vs. Synchronous BPEL process

This article explains the difference between an asynchronous and a synchronous process.

I have tried to explain the difference with the help of a simple example below:

Suppose there are two processes SynchronousBPELProcess and AsynchronousBPELProcess. As the name suggest former one is a synchronous and later one is an asynchronous BPEL process. Also there is a third process which we’ll call as Client. The Client invokes the above processes.

Case 1: Client invokes SynchronousBPELProcess.

1. Client invokes SynchronousBPELProcess.
2. SynchronousBPELProcess gets instantiated and starts its operations while Client waits for the response from the SynchronousBPELProcess.
3. SynchronousBPELProcess completes its operations and sends a response back to Client.
4. Client continues and completes its processing.

Case 2: Client invokes AsynchronousBPELProcess

1. Client invokes AsynchronousBPELProcess.
2. AsynchronousBPELProcess gets instantiated and starts its operations while Client also continues to perform its operations.
3. AsynchronousBPELProcess completes its operations and callback the Client with the response message.

Here we noticed that if a synchronous process is invoked, the operations of this process has to be completed first and only then the client is able to resume its operations while in the case of asynchronous both the process continues to perform their operations.

Fig1: An image showing bpel diagram of an asynchronous and a synchronous process.

What makes the difference?

Synchronous Process:

The synchronous process defines one two way operation port to receive the request and send the response. Using the invoke activity the client invokes the Synchronous BPEL process on this port and waits to receive the response on the same port. As soon as the client receives the response from the BPEL process it continues with its flow. On the BPEL process side, the Synchronous BPEL process gets instantiated on receiving the client request and sends back the reply using the reply activity on the same port on which the Client is waiting.

Asynchronous Process:

In the asynchronous process two one way operations ports are defined to receive the request and send the response. On the client side, the client uses the invoke activity to invoke the asynchronous BPEL process and continues with its flow. It uses the receive activity to receive the response later in the flow. The asynchronous BPEL process receives the request on one of the ports and sends back the reply from another port (callback port). To send the response the asynchronous BPEL process invokes the client on the callback port using the callback activity.

Fig 2: An image showing the wsdl of an asynchronous and a synchronous process.

Fig 3: An image showing a call to asynchronous and synchronous process.

We also find different operation names like initiate, onResult and process in the .bpel file. These are just labels to differentiate between sync and async processes.

* A port is nothing but a method with input and output. So a two way operation port has an input and an output while a one way operation port has only input or output.