Routing Requests Based on Message Content

The message payload sent by the client to WSO2 ESB for making an appointment reservation will contain the hospital name where the appointment needs to be confirmed. The HTTP request method used will be POST. Based on the hospital name sent in the request message, WSO2 ESB will then route the appointment reservation to the relevant hospital's backend service.

For more details on how routing of messages within WSO2 ESB is done based on the message content, refer to  Content-Based Router Enterprise Integration Pattern.  

Let's get started!

This tutorial contains the following sections:

Let's now create three different HTTP endpoints for the above services.

1. Right-click SampleServices in the Project Explorer and navigate to New -> Endpoint. Ensure Create a New Endpoint is selected and click Next.

2. Fill in the information as in the following table:

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   Click Finish.

3. Create similar HTTP endpoints for the other two hospital services using the relevant URI Template as follows:

   • ClemencyEP :   http://wso2training-restsamples.wso2apps.com/clemency/categories/{uri.var.category}/reserve

   • PineValleyEP :   http://wso2training-restsamples.wso2apps.com/pinevalley/categories/{uri.var.category}/reserve

You have now created three endpoints for the three hospital backend services that will be used to make appointment reservations.

To implement the routing scenario, we will update the REST API we created in the previous section by adding a new API resource. We will then use a Switch mediator to route the message to the relevant backend service based on the hospital name passed in the payload of the request message. 

Let’s update the REST API we created in the previous tutorial using WSO2 ESB Tooling.

1. In the REST API configuration, select API Resource in the API palette and drag it onto the canvas just below the previous API resource that was created.
   

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2. With the API Resourceyou added in the previous step selected, access the Properties tab and fill in the following details:
   
   

   • Url Style: Click in the Value field, click the down arrow, and then select URI_TEMPLATE from the list

   • URI-Template: /categories/{category}/reserve

3. Set the value of Post to true in the Methods section of the properties tab.

4. Drag a Property Mediator from the Mediators palette to the In Sequence of the API resource and name it Get Hospital. This will be used to extract the hospital name that is sent in the request payload.

5. With the Property mediator selected, access the Properties tab and fill in the following details:

   • Property Name: New Property...

   • New Property Name: Hospital

   • Property Action: set

   • Value Type: Expression

6. We will now add the JSONPath expression that will extract the hospital from the request payload. Click value field of Value Expression in the Properties tab and add the following expression:
   json-eval($.hospital)

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7. Add a Switch mediator from the Mediator palette just after the Property Mediator you added above. 

8. Right-click the Switch mediator you just added and select Add/Remove Case to add the number of cases you want to specify. In this scenario, we are assuming there are three different hospitals, hence there are there are three cases. Enter 3  for Number of branches and click OK. 
   

   
   
   

9. With the Switch mediator selected, go to the Properties tab.

10. The Source XPath field is where we will specify the XPath expression that obtains the value of Hospital that we stored in the Property mediator. To specify the expression, click in the Value field of the Source XPath property, click the browse (...) button, and then overwrite the default expression with the following and click OK:

    get-property('Hospital') 
    

11. Click in the Value field of the Case Branches property, click the browse (...) button, and then change the RegExp value as follows:

    • Case 1: grand oak community hospital

    • Case 2:  clemency medical center

    • Case 3:  pine valley community hospital

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    Click OK. 

12. Let's add a Log mediator to print a message indicating to which hospital the request message is being routed. Drag a Log mediator to the first Case box of the Switch mediator, name it 'Grand Oak Log', access the Properties tab and enter the following:

    • Log Category: INFO

    • Log Level: CUSTOM

13. Click the Value field of the Properties property, and then click the browse (...) icon that appears. In the Log Mediator Configuration dialog box, click New, and then add a property called 'message' as follows:

    • Name: message

    • Type: EXPRESSION
      We select EXPRESSION because the required properties for the log message must be extracted from the request, which we can do using an XPath expression.

    • Value/Expression: Click the browse (...) icon in the Value/Expression field and enter the following:

      • Property expression: fn:concat('Routing to ', get-property('Hospital'))
        This is an XPath expression value that uses the value stored in the Property mediator and will then concatenate the two strings to display the log message “Routing to <hospital name>”.

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    Click OK.

14. Add a Send mediator adjoining the Log mediator and add GrandOakEP from Defined Endpoints palette to the empty box adjoining the Send mediator.
    

15. Add Log mediators in the other two Case boxes in Switch mediator and then enter the same properties as in Step 13. Name the two Log mediators as 'Clemency Log' and 'Pine Valley Log'. 
    Add Send mediators adjoining these log mediators and respectively add endpoints ClemencyEP and PineValleyEP from the Defined Endpoints palette.

    You have now configured the Switch mediator so that when a request is sent to this API resource,  the message "Routing to <Hospital Name>" will be logged. The request message will then we routed to the relevant hospital backend service based on the hospital that is sent in the request payload. 

16. Let's now configure the default case in the switch mediator. This will handle requests where an invalid hospital is sent in the request payload.  Add a Log mediator to the Default (the bottom box) of the Switch mediator and configure it the same way you did for the Log mediator above, this time naming it Fault Log and changing its Value/Expression as follows:
    fn:concat('Invalid hospital - ', get-property('Hospital'))
    This results in the message "Invalid hospital - <Hospital Name>" to be logged for requests where the request payload contains an invalid hospital.

17. Drag a Respond mediator adjoining the Log mediator you added in the above step. This ensures that there is no further processing of the current message and returns the request message back to the client.
    
    The API resource configuration should now look like this:
    

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18. Drag a Send mediator to the Outsequeneofthe API resource to send the response back to the client. 

19. Save the updated REST API configuration.