Exposing Several Services as a Single Service

In the ESB profile of WSO2 Enterprise Integrator (WSO2 EI), this is commonly referred to as Service Chaining, where several services are integrated based on some business logic and exposed as a single, aggregated service. 

Let's get started!

Connecting to the back-end services

Let's create HTTP endpoints to the back-end services that you need to connect, in order to check the channeling fee and to settle payment.

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:

   Click Finish.

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3. Create another endpoint for Settle Payment and fill in the information as in the following table: 

   Click Finish.

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You have now created the additional endpoints that are required for this tutorial. 

Creating the deployable artifacts

1. In EI Tooling, add a Property mediator just after the Get Hospital Property mediator in the In sequence of the API resource to retrieve and store the card number that is sent in the request payload.

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   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

2. Go to the first case box of the Switch mediator. Add a Property mediator just after the Log mediator to store the value for uri.var.hospital variable that will be used when sending requests to ChannelingFeeEP.
   

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   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

3. Similarly, add property mediators in the other two case boxes in the Switch mediator. Change only the Value field as follows:

   • Case 2: clemency

   • Case 3: pinevalley
     

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4. Delete the Send mediator by right clicking on the mediator and selecting Delete from Model. Replace this with a Call mediator from the Mediators palette and add GrandOakEP from the Defined Endpoints palette to the empty box adjoining the Call mediator. 
   
   Replace the Send mediators in the following two case boxes as well and add ClemencyEP and PineValleyEP to the respective boxes adjoining the Call mediators.
   

   Let's use Property mediators to retrieve and store the values that you get from the response you receive from GrandOakEP, ClemencyEP or PineValleyEP.

5. Next to the Call mediator box, add a Property mediator to retrieve and store the value sent as appointmentNumber.

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   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

6. Similarly, add two more Property mediators as follows. They retrieve and store the doctor details and patient details respectively, from the response that is received from GrandOakEP, ClemencyEP or PineValleyEP.

   
   
   

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7. Add a Call mediator and add ChannelingFeeEP from Defined Endpoints palette to the empty box adjoining the Call mediator. 

8. Add a Property mediator adjoining the Call mediator box to retrieve and store the value sent as actualFee. Access the Property tab of the mediator and fill in the information as in the following table:

   Let's use the PayloadFactory mediator to construct the following message payload for the request sent to SettlePaymentEP. 

   {"appointmentNumber":2, "doctor":{ "name":"thomas collins", "hospital":"grand oak community hospital", "category":"surgery", "availability":"9.00 a.m - 11.00 a.m", "Fee":7000.0 }, "patient":{ "name":"John Doe", "Dob":"1990-03-19", "ssn":"234-23-525", "address":"California", "phone":"8770586755", "email":"johndoe@gmail.com" }, "fee":7000.0, "confirmed":false, "card_number":"1234567890" }

9. Next to the Property mediator, add a PayloadFactory mediator from the mediators palette to construct the above message payload. 

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   With the Payloadfactory mediator selected, access the properties tab of the mediator and fill in the information as in the following table:

   We will look at adding the value for the field Args in the following steps.

10. To add the Args field for the PayloadFactory mediator, click the Browse (...) icon in the Args field. Click on the Add button and enter the following information as in the table below. It provides the argument that defines the actual value of the first variable used in the format definition in the previous step.

11. Similarly, click Add and add more arguments to define the other variables that are used in the message payload format definition. Use the following as the Value for each of them: 

    $ctx:doctor_details
$ctx:patient_details
$ctx:actual_fee
$ctx:card_number
    

12. Add a Call mediator and add SettlePaymentEP from Defined Endpoints palette to the empty box adjoining the Call mediator.

13. Add a Respond mediator to send the response to the client. 
    
    You should now have a completed configuration that looks like this:
    

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14. Save the updated REST API configuration.