Exercise: Implementing Resilience in a Java Spring Application

In this exercise, you will learn how to implement resilience in SAP Cloud SDK application. We will use the Mock Server to simulate the Business Partners service of SAP S/4HANA Cloud, public edition.

1. Enable resilience in the application you created in the previous exercise.

   1. Checkout the javaspring_v2.0_resilience Git branch by running the following commands in the terminal:

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      cd ~/projects/cloud-sdk-learning-journey
      git checkout -f javaspring_v2.1_resilience

      

2. Build and run the project.

   1. Build the application by running the following commands in the terminal

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      cd bpstandardvdm
      mvn clean install -Dmaven.test.skip=true

   2. Run the application by running the following commands in the terminal

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      cd application
      mvn spring-boot:run

      Note

      As an alternative, to run the application, you can open the Application.java file. Choose Run → Start Debugging or press F5.

      

3. Make sure that the Mock Server is up and running as described in the related previous exercise.

   1. In case the Mock server is installed but not started, you need to open a new terminal window and run the following commands:

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      cd ~/projects/cloud-s4-sdk-book
      npm run start

4. Query the Business Partner API of the Mock Server

   1. Open the requests.http file

   2. Click on Send Request in the requests.http file to submit the GET request for business partners

   3. Verify that the list of business partners are returned from the Mock Server. Note: If the Mock Server is not running, make sure to run the Mock Server on port 8081 by following the prerequisites at the top

      

   4. Stop the Mock Server by pressing Ctrl + C in the Mock Server project terminal

   5. Click on Send Request in the requests.http file to submit the GET request for business partners

   6. Verify that an empty list of business partners is returned due to resilience configuration

      

   7. Re-start the mock server and re-run the query to make sure it works again.

   8. Stop the running application using Ctrl + C in the corresponding terminal window.

   9. Note

      If you are not sure how to stop the mock server, you can run the following command from a new terminal window.

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      lsof -i:8081
      kill <node PID>

      

5. Optional: code walk-through.

   1. Review code in the following source files:

      File name	Comments on code changes
      BusinessPartnerController.java	Code logic is as follows... Annotate the method getBusinessPartners with @RequestMapping to handle the GET method Create a variable named destination of type HttpDestination with information about the Mock Server or API Business Hub Create a new instance of the utility class GetBusinessPartnersCommand and pass the destination as the constructor argument Call the execute method of the newly created instance to retrieve the list of Business Partners Return the list of business partners as part of the GET request
      GetBusinessPartnersCommand.java	Code logic is as follows... The constructor takes the destination as one of the arguments. It then calls the overloaded constructor passing the destination and an instance of the DefaultBusinessPartnerService class An instance of ResilienceConfiguration of type BusinessPartnerSrvice is created. SAP Cloud SDK comes with a default resilience configuration In our example, isolation mode is set to optional tenant + user, the bulkhead maximum concurrent calls is set to 20 and the execution timeout is set to 10000 milliseconds The executeSupplier method of ResilienceDecorator supports an optional 3rd parameter as a fallback function. In our example, a lambda function that returns an empty list is used
      requests.http	Provides various HTTP requests that can be submitted to query the Business Partner API
      commands.txt	Provides various commands that can be run on the terminal

      Note

      Review the exercise on SAP Tutorial Navigator on Introducing resilience to your application. https://developers.sap.com/tutorials/s4sdk-resilience.html