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 instead of the actual SAP S/4HANA Cloud.

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

   1. Checkout the initial Git branch javaspring_v2.0_resilience. To do this, open a Terminal and run the following commands, make sure current working directory is /home/user/projects/cloud-sdk-learning-journey.:

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      cd ~/projects/cloud-sdk-learning-journey
      git checkout -f javaspring_v2.0_resilience

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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

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   2. Open the Application.java file. Press F5 to run the application

      

3. Query the Business Partner API of SAP S/4HANA Cloud

   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

      

4. Optional: Review code in the following source files

   1. Note

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

      Code walk-through

      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

5. Optional: Manually create the project. The following steps create an exact replica of the project you just checked out using Git.

   Note

   Before you execute this step, you must execute the corresponding optional step, described in the previous Querying SAP APIs in a Java Spring application exercise.

   1. Create or update the following files in the table below

      File name	Type	Contents
      BusinessPartnerController.java Path: ~/projects/bpstandardvdm/application/src/main/java/com/sap/cloud/sdk/tutorial/controllers	Modified	Copy contents from here...
      GetBusinessPartnersCommand.java Path: ~/projects/bpstandardvdm/application/src/main/java/com/sap/cloud/sdk/tutorial/utils	New	Copy contents from here...

      

   2. Build and run the project in projects/bpstandardvdm in the same exact way you did in the previous steps with project in projects/cloud-sdk-learning-journey/bpstandardvdm.