Exercise 4 - Exclusive Gateways

Prerequisites | Exercise 1 | Exercise 1.1 | Exercise 2 | Exercise 3 | Exercise 4 | Exercise 5

Exercise 4 - Exclusive Gateways

Different execution paths in a process based on the state of process variables can be achieved using Exclusive Gateways. In Exercise 4 we will examine how this can be implemented by modifying the highmedorg_helloDic process.

Introduction

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Exclusive Gateways

Different sequence flows during the execution of a process instance can be modeled using BPMN Exclusive Gateways. For each outgoing sequence flow of the gateway, a BPMN Condition Expression can be added to the process model, deciding whether a sequence flow should be followed. Thereby, all condition decisions must be in an XOR relationship to each other.

Condition Expressions

A BPMN Condition Expression uses the ${..} notation. Within the curly braces all execution variables of a process instance can be accessed, e.g. the ones that were stored in a previous Java implementation of a BPMN ServiceTask. For example, the BPMN Condition Expression ${cohortSize > 100} checks whether the value in the execution variable cohortSize is greater than 100.

Storing / Modifying Process Variables

Via the DelegateExecution execution parameter of the doExecute method of a class extending AbstractServiceDelegate, we can write and read process variables of the current process instance. The following code listing show how to write and read a boolean variable:

{
	execution.setVariable("variable-name", Variables.booleanValue(false));
	boolean variable = (boolean) execution.getVariable("variable-name");
}

For more details on process variables see the Camunda documentation.

Exercise Tasks

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1. In the HelloDic class, write an algorithm deciding based on the "leading" Task's input parameter tutorial-input, whether the highmedorg_helloCos process should be started.
2. Add a boolean variable to the process instance execution variables storing the decision.
3. Add an exclusive gateway to the highmedorg_helloDic process model and two outgoing sequence flows - the first starting process highmedorg_helloDic, the second stopping process highmedorg_helloDic without starting process highmedorg_helloCos.
4. Add a condition expressions to each outgoing sequence flow based on the previously stored execution variable.

Solution Verification

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Maven Build and Automated Tests

Execute a maven build of the dsf-process-tutorial parent module via:

mvn clean install -Pexercise-4

Verify that the build was successful and no test failures occurred.

Process Execution and Manual Tests

To verify the highmedorg_helloDic and highmedorg_helloCos processes can be executed successfully, we need to deploy them into DSF instances and execute the highmedorg_helloDic process. The maven install build is configured to create a process jar file with all necessary resources and copy the jar to the appropriate locations of the docker test setup.

1. Start the DSF FHIR server for the Test_DIC organization in a console at location .../dsf-process-tutorial/test-setup:

docker-compose up dic-fhir

Verify the DSF FHIR server started successfully.

2. Start the DSF BPE server for the Test_DIC organization in a second console at location .../dsf-process-tutorial/test-setup:

docker-compose up cos-fhir

Verify the DSF FHIR server started successfully.

3. Start the DSF BPE server for the Test_COS organization in a fourth console at location .../dsf-process-tutorial/test-setup:

docker-compose up cos-bpe

Verify the DSF BPE server started successfully and deployed the highmedorg_helloCos process.

4. Start the highmedorg_helloDic process by posting a specific FHIR Task resource to the DSF FHIR server of the Test_DIC organization: Execute therefore the main method of the org.highmed.dsf.process.tutorial.TutorialExampleStarter class to create the Task resource needed to start the highmedorg_helloDic process.

Verify that the highmedorg_helloDic process was executed successfully by the Test_DIC DSF BPE server and possibly the highmedorg_helloCos process by the Test_COS DSF BPE server, depending on whether decision of your algorithm based on the input parameter allowed to start the highmedorg_helloDic process.

Continue with exercise 5

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Prerequisites | Exercise 1 | Exercise 1.1 | Exercise 2 | Exercise 3 | Exercise 4 | Exercise 5