Implement a BPMN Event-based Gateway in Camunda

in Camunda on Camunda, Spring boot, Bpmn, Event-based gateway
Implement a BPMN Event-based Gateway in Camunda

The article contains a step-by-step guide on how to implement a BPMN Event-based Gateway in Camunda making use of a Spring Boot Application.

The article contains a step-by-step guide on how to implement a BPMN Event-based Gateway in Camunda making use of a Spring Boot Application. Camunda BPM is an open-source workflow and decision automation platform.

What is an Event-based Gateway

“The Event-Based Gateway represents a branching point in the Process where the alternative paths that follow the Gateway are based on Events that occur, rather than the evaluation of Expressions using Process data. A specific Event, usually the receipt of a Message, determines the path that will be taken. Basically, the decision is made by another Participant, based on data that is not visible to Process, thus, requiring the use of the Event-Based Gateway.” ~ BPMN Event-based Gateway

Getting Started Guide

The following is a step-by-step guide on how to implement a BPMN Event-based Gateway in Camunda making use of a Spring Boot Application.

Step 1: Create a Spring Boot Application

Create a spring boot application containing the Camunda BPM Engine. Use the Camunda BPM Initializr website to assist you in generating a Spring Boot application. Open the following URL in a browser and complete the form to bootstrap your application.

Fore a more detailed approach on how to create a spring boot application containing the Camunda BPM Engine, use the following link:

Step 2: Model the Process

Use Camunda Modeller to model the process. The process model is composed of four tasks, an event-based gateway, timer event and two message events:

BPMN Event-based Gateway Example of an event-based gateway

  • Submit Payment Request: Is a Service Task linked to a Delegate Expressions with the name ${logger}.
  • Payment Event: Is an Event-based Gateway with three sequence flows.
  • 2 min Timeout: Is a Timer Event with a duration of PT1M.
  • Payment Failed: Is a Message Event with a message name of payment-failed-message.
  • Payment Successful: Is a Message Event with a message name of payment-successful-message.
  • Submit Timeout Reversal: Is a Service Task linked to a Delegate Expressions with the name ${logger}.
  • Print Payment Failure Receipt: Is a Service Task linked to a Delegate Expressions with the name ${logger}.
  • Print Payment Receipt: Is a Service Task linked to a Delegate Expressions with the name ${logger}.

Step 3: Create a Java Delegate

Implement the org.camunda.bpm.engine.delegate.JavaDelegate interface:

@Component("logger")
public class ConsoleLoggerDelegate implements JavaDelegate {

    private final Logger LOGGER = LoggerFactory.getLogger(ConsoleLoggerDelegate.class.getName());

    public void execute(DelegateExecution execution) throws Exception {
        LOGGER.info("Place Order Process: " + execution.getCurrentActivityName());
    }
}

Step 4: Reference the JavaDelegate from BPMN

The JavaDelegate can be referenced using the delegateExpression attribute from the process Engine namespace:

<bpmn:serviceTask id="submit-payment-request" name="Submit Payment Request" camunda:delegateExpression="${logger}">
...
<bpmn:serviceTask id="submit-timeout-reversal" name="Submit Timeout Reversal" camunda:delegateExpression="${logger}">
...
<bpmn:serviceTask id="print-payment-failure-receipt" name="Print Payment Failure Receipt" camunda:delegateExpression="${logger}">
...
<bpmn:serviceTask id="print-payment-receipt" name="Print Payment Receipt" camunda:delegateExpression="${logger}">
...

Configure the service task using the properties panel wihtin the Camunda Modeler.

Camunda Modeller Camunda Modeller: Service Task Properties

Step 5: View the Spring Boot Application class

The Spring Boot application is implemented by a class called BasicEventBasedGatewayApplication. The class contains the @SpringBootApplication annotation that enables the spring boot auto configuration mechanism, enables the component scan on the packages and allow to register extra beans in the context.

@SpringBootApplication
public class BasicEventBasedGatewayApplication {
  public static void main(String[] args) {
    SpringApplication.run(BasicEventBasedGatewayApplication.class);
  }
}

Step 6: Configure the Camunda Spring Boot Application

The properties and configuration of the Spring Boot Application can be found in the application.yaml file within the src/main/resources folder. To startup your Camunda BPM Spring Boot application, you need to set some properties to allows you access.

The properties to configure your admin-user are listed below:

spring.datasource.url: jdbc:h2:mem:camunda-h2-database;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE

camunda.bpm.admin-user:
id: demo
password: demo

spring.h2.console:
enabled: true
path: /h2-console

Compile & Run The Example

1. Compile the application

Use the following command to compile the Spring Boot application making use of maven:

$ mvn clean install

2. Run the application

After you have successfully built the Camunda BPM Spring Boot application, the compiled artifact can be found in the target directory. Use the following command to start the Camunda BPM Spring Boot Application.

$ mvn spring-boot:run

3. Execute the example

After the application has started, run the following command in another terminal:

Run the command: Scenario 1 - Timeout

Scenario 1 is starting the Payment process and passing in the businesskey with a value of business-key-123. The event-based gateway waits for either the timer event to occur, or one of the two message events.

After two minutes the timer event is triggered and the payment is reversed.

$ ./start_process_scenario_01.sh

The script performs the following commands:

$ curl --location --request POST 'http://localhost:8080/engine-rest/process-definition/key/payment-process/start' --header 'Content-Type: application/json' --data-raw '{
       "businessKey": "business-key-123"
  }'

The following is the output to the console after running the above command.

Console Log Statements on Console

Run the command: Scenario 2 - Payment Failed

Scenario 2 is starting the Payment process and passing in the businesskey with a value of business-key-123. The event-based gateway waits for either the timer event to occur, or one of the two message events.

A payment-failed-message message is sent to the process instance with businesskey of value business-key-123 to indicate the payment has failed.

$ ./start_process_scenario_02.sh

The script performs the following commands:

$ curl --location --request POST 'http://localhost:8080/engine-rest/process-definition/key/payment-process/start' --header 'Content-Type: application/json' --data-raw '{
     "businessKey": "business-key-123"
}'

sleep 5

$ curl --location --request POST 'http://localhost:8080/engine-rest/message' --header 'Content-Type: application/json' --data-raw '{
     "messageName": "payment-failed-message",
     "businessKey": "business-key-123"
}'

The following is the output to the console after running the above command.

Console Log Statements on Console

Run the command: Scenario 3 - Payment Successful

Scenario 2 is starting the Payment process and passing in the businesskey with a value of business-key-123. The event-based gateway waits for either the timer event to occur, or one of the two message events.

A payment-successful-message message is sent to the process instance with businesskey of value business-key-123 to indicate the payment was successful.

$ ./start_process_scenario_03.sh

The script performs the following commands:

$ curl --location --request POST 'http://localhost:8080/engine-rest/process-definition/key/payment-process/start' --header 'Content-Type: application/json' --data-raw '{
     "businessKey": "business-key-123"
}'

sleep 5

$ curl --location --request POST 'http://localhost:8080/engine-rest/message' --header 'Content-Type: application/json' --data-raw '{
     "messageName": "payment-successful-message",
     "businessKey": "business-key-123"
}'

The following is the output to the console after running the above command.

Console Log Statements on Console

View Camunda Admin Console

To view the Camunda Admin Console, type the following url in your browser while the application is running. You will be prompted with the login screen.

After you have typed the above URL in a browser while the application is running, you will be prompted with the login screen. Type the Username and Password you set within the application properties file.

View the H2 Console

To view the H2 Console, type the following url in your browser while the application is running. You will be prompted with the login screen.

After you have typed the above URL in a browser while the application is running, you will be prompted with the login screen. Press the connect button since there is no password specified.

Example Code

The source code used in this example can be found on Github.

Finally

Congratulations !!! You have successfully implemented a BPMN Event-based Gateway in Camunda making use of a Spring Boot Application.