External Task Client Implementation in Camunda With Spring Boot Application

See how to use Spring Boot starter dependency to run the external task in Camunda.

Alok Singh

CORE ·

Jul. 27, 21 · Tutorial

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Today, we will be using Spring Boot starter dependency to run the external task in Camunda.

Create a Spring Boot project with the embedded Camunda Engine using this link. Use version 7.15.0.

Other Requirements:

Spring Boot 2.4.3
Camunda 7.15.0
Eclipse or any other IDE
Maven

Import the Maven project into Eclipse and add the below-mentioned files.

Add below additional dependency to the pom.xml file.

    XML
   
 

   <dependency>
  <groupId>org.camunda.bpm.springboot</groupId>
  <artifactId>camunda-bpm-spring-boot-starter-external-task-client</artifactId>
  <version>7.15.0</version>
</dependency>
  

Use Camunda modeler to save the below XML content with .bpmn extension to get the process model, which is having external service tasks as component.

    XML
   
 

   <?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:camunda="http://camunda.org/schema/1.0/bpmn" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" id="Definitions_1q1cbhv" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="3.4.1">
  <bpmn:process id="externalTaskClientProcess" name="External Task Client" isExecutable="true">
    <bpmn:startEvent id="StartEvent_1" name="Start">
      <bpmn:extensionElements>
        <camunda:executionListener event="start">
          <camunda:script scriptFormat="Groovy">println("process started")</camunda:script>
        </camunda:executionListener>
      </bpmn:extensionElements>
      <bpmn:outgoing>SequenceFlow_1hatjbw</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:sequenceFlow id="SequenceFlow_1hatjbw" sourceRef="StartEvent_1" targetRef="Task_08imlsr" />
    <bpmn:serviceTask id="Task_08imlsr" name="Get Interview Rating (1 to 10)" camunda:type="external" camunda:topic="ratingProvider">
      <bpmn:incoming>SequenceFlow_1hatjbw</bpmn:incoming>
      <bpmn:outgoing>SequenceFlow_1x5a8md</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:exclusiveGateway id="ExclusiveGateway_0hmq2sa">
      <bpmn:incoming>SequenceFlow_1x5a8md</bpmn:incoming>
      <bpmn:outgoing>SequenceFlow_08h0v2e</bpmn:outgoing>
      <bpmn:outgoing>SequenceFlow_0p8irmo</bpmn:outgoing>
    </bpmn:exclusiveGateway>
    <bpmn:sequenceFlow id="SequenceFlow_1x5a8md" sourceRef="Task_08imlsr" targetRef="ExclusiveGateway_0hmq2sa" />
    <bpmn:sequenceFlow id="SequenceFlow_08h0v2e" name="Rating > 6" sourceRef="ExclusiveGateway_0hmq2sa" targetRef="Task_1g5ymte">
      <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">${candidateScore > 6}</bpmn:conditionExpression>
    </bpmn:sequenceFlow>
    <bpmn:sequenceFlow id="SequenceFlow_0p8irmo" name="Rating <= 6" sourceRef="ExclusiveGateway_0hmq2sa" targetRef="Task_0f7ms7k">
      <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">${candidateScore <= 6}</bpmn:conditionExpression>
    </bpmn:sequenceFlow>
    <bpmn:exclusiveGateway id="ExclusiveGateway_0gfoi7x">
      <bpmn:incoming>SequenceFlow_05v92zi</bpmn:incoming>
      <bpmn:incoming>SequenceFlow_1g31asm</bpmn:incoming>
      <bpmn:outgoing>SequenceFlow_18vlx25</bpmn:outgoing>
    </bpmn:exclusiveGateway>
    <bpmn:sequenceFlow id="SequenceFlow_05v92zi" sourceRef="Task_0f7ms7k" targetRef="ExclusiveGateway_0gfoi7x" />
    <bpmn:endEvent id="EndEvent_01rktcj" name="End">
      <bpmn:incoming>SequenceFlow_18vlx25</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="SequenceFlow_18vlx25" sourceRef="ExclusiveGateway_0gfoi7x" targetRef="EndEvent_01rktcj" />
    <bpmn:sequenceFlow id="SequenceFlow_1g31asm" sourceRef="Task_1g5ymte" targetRef="ExclusiveGateway_0gfoi7x" />
    <bpmn:serviceTask id="Task_1g5ymte" name="Get Rating" camunda:type="external" camunda:topic="candidateRating">
      <bpmn:incoming>SequenceFlow_08h0v2e</bpmn:incoming>
      <bpmn:outgoing>SequenceFlow_1g31asm</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:scriptTask id="Task_0f7ms7k" name="Candidate Rejected" scriptFormat="Groovy">
      <bpmn:incoming>SequenceFlow_0p8irmo</bpmn:incoming>
      <bpmn:outgoing>SequenceFlow_05v92zi</bpmn:outgoing>
      <bpmn:script>println ("Candidate with score: " + candidateScore +" is rejected.");</bpmn:script>
    </bpmn:scriptTask>
    <bpmn:textAnnotation id="TextAnnotation_1qzfqxc">
      <bpmn:text>ratingProvider</bpmn:text>
    </bpmn:textAnnotation>
    <bpmn:association id="Association_0ce5iq8" sourceRef="Task_08imlsr" targetRef="TextAnnotation_1qzfqxc" />
    <bpmn:textAnnotation id="TextAnnotation_0vo2qx6">
      <bpmn:text>candidateRating</bpmn:text>
    </bpmn:textAnnotation>
    <bpmn:association id="Association_0y3fb6h" sourceRef="Task_1g5ymte" targetRef="TextAnnotation_0vo2qx6" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="externalTaskClientProcess">
      <bpmndi:BPMNShape id="_BPMNShape_StartEvent_2" bpmnElement="StartEvent_1">
        <dc:Bounds x="179" y="269" width="36" height="36" />
        <bpmndi:BPMNLabel>
          <dc:Bounds x="185" y="312" width="25" height="14" />
        </bpmndi:BPMNLabel>
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="SequenceFlow_1hatjbw_di" bpmnElement="SequenceFlow_1hatjbw">
        <di:waypoint x="215" y="287" />
        <di:waypoint x="270" y="287" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="ServiceTask_0ark1zc_di" bpmnElement="Task_08imlsr">
        <dc:Bounds x="270" y="247" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="ExclusiveGateway_0hmq2sa_di" bpmnElement="ExclusiveGateway_0hmq2sa" isMarkerVisible="true">
        <dc:Bounds x="425" y="262" width="50" height="50" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="SequenceFlow_1x5a8md_di" bpmnElement="SequenceFlow_1x5a8md">
        <di:waypoint x="370" y="287" />
        <di:waypoint x="425" y="287" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="SequenceFlow_08h0v2e_di" bpmnElement="SequenceFlow_08h0v2e">
        <di:waypoint x="450" y="262" />
        <di:waypoint x="450" y="200" />
        <di:waypoint x="550" y="200" />
        <bpmndi:BPMNLabel>
          <dc:Bounds x="454" y="183" width="51" height="14" />
        </bpmndi:BPMNLabel>
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="SequenceFlow_0p8irmo_di" bpmnElement="SequenceFlow_0p8irmo">
        <di:waypoint x="450" y="312" />
        <di:waypoint x="450" y="400" />
        <di:waypoint x="550" y="400" />
        <bpmndi:BPMNLabel>
          <dc:Bounds x="451" y="403" width="57" height="14" />
        </bpmndi:BPMNLabel>
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="ExclusiveGateway_0gfoi7x_di" bpmnElement="ExclusiveGateway_0gfoi7x" isMarkerVisible="true">
        <dc:Bounds x="715" y="262" width="50" height="50" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="SequenceFlow_05v92zi_di" bpmnElement="SequenceFlow_05v92zi">
        <di:waypoint x="650" y="400" />
        <di:waypoint x="740" y="400" />
        <di:waypoint x="740" y="312" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="EndEvent_01rktcj_di" bpmnElement="EndEvent_01rktcj">
        <dc:Bounds x="822" y="269" width="36" height="36" />
        <bpmndi:BPMNLabel>
          <dc:Bounds x="830" y="312" width="20" height="14" />
        </bpmndi:BPMNLabel>
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="SequenceFlow_18vlx25_di" bpmnElement="SequenceFlow_18vlx25">
        <di:waypoint x="765" y="287" />
        <di:waypoint x="822" y="287" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="SequenceFlow_1g31asm_di" bpmnElement="SequenceFlow_1g31asm">
        <di:waypoint x="650" y="200" />
        <di:waypoint x="740" y="200" />
        <di:waypoint x="740" y="262" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="ServiceTask_0ktpo8l_di" bpmnElement="Task_1g5ymte">
        <dc:Bounds x="550" y="160" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="ScriptTask_0jfnbcz_di" bpmnElement="Task_0f7ms7k">
        <dc:Bounds x="550" y="360" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="TextAnnotation_1qzfqxc_di" bpmnElement="TextAnnotation_1qzfqxc">
        <dc:Bounds x="370" y="160" width="100" height="30" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="Association_0ce5iq8_di" bpmnElement="Association_0ce5iq8">
        <di:waypoint x="356" y="247" />
        <di:waypoint x="407" y="190" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="TextAnnotation_0vo2qx6_di" bpmnElement="TextAnnotation_0vo2qx6">
        <dc:Bounds x="650" y="80" width="100" height="30" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="Association_0y3fb6h_di" bpmnElement="Association_0y3fb6h">
        <di:waypoint x="638" y="160" />
        <di:waypoint x="686" y="110" />
      </bpmndi:BPMNEdge>
    </bpmndi:BPMNPlane>
  </bpmndi:BPMNDiagram>
</bpmn:definitions>
  

If seen the saved content in diagram view in modeler, below is the diagram that should be there.

Add the below code snippet in application.yaml.

    YAML
   
 

   camunda.bpm.client:
  base-url: http://localhost:8080/engine-rest #URL of Process Engine
  lock-duration: 20000 # time in ms & external task will be locked
  subscriptions:
    ratingProvider: 
      variable-names: [] 
      process-definition-key: externalTaskClientProcess 
    candidateRating:
      variable-names: candidateScore
      process-definition-key: externalTaskClientProcess
  

Add the below external task implementations used in the process model namely ratingProvider and candidateRating.

    Java
   
 

   package com.example.workflow;

import java.util.logging.Level;
import java.util.logging.Logger;

import org.camunda.bpm.client.spring.annotation.ExternalTaskSubscription;
import org.camunda.bpm.client.task.ExternalTask;
import org.camunda.bpm.client.task.ExternalTaskHandler;
import org.camunda.bpm.client.task.ExternalTaskService;
import org.camunda.bpm.engine.variable.VariableMap;
import org.camunda.bpm.engine.variable.Variables;
import org.springframework.stereotype.Component;

@Component
@ExternalTaskSubscription("ratingProvider") 
public class GenerateRatingHandler implements ExternalTaskHandler {

	Logger logger = Logger.getLogger("GenerateRatingHandler");
	@Override
	public void execute(ExternalTask externalTask, ExternalTaskService externalTaskService) {
		
		String candidateId = "IN-" + (Math.random() * 100);
		int candidateScore = (int) (Math.random() * 11);

		VariableMap variables = Variables.createVariables();
		variables.put("candidateId", candidateId);
		variables.put("candidateScore", candidateScore);

		externalTaskService.complete(externalTask, variables); 

		logger.log(Level.INFO, "NOPE Rating Genrator External task is completed for Candidate {0} with rating {1}", new Object[]{candidateId, candidateScore});

	}

}

  

    Java
   
   package com.example.workflow;

import java.util.logging.Level;
import java.util.logging.Logger;

import org.camunda.bpm.client.spring.annotation.ExternalTaskSubscription;
import org.camunda.bpm.client.task.ExternalTask;
import org.camunda.bpm.client.task.ExternalTaskHandler;
import org.camunda.bpm.client.task.ExternalTaskService;
import org.springframework.stereotype.Component;

@Component
@ExternalTaskSubscription("candidateRating") 
public class CandidateRatingHanlder implements ExternalTaskHandler {

	Logger logger = Logger.getLogger("CandidateRatingHanlder");
	@Override
	public void execute(ExternalTask externalTask, ExternalTaskService externalTaskService) {
		
		 int candidateScore = externalTask.getVariable("candidateScore");

		  //Logic to process based on rating goes here
		 
		 externalTaskService.complete(externalTask);
		 
		 logger.log(Level.INFO, "Processing candidate Score received {0}", new Object[]{ candidateScore});

	}

}

Run the application using the main class file and observe the output where the external tasks implemented in the Spring Boot project will be getting executed.

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