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REST Service Task

This quickstart demonstrates how to use the built-in REST HTTP connector for invoking REST services in Camunda Platform. The example is classless, relying entirely on scripting and expression language. It makes use of the camunda Connect and the camunda Spin extensions.

The example includes a BPMN 2.0 process which invokes a holiday service, parses the result and takes a decision based on the result:

REST Example Process

Overview

How to run it

  1. Checkout the project with Git
  2. Read and run the unit test

How it works

The important part of this example is the service task Get holiday. It uses the HTTP connector provided by camunda Connect and processes the returned JSON using camunda Spin. For reference, have a look at the complete BPMN XML.

Configuring Connect and Spin

Since Connect and Spin are optional extensions to the camunda platform, they have to be added as dependencies in pom.xml:

...
<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.camunda.bpm</groupId>
      <artifactId>camunda-bom</artifactId>
      <scope>import</scope>
      <type>pom</type>
      <version>${version.camunda}</version>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  ...
  <dependency>
    <groupId>org.camunda.bpm</groupId>
    <artifactId>camunda-engine-plugin-connect</artifactId>
  </dependency>

  <dependency>
    <groupId>org.camunda.connect</groupId>
    <artifactId>camunda-connect-http-client</artifactId>
  </dependency>

  <dependency>
    <groupId>org.camunda.bpm</groupId>
    <artifactId>camunda-engine-plugin-spin</artifactId>
  </dependency>

  <dependency>
    <groupId>org.camunda.spin</groupId>
    <artifactId>camunda-spin-dataformat-json-jackson</artifactId>
  </dependency>
  ...
</dependencies>
...

Note the dependencyManagement entry. It declares the camunda bill of material (BOM) that provides managed dependencies for all camunda artifacts. These are referenced in the dependencies section. The BOM ensures that the version of the dependencies are consistent with each other.

Next, the process engine plugins provided by Spin and Connect are registered with the engine in camunda.cfg.xml:

...
<beans ...>

  <bean id="processEngineConfiguration" class="org.camunda.bpm.engine.impl.cfg.StandaloneInMemProcessEngineConfiguration">

    ...
    <!-- activates the camunda Connect process engine plugins -->
    <property name="processEnginePlugins">
      <list>
        <bean class="org.camunda.connect.plugin.impl.ConnectProcessEnginePlugin" />
        <bean class="org.camunda.spin.plugin.impl.SpinProcessEnginePlugin" />
      </list>
    </property>

  </bean>
</beans>

This ensures that connectors can be used with service tasks and that the Spin functions are available from scripts and expressions.

Using a Connector Service Task for REST requests

The task Get holiday makes use of Connect's HTTP connector. It does the following things:

  1. Invoke a REST web service using the HTTP connector provided by camunda Connect.
  2. Extract a property indicating whether a day is a holiday from the service's JSON response using Javascript and camunda Spin. This variable is used on the follow-up exclusive gateway.

In general, the task is declared as follows (see the process model):

<bpmn2:serviceTask id="ServiceTask_1" name="Get holiday">
  <bpmn2:extensionElements>
    <camunda:connector>
      CONNECTOR DECLARATION
    </camunda:connector>
  </bpmn2:extensionElements>
  <bpmn2:incoming>SequenceFlow_1</bpmn2:incoming>
  <bpmn2:outgoing>SequenceFlow_2</bpmn2:outgoing>
</bpmn2:serviceTask>

The task uses a camunda:connector extension element. It means that a connector should be invoked when the service task is executed. In detail, the connector is declared as follows:

<camunda:connector>
  <camunda:connectorId>http-connector</camunda:connectorId>
  <camunda:inputOutput>

    <camunda:inputParameter name="url">
      http://feiertage.jarmedia.de/api/?jahr=2014&amp;nur_land=BE
    </camunda:inputParameter>

    <camunda:inputParameter name="method">
      GET
    </camunda:inputParameter>

    <camunda:inputParameter name="headers">
      <map>
        <entry key="Accept">
          application/json
        </entry>
      </map>
    </camunda:inputParameter>

    <camunda:outputParameter name="isHoliday">
      <camunda:script scriptFormat="Javascript" resource="parseHoliday.js" />
    </camunda:outputParameter>
  </camunda:inputOutput>
</camunda:connector>

The connector-id element identifies the HTTP connector. The inputOutput element defines a mapping of values to connector parameters. For example, the url parameter identifies the REST endpoint to be called.

The outputParameter element maps the response obtained by the connector to a variable isHoliday. The mapping makes use of camunda Spin to extract an element from the returned JSON and is implemented in a Javascript file.