dmn-engine-java-main-method

Camunda Dmn Engine in a Java Main Method

This example demonstrates how to use the Camunda DMN engine as library in a custom application. The DMN Engine is added to the example as a Maven dependency. The example contains a Java class with a Main Method in which the DMN Engine is bootstraped and used to execute a decision table loaded from the classpath.

The used DMN Decision Table

The example uses a decision table from the DMN tutorial to decided which dish should be served to our guests for dinner:

You can find the corresponding DMN XML file dish-decision.dmn11.xml in the resources. To modify it you can use the Camunda Modeler.

Code Walkthrough

Maven Dependencies

Include the DMN engine BOM for dependency management:

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

Add the DMN engine as a dependency:

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

Include some slf4j backend. The simplest option is to not add a backend at all but simply redirect logging to jdk logging:

<!-- redirect slf4j logging to jdk logging -->
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-jdk14</artifactId>
  <version>1.7.26</version>
</dependency>

Bootstrap the DMN Engine in a Main Method

The Java Class DishDecider.java has a main method which bootstraps the DMN Engine using the default configuration:

public class DishDecider {

  public static void main(String[] args) {

    // create a new default DMN engine
    DmnEngine dmnEngine = DmnEngineConfiguration
      .createDefaultDmnEngineConfiguration()
      .buildEngine();

  }

}

Parsing and Executing the Decision Table

Once the DMN Engine is bootstrapped, it can be used to first parse a decision loaded from the classpath:

InputStream inputStream = DishDecider.class.getResourceAsStream("dish-decision.dmn11.xml");

DmnDecision decision = dmnEngine.parseDecision("decision", inputStream);

The parsed DmnDecsion can be cached and executed multiple times.

In order to execute it, it needs to be passed to the evaluateDecisionTable method:

DmnDecisionTableResult result = dmnEngine.evaluateDecisionTable(decision, variables);

The File DishDecider.java contains the complete source code including variable handling and parsing of the command line arguments.

Writing Tests with JUnit

Note: You can read more about decision testing in our User Guide.

DishDecisionTest.java uses the DmnEngineRule JUnit Rule to create a default DMN engine and than test different inputs on the decision:

public class DishDecisionTest {

  @Rule
  public DmnEngineRule dmnEngineRule = new DmnEngineRule();

  public DmnEngine dmnEngine;
  public DmnDecision decision;

  @Before
  public void parseDecision() {
    InputStream inputStream = DishDecisionTest.class.getResourceAsStream("dish-decision.dmn11.xml");
    dmnEngine = dmnEngineRule.getDmnEngine();
    decision = dmnEngine.parseDecision("decision", inputStream);
  }

  @Test
  public void shouldServeDryAgedInSpringForFewGuests() {
    VariableMap variables = Variables
      .putValue("season", "Spring")
      .putValue("guestCount", 4);

    DmnDecisionTableResult result = dmnEngine.evaluateDecisionTable(decision, variables);
    assertEquals("Dry Aged Gourmet Steak", result.getSingleResult().getSingleEntry());
  }

  @Test
  public void shouldServeSteakInSpringForSomeGuests() {
    VariableMap variables = Variables
      .putValue("season", "Spring")
      .putValue("guestCount", 7);

    DmnDecisionTableResult result = dmnEngine.evaluateDecisionTable(decision, variables);
    assertEquals("Steak", result.getSingleResult().getSingleEntry());
  }

  @Test
  public void shouldServeStewInSpringForMayGuests() {
    VariableMap variables = Variables
      .putValue("season", "Spring")
      .putValue("guestCount", 20);

    DmnDecisionTableResult result = dmnEngine.evaluateDecisionTable(decision, variables);
    assertEquals("Stew", result.getSingleResult().getSingleEntry());
  }

}

Running the Example

The example expects two arguments. First, the current season of the year and second the number of expected guests.

To run it you can either use maven:

mvn compile exec:java

This will compile the project and execute it with the arguments Winter for the current season and 4 for the number of expected guests.

This should produce an output which contains:

Dish Decision:
        I would recommend to serve: Roastbeef

You can specify other arguments with maven. For example for your summer party:

mvn compile exec:java -Dexec.args="Summer 32"

You can also create a executable Java jar file with:

mvn clean package

This will produce a DishDecider.jar file in the target folder. You can than call it like any other jar file:

java -jar target/DishDecider.jar Spring 6

Dish Decision:
        I would recommend to serve: Steak