dmn-engine-drg

Decision Requirements Graph (DRG) Example

This example demonstrates how to use the Camunda DMN engine as library in a custom application to evaluate a decision from a DRG. 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 loaded from the classpath.

The used Decision Requirements Graph

The example uses the DRG from the Reference Guide to decide which beverages should be served to our guests for dinner:

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You can find the corresponding DMN XML file dinnerDecisions.dmn in the resources.

Code Walkthrough

Refer dmn-engine-java-main-method example for Maven dependencies and bootstrapping the DMN Engine.

Parsing and Executing the Decision of the DRG

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

InputStream inputStream = BeveragesDecider.class.getResourceAsStream("dinnerDecisions.dmn");

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

The parsed DmnDecsion can be cached and executed multiple times.

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

DmnDecisionResult result = dmnEngine.evaluateDecision(decision, variables);

The File BeveragesDecider.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.

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

@Test
public void shouldServeGuiness() {

  VariableMap variables = Variables
    .putValue("season", "Spring")
    .putValue("guestCount", 10)
    .putValue("guestsWithChildren", false);

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

  assertThat(result.collectEntries("beverages"))
    .hasSize(2)
    .contains("Guiness", "Water");
}

Running the Example

The example expects three arguments. First, the current season, second the number of guests (integer) and third if guests has children (boolean).

To run it you can either use maven:

mvn compile exec:java

This will compile the project and execute it with the arguments Spring for the current season, 10 for the guest count and false for guests with children.

This should produce an output which contains:

Beverages:
	I would recommend to serve: [Guiness, Water]

You can specify other arguments with maven. For example:

mvn compile exec:java -Dexec.args="Winter 7 true"

You can also create a executable Java jar file with:

mvn clean package

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

java -jar target/BeveragesDecider.jar Spring 10 false

Beverages:
        I would recommend to serve: [Guniess, Water]