dmndemo

Sample Project showing Usage of camunda DMN engine working with DMN-compliant Decision Tables.

It uses SpringBoot as a basis and performs a Test on a predefined decision-Table (for modelling see the DMN Modeler ).

Howto

Just clone, mvn clean eclipse:eclipse and run the Test - e.g. in your IDE, to see what´s going on.

Call Java-Method from within DMN-Table to execute more complex logic

In some cases the build in Expression Language FEEL isn´t sufficient to check more complex Logic. In this case, it´s nice to simply call a Java-Method from within your Decision-Table via the Groovy Expression Language, which is supported in camunda´s DMN Expressions.

For that you need to add Groovy to your Classpath (I omit the version here, because SpringBoot ships Groovy already):

<dependency>
  <groupId>org.codehaus.groovy</groupId>
  <artifactId>groovy-all</artifactId>
</dependency>

In your Decisiontable you need to define a simple column with a name (in this example it´s "zip") you´ll use later when calling the DMN-Engine and a appropriate Datatype - e.g. String.

Then add your Custom-Logic within a Java-Class´ static method (that returns a boolean) to the Project, import the Class in Groovy and call the Method - e.g. like that:

import de.jonashackt.dmndemo.PostalcodeChecker
return PostalcodeChecker.isValidPostalcode(cellInput);

Note the correct import of your Class and also note the usage of "cellInput" - which contains the Value to check, passed into the DMN-Engine along with the other Variables.

A Note for users of DMN-Modeler: If you use the camunda DMN-Modeler (which is a good idea :) ): the last stable Version (0.3.x) removed the Script-Call at the moment - this didn´t happen with the current Nightly-Build any more.

You need to resist to use the camunda-Modeler feature to insert a "Script" into a table column:

This will execute the script all the time the decisiontable is evaluated.

As long as this feature isn´t shipped, there are 2 Options:

Option 1: You have to open the dmn.xml in a texteditor and alter a rule yourself - e.g. like this:

<inputEntry id="UnaryTests_0h6fb9j" expressionLanguage="Groovy">        <text><![CDATA[import de.jonashackt.dmndemo.PostalcodeChecker
return PostalcodeChecker.isValidPostalcode(cellInput);]]></text>
</inputEntry>

Option 2: You insert the groovy-Script via the camunda-Modeler and open the XML after saving it up, to add the expressionlanguage-Definition to the right rule:

 expressionLanguage="Groovy"

Now if you run a Test, which fill´s the VariableMap correctly, it should evaluate your Rule and call the Java-Method with your Custom logic:

// Should be ok
VariableMap variables = Variables
        .putValue("state", "France")
        .putValue("product", "RedCar")
        .putValue("zip", "99425");

DmnDecisionTableResult result = dmnEngine.evaluateDecisionTable(states2ship, variables);
assertNotNull(result.getSingleResult());
assertEquals("notok", result.getSingleResult().getEntryMap().get("result"));
assertEquals("sorry, no shipment possible", result.getSingleResult().getEntryMap().get("reason"));

To see all this in Action, simply run DmndemoApplicationTests.java.