# DMN: Create a custom function

**URL:** <https://forum.flowable.org/t/dmn-create-a-custom-function/7446>\
**Category:** Uncategorized\
**Created:** [February 3, 2021, 1:51pm UTC](https://forum.flowable.org/t/dmn-create-a-custom-function/7446 "2021-02-03T13:51:02Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![brunofigalveskk](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.flowable.org/brunofigalveskk/32/2230_2.png) [@brunofigalveskk](https://forum.flowable.org/u/brunofigalveskk)\
**Post date:** [February 3, 2021, 1:51pm UTC](https://forum.flowable.org/t/dmn-create-a-custom-function/7446/1 "2021-02-03T13:51:03Z")

</div>

Hi everyone,

I’m trying to find some help with custom functions for DMN engine. So, I’m using the flowable-spring-boot-starter-rest and I’m trying to execute a DMN rule with a custom function.

I created my custom function NextBusinessDay:

```
public class NextBusinessDay extends AbstractFlowableFunctionDelegate {

    public NextBusinessDay() {
    }

    @Override
    public String prefix() {
        return "dates";
    }

    @Override
    public String localName() {
        return "nextBusinessDay";
    }

    @Override
    public Class<?> functionClass() {
        return DateUtils.class;
    }

    @Override
    public Method functionMethod() {
        return getSingleObjectParameterMethod("nextBusinessDay");
    }
}

```

This is the static method that I aims to be called:

```
public class DateUtils {

    public static Date nextBusinessDay(Date d) {
        return org.apache.commons.lang3.time.DateUtils.addDays(d, 5);
    }

}

```

Here is my DMN engine setup where I have already deployed a DMN table and added my custom function NextBusinessDay.

```
@Configuration
public class DmnEngineSetup {
    @Autowired
    private DmnEngine engine;
    private URL url = getClass().getResource("/dmn");
    private List<FlowableFunctionDelegate> flowableFunctionDelegateList =
            Arrays.asList(new NextBusinessDay());

    @PostConstruct
    public void deploy() throws URISyntaxException, IOException {
        engine.getDmnEngineConfiguration()
                .setCustomFlowableFunctionDelegates(flowableFunctionDelegateList);

        Path path = Paths.get(url.toURI());
        Files.list(path).forEach(p -> {
            engine.getDmnRepositoryService()
                    .createDeployment()
                    .name("test")
                    .addClasspathResource("dmn/" + p.getFileName().toString())
                    .enableDuplicateFiltering()
                    .deploy();
        });
    }

}

```

Finally, I have my DMN definition using my custom function:

```
<definitions xmlns="http://www.omg.org/spec/DMN/20180521/MODEL/" id="definition_afbe03b6-6604-11eb-bbcf-0242ac110002" name="Next Business Day" namespace="http://www.flowable.org/dmn">
  <decision id="nextBusinessDay" name="Next Business Day">
    <decisionTable id="decisionTable_afbe03b6-6604-11eb-bbcf-0242ac110002" hitPolicy="FIRST">
      <input label="Date">
        <inputExpression id="inputExpression_1" typeRef="date">
          <text>inputVar</text>
        </inputExpression>
      </input>
      <output id="outputExpression_2" label="Next Business Day" name="nextBusinessDay" typeRef="date"></output>
      <rule>
        <inputEntry id="inputEntry_1_1">
          <text><![CDATA[-]]></text>
        </inputEntry>
        <outputEntry id="outputEntry_2_1">
          <text><![CDATA[dates:nextBusinessDay(inputVar)]]></text>
        </outputEntry>
      </rule>
    </decisionTable>
  </decision>
</definitions>

```

Thus when I try to execute the rule I get an error that says: “Could not resolve function ‘dates:nextBusinessDay’”

Thanks,  
Bruno Alves

---

<div class="post-metadata">

**Author:** ![yvo](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.flowable.org/yvo/32/2231_2.png) [@yvo](https://forum.flowable.org/u/yvo)\
**Post date:** [February 3, 2021, 3:12pm UTC](https://forum.flowable.org/t/dmn-create-a-custom-function/7446/2 "2021-02-03T15:12:01Z")

</div>

Hi,

problem seems that you’re setting the `customFlowableFunctionDelegates` after the DMN engine is initialised.  
If you want to use the `customFlowableFunctionDelegates` then you need to do it before initialisation because this is used to build up a collection FlowableFunctionDelegates. (The build in ones plus the custom ones).

> <https://github.com/flowable/flowable-engine/blob/master/modules/flowable-dmn-engine/src/main/java/org/flowable/dmn/engine/DmnEngineConfiguration.java#L422>

Please try a @configuration class like this one;

```auto
@Configuration
public class DmnEngineSetup {

    @Bean
    public EngineConfigurationConfigurer<SpringDmnEngineConfiguration> customDmnConfigurer() {

        return configuration -> {
            if (configuration.getCustomFlowableFunctionDelegates() == null) {
                configuration.setCustomFlowableFunctionDelegates(Collections.singletonList(new NextBusinessDay()));
            } else {
                configuration.getCustomFlowableFunctionDelegates().addAll(Collections.singletonList(new NextBusinessDay()));
            }
        };
    }
}

```

This adds the `NextbusinessDay` custom function delegate to the `DmnEngineConfiguration` before engine initialisation.

Regards,

Yvo

---

<div class="post-metadata">

**Author:** ![brunofigalveskk](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.flowable.org/brunofigalveskk/32/2230_2.png) [@brunofigalveskk](https://forum.flowable.org/u/brunofigalveskk)\
**Post date:** [February 3, 2021, 10:37pm UTC](https://forum.flowable.org/t/dmn-create-a-custom-function/7446/4 "2021-02-03T22:37:53Z")

</div>

Thank you for the response!  
This solves the problem 😀