Rule service in 15 minutes

Prerequisites

Procedure

After you create your project, you can create or import Decision Model and Notation (DMN) decision models and Drools Rule Language (DRL) business rules in the src/main/resources folder of your project. You can also include Java classes in the src/main/java folder of your project that act as Java services or provide implementations that can be called from decisions.

The example for this procedure is a basic Business Rule microservice that provides a REST endpoint /persons. This endpoint is automatically generated based on an example PersonDecisions.dmn DMN model to make decisions based on the data being processed.

The business Decision contains the decision logic of the Business Service. You can define business rules and decisions in different ways, such as with DMN Decisions or DRL Rules. The example for this procedure uses a DMN model.

In the Maven project that was created in the Initial Business Service project setup section, navigate to the src/main/java/com/ibm folder and add the following Person.java file:

Example person Java object

package com.ibm;

import java.io.Serializable;

public class Person {

	private String name;
	private int age;
	private boolean adult;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public boolean isAdult() {
		return adult;
	}

	public void setAdult(boolean adult) {
		this.adult = adult;
	}

	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", adult=" + adult + "]";
	}

}

This example Java object sets and retrieves a person’s name, age, and adult status.

Navigate to the src/main/resources folder and add the following PersonDecisions.dmn DMN decision model or continue to create it from scratch:

Example PersonDecisions DMN file

<dmn:definitions xmlns:dmn="http://www.omg.org/spec/DMN/20180521/MODEL/" xmlns="https://kiegroup.org/dmn/_52CEF9FD-9943-4A89-96D5-6F66810CA4C1" xmlns:di="http://www.omg.org/spec/DMN/20180521/DI/" xmlns:kie="http://www.drools.org/kie/dmn/1.2" xmlns:dmndi="http://www.omg.org/spec/DMN/20180521/DMNDI/" xmlns:dc="http://www.omg.org/spec/DMN/20180521/DC/" xmlns:feel="http://www.omg.org/spec/DMN/20180521/FEEL/" id="_84B432F5-87E7-43B1-9101-1BAFE3D18FC5" name="PersonDecisions" typeLanguage="http://www.omg.org/spec/DMN/20180521/FEEL/" namespace="https://kiegroup.org/dmn/_52CEF9FD-9943-4A89-96D5-6F66810CA4C1">
  <dmn:extensionElements/>
  <dmn:itemDefinition id="_DEF2C3A7-F3A9-4ABA-8D0A-C823E4EB43AB" name="tPerson" isCollection="false">
    <dmn:itemComponent id="_DB46DB27-0752-433F-ABE3-FC9E3BDECC97" name="Age" isCollection="false">
      <dmn:typeRef>number</dmn:typeRef>
    </dmn:itemComponent>
    <dmn:itemComponent id="_8C6D865F-E9C8-43B0-AB4D-3F2075A4ECA6" name="Name" isCollection="false">
      <dmn:typeRef>string</dmn:typeRef>
    </dmn:itemComponent>
    <dmn:itemComponent id="_9033704B-4E1C-42D3-AC5E-0D94107303A1" name="Adult" isCollection="false">
      <dmn:typeRef>boolean</dmn:typeRef>
    </dmn:itemComponent>
  </dmn:itemDefinition>
  <dmn:inputData id="_F9685B74-0C69-4982-B3B6-B04A14D79EDB" name="Person">
    <dmn:extensionElements/>
    <dmn:variable id="_0E345A3C-BB1F-4FB2-B00F-C5691FD1D36C" name="Person" typeRef="tPerson"/>
  </dmn:inputData>
  <dmn:decision id="_0D2BD7A9-ACA1-49BE-97AD-19699E0C9852" name="isAdult">
    <dmn:extensionElements/>
    <dmn:variable id="_54CD509F-452F-40E5-941C-AFB2667D4D45" name="isAdult" typeRef="boolean"/>
    <dmn:informationRequirement id="_2F819B03-36B7-4DEB-AED6-2B46AE3ADB75">
      <dmn:requiredInput href="#_F9685B74-0C69-4982-B3B6-B04A14D79EDB"/>
    </dmn:informationRequirement>
    <dmn:decisionTable id="_58370567-05DE-4EC0-AC2D-A23803C1EAAE" hitPolicy="UNIQUE" preferredOrientation="Rule-as-Row">
      <dmn:input id="_ADEF36CD-286A-454A-ABD8-9CF96014021B">
        <dmn:inputExpression id="_4930C2E5-7401-46DD-8329-EAC523BFA492" typeRef="number">
          <dmn:text>Person.Age</dmn:text>
        </dmn:inputExpression>
      </dmn:input>
      <dmn:output id="_9867E9A3-CBF6-4D66-9804-D2206F6B4F86" typeRef="boolean"/>
      <dmn:rule id="_59D6BFF0-35B4-4B7E-8D7B-E31CB0DB8242">
        <dmn:inputEntry id="_7DC55D63-234F-497B-A12A-93DA358C0136">
          <dmn:text>&gt; 18</dmn:text>
        </dmn:inputEntry>
        <dmn:outputEntry id="_B3BB5B97-05B9-464A-AB39-58A33A9C7C00">
          <dmn:text>true</dmn:text>
        </dmn:outputEntry>
      </dmn:rule>
      <dmn:rule id="_8FCD63FE-8AD8-4F56-AD12-923E87AFD1B1">
        <dmn:inputEntry id="_B4EF7F13-E486-46CB-B14E-1D21647258D9">
          <dmn:text>&lt;= 18</dmn:text>
        </dmn:inputEntry>
        <dmn:outputEntry id="_F3A9EC8E-A96B-42A0-BF87-9FB1F2FDB15A">
          <dmn:text>false</dmn:text>
        </dmn:outputEntry>
      </dmn:rule>
    </dmn:decisionTable>
  </dmn:decision>
  <dmndi:DMNDI>
    <dmndi:DMNDiagram>
      <di:extension>
        <kie:ComponentsWidthsExtension>
          <kie:ComponentWidths dmnElementRef="_58370567-05DE-4EC0-AC2D-A23803C1EAAE">
            <kie:width>50</kie:width>
            <kie:width>100</kie:width>
            <kie:width>100</kie:width>
            <kie:width>100</kie:width>
          </kie:ComponentWidths>
        </kie:ComponentsWidthsExtension>
      </di:extension>
      <dmndi:DMNShape id="dmnshape-_F9685B74-0C69-4982-B3B6-B04A14D79EDB" dmnElementRef="_F9685B74-0C69-4982-B3B6-B04A14D79EDB" isCollapsed="false">
        <dmndi:DMNStyle>
          <dmndi:FillColor red="255" green="255" blue="255"/>
          <dmndi:StrokeColor red="0" green="0" blue="0"/>
          <dmndi:FontColor red="0" green="0" blue="0"/>
        </dmndi:DMNStyle>
        <dc:Bounds x="404" y="464" width="100" height="50"/>
        <dmndi:DMNLabel/>
      </dmndi:DMNShape>
      <dmndi:DMNShape id="dmnshape-_0D2BD7A9-ACA1-49BE-97AD-19699E0C9852" dmnElementRef="_0D2BD7A9-ACA1-49BE-97AD-19699E0C9852" isCollapsed="false">
        <dmndi:DMNStyle>
          <dmndi:FillColor red="255" green="255" blue="255"/>
          <dmndi:StrokeColor red="0" green="0" blue="0"/>
          <dmndi:FontColor red="0" green="0" blue="0"/>
        </dmndi:DMNStyle>
        <dc:Bounds x="404" y="311" width="100" height="50"/>
        <dmndi:DMNLabel/>
      </dmndi:DMNShape>
      <dmndi:DMNEdge id="dmnedge-_2F819B03-36B7-4DEB-AED6-2B46AE3ADB75" dmnElementRef="_2F819B03-36B7-4DEB-AED6-2B46AE3ADB75">
        <di:waypoint x="504" y="489"/>
        <di:waypoint x="404" y="336"/>
      </dmndi:DMNEdge>
    </dmndi:DMNDiagram>
  </dmndi:DMNDI>
</dmn:definitions>

This example DMN model consists of a basic DMN input node and a decision node defined by a DMN Decision Table with a custom structured data type.

In VS Code, you can add the BAMOE Developer Tools for VS Code to design the decision requirements diagram (DRD), boxed expression, and data types with the DMN Editor.

To create this DMN model example in VS Code using the DMN Editor, follow these steps:

Create a PersonDecisions.dmn file, after the editor finishes loading, click the Properties icon in the upper-right corner of the DMN Editor, and confirm that the DMN model Name is set to PersonDecisions.
In the left palette, select DMN Input Data, drag the node to the diagram, and double-click the node to name it Person.
In the left palette, drag the DMN Decision node to the diagram, double-click the node to name it isAdult, and link to it from the input node.

Figure 1. Example PersonDecisions DMN decision requirements diagram (DRD)
In the upper tab options, select the Data Types tab and add the following tPerson structured data type and nested data types:

Figure 2. Example DMN Data Types
After you define the data types, select the Editor tab to return to the DMN Editor diagram.
Select the Person input node, click the Properties icon, and under Information item, set the Data type to tPerson.
Select the isAdult decision node, click the Properties icon, and under Information item, set the Data type to boolean.
Select the decision node to display the node options and click the Edit icon to open the DMN boxed expression editor to define the decision logic for the node.
Click the undefined expression field and select Decision Table.
Click the upper-left corner of the Decision Table to set the hit policy to Unique.
Set the input and output columns so that the input source Person.Age with type number determines the age limit and the output target isAdult with type boolean determines adult status:

Figure 3. Example DMN Decision Table for isAdult Decision
Save the DMN decision file.

With everything in place, you can start the Quarkus server with the following command in the project root:
```
mvn quarkus:dev
```
Then you can check the application Swagger UI at http://localhost:8080/q/swagger-ui/#/