6.3. Creating and executing DRL rules using Maven

You can use Maven archetypes to create DRL files with rules and integrate the archetypes with your Red Hat Decision Manager decision service. This method of creating DRL rules is helpful if you already use external Maven archetypes for your decision service and want to continue with the same workflow. If you do not already use this method, then the Business Central interface of Red Hat Decision Manager is recommended for creating DRL files and other rule assets.

Procedure

  1. Navigate to a directory where you want to create a Maven archetype and run the following command: 

    mvn archetype:generate -DgroupId=com.sample.app -DartifactId=my-app -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

    This creates a directory my-app with the following structure: 

    my-app
|-- pom.xml
`-- src
    |-- main
    |   `-- java
    |       `-- com
    |           `-- sample
    |               `-- app
    |                   `-- App.java
    `-- test
        `-- java
            `-- com
                `-- sample
                    `-- app
                        `-- AppTest.java

    The my-app directory contains the following key components:

    • A src/main directory for storing the application sources
    • A src/test directory for storing the test sources
    • A pom.xml file with the project configuration

  2. Create a Java object on which the rule or rules will operate within the Maven archetype.

    In this example, a Person.java file is created in the directory my-app/src/main/java/com/sample/app. The Person class contains getter and setter methods to set and retrieve the first name, last name, hourly rate, and the wage of a person: 

    package com.sample.app;

  public class Person {

    private String firstName;
    private String lastName;
    private Integer hourlyRate;
    private Integer wage;

    public String getFirstName() {
      return firstName;
    }

    public void setFirstName(String firstName) {
      this.firstName = firstName;
    }

    public String getLastName() {
      return lastName;
    }

    public void setLastName(String lastName) {
      this.lastName = lastName;
    }

    public Integer getHourlyRate() {
      return hourlyRate;
    }

    public void setHourlyRate(Integer hourlyRate) {
      this.hourlyRate = hourlyRate;
    }

    public Integer getWage(){
      return wage;
    }

    public void setWage(Integer wage){
      this.wage = wage;
    }
  }

  3. Create a rule file in .drl format in my-app/src/main/resources/rules. The DRL file must contain at a minimum a package specification, an import list of data objects to be used by the rule or rules, and one or more rules with when conditions and then actions.

    The following Wage.drl file contains a Wage rule that imports the Person class, calculates the wage and hourly rate values, and displays a message based on the result: 

    package com.sample.app;

import com.sample.app.Person;

dialect "java"

rule "Wage"
  when
    Person(hourlyRate * wage > 100)
    Person(name : firstName, surname : lastName)
  then
    System.out.println("Hello " + name + " " + surname + "!");
    System.out.println("You are rich!");
end

  4. In the my-app/src/main/resources/META-INF directory, create a kmodule.xml metadata file with the following content: 

    <?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns="http://www.drools.org/xsd/kmodule">
</kmodule>

    This kmodule.xml file is a KIE module descriptor that selects resources to KIE bases and configures sessions. This file enables you to define and configure one or more KIE bases, and to include DRL files from specific packages in a specific KIE base. You can also create one or more KIE sessions from each KIE base.

    The following example shows a more advanced kmodule.xml file: 

    <?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.drools.org/xsd/kmodule">
  <kbase name="KBase1" default="true" eventProcessingMode="cloud" equalsBehavior="equality" declarativeAgenda="enabled" packages="org.domain.pkg1">
    <ksession name="KSession1_1" type="stateful" default="true" />
    <ksession name="KSession1_2" type="stateful" default="true" beliefSystem="jtms" />
  </kbase>
  <kbase name="KBase2" default="false" eventProcessingMode="stream" equalsBehavior="equality" declarativeAgenda="enabled" packages="org.domain.pkg2, org.domain.pkg3" includes="KBase1">
    <ksession name="KSession2_1" type="stateless" default="true" clockType="realtime">
      <fileLogger file="debugInfo" threaded="true" interval="10" />
      <workItemHandlers>
        <workItemHandler name="name" type="new org.domain.WorkItemHandler()" />
      </workItemHandlers>
      <listeners>
        <ruleRuntimeEventListener type="org.domain.RuleRuntimeListener" />
        <agendaEventListener type="org.domain.FirstAgendaListener" />
        <agendaEventListener type="org.domain.SecondAgendaListener" />
        <processEventListener type="org.domain.ProcessListener" />
      </listeners>
    </ksession>
  </kbase>
</kmodule>

    This example defines two KIE bases. Two KIE sessions are instantiated from the KBase1 KIE base, and one KIE session from KBase2. The KIE session from KBase2 is a stateless KIE session, which means that data from a previous invocation of the KIE session (the previous session state) is discarded between session invocations. Specific packages of rule assets are included with both KIE bases. When you specify packages in this way, you must organize your DRL files in a folder structure that reflects the specified packages.

  5. In the my-app/pom.xml configuration file, specify the libraries that your application requires. Provide the Red Hat Decision Manager dependencies as well as the group ID, artifact ID, and version (GAV) of your application. 

    <?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>my-app</artifactId>
<version>1.0.0</version>
<repositories>
  <repository>
    <id>jboss-ga-repository</id>
    <url>http://maven.repository.redhat.com/ga/</url>
  </repository>
</repositories>
<dependencies>
  <dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-compiler</artifactId>
    <version>VERSION</version>
  </dependency>
  <dependency>
    <groupId>org.kie</groupId>
    <artifactId>kie-api</artifactId>
    <version>VERSION</version>
  </dependency>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
  </dependency>
</dependencies>
</project>

    For information about Maven dependencies and the BOM (Bill of Materials) in Red Hat Decision Manager, see What is the mapping between Red Hat Decision Manager and Maven library version?.

  6. Use the testApp method in my-app/src/test/java/com/sample/app/AppTest.java to test the rule. The AppTest.java file is created by Maven by default.

  7. In the AppTest.java file, add the required import statements to import KIE services, a KIE container, and a KIE session. Then load the KIE base, insert facts, and execute the rule from the testApp() method that passes the fact model to the rule. 

    import org.kie.api.KieServices;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;

public void testApp() {

  // Load the KIE base:
  KieServices ks = KieServices.Factory.get();
  KieContainer kContainer = ks.getKieClasspathContainer();
  KieSession kSession = kContainer.newKieSession();

  // Set up the fact model:
  Person p = new Person();
  p.setWage(12);
  p.setFirstName("Tom");
  p.setLastName("Summers");
  p.setHourlyRate(10);

  // Insert the person into the session:
  kSession.insert(p);

  // Fire all rules:
  kSession.fireAllRules();
  kSession.dispose();
}

  8. After you create and save all DRL assets in your Maven archetype, navigate to the my-app directory in the command line and run the following command to build your files: 

    mvn clean install

    If the build fails, address any problems described in the command line error messages and try again to validate the files until the build is successful.

  9. After your files build successfully, run the following command to execute the rules locally. Replace com.sample.app with your package name. 

    mvn exec:java -Dexec.mainClass="com.sample.app"
  10. Review the rules to ensure that they executed properly, and address any needed changes in the files.

To integrate the new rule assets with an existing project in Red Hat Decision Manager, you can compile the new Maven project as a knowledge JAR (KJAR) and add it as a dependency in the pom.xml file of the project in Business Central. To access the project pom.xml file in Business Central, you can select any existing asset in the project and then in the Project Explorer menu on the left side of the screen, click the Customize View gear icon and select Repository View → pom.xml.