第6章 Other methods for creating and executing DRL rules

As an alternative to creating and managing DRL rules within the Business Central interface, you can create DRL rule files externally as part of a Maven or Java project using Red Hat CodeReady Studio or another integrated development environment (IDE). These standalone projects can then be integrated as knowledge JAR (KJAR) dependencies in existing Red Hat Decision Manager projects in Business Central. The DRL files in your standalone project must contain at a minimum the required package specification, import lists, and rule definitions. Any other DRL components, such as global variables and functions, are optional. All data objects related to a DRL rule must be included with your standalone DRL project or deployment.

You can also use executable rule models in your Maven or Java projects to provide a Java-based representation of a rule set for execution at build time. The executable model is a more efficient alternative to the standard asset packaging in Red Hat Decision Manager and enables KIE containers and KIE bases to be created more quickly, especially when you have large lists of DRL (Drools Rule Language) files and other Red Hat Decision Manager assets.

6.1. Creating and executing DRL rules in Red Hat CodeReady Studio

You can use Red Hat CodeReady Studio to create DRL files with rules and integrate the files with your Red Hat Decision Manager decision service. This method of creating DRL rules is helpful if you already use Red Hat CodeReady Studio 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.

Prerequisites

Procedure

  1. In the Red Hat CodeReady Studio, click FileNewProject.
  2. In the New Project window that opens, select DroolsDrools Project and click Next.
  3. Click the second icon to Create a project and populate it with some example files to help you get started quickly. Click Next.
  4. Enter a Project name and select the Maven radio button as the project building option. The GAV values are generated automatically. You can update these values as needed for your project:

    • Group ID: com.sample
    • Artifact ID: my-project
    • Version: 1.0.0-SNAPSHOT
  5. Click Finish to create the project.

    This configuration sets up a basic project structure, class path, and sample rules. The following is an overview of the project structure:

    my-project
     `-- src/main/java
        | `-- com.sample
        |    `-- DecisionTableTest.java
        |    `-- DroolsTest.java
        |    `-- ProcessTest.java
        |
     `-- src/main/resources
        | `-- dtables
        |    `-- Sample.xls
        | `-- process
        |    `-- sample.bpmn
        | `-- rules
        |    `-- Sample.drl
        | `-- META-INF
        |
     `-- JRE System Library
        |
     `-- Maven Dependencies
        |
     `-- Drools Library
        |
     `-- src
        |
     `-- target
        |
     `-- pom.xml

    Notice the following elements:

    • A Sample.drl rule file in the src/main/resources directory, containing an example Hello World and GoodBye rules.
    • A DroolsTest.java file under the src/main/java directory in the com.sample package. The DroolsTest class can be used to execute the Sample.drl rule.
    • The Drools Library directory, which acts as a custom class path containing JAR files necessary for execution.

    You can edit the existing Sample.drl file and DroolsTest.java files with new configurations as needed, or create new rule and object files. In this procedure, you are creating a new rule and new Java objects.

  6. Create a Java object on which the rule or rules will operate.

    In this example, a Person.java file is created in my-project/src/main/java/com.sample. 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:

      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;
        }
      }
  7. Click FileSave to save the file.
  8. Create a rule file in .drl format in my-project/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;
    
    import com.sample.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
  9. Click FileSave to save the file.
  10. Create a main class and save it to the same directory as the Java object that you created. The main class will load the KIE base and execute rules.

    注記

    You can also add the main() method and Person class within a single Java object file, similar to the DroolsTest.java sample file.

  11. In the main class, 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 main() method that passes the fact model to the rule.

    In this example, a RulesTest.java file is created in my-project/src/main/java/com.sample with the required imports and main() method:

    package com.sample;
    
    import org.kie.api.KieServices;
    import org.kie.api.runtime.KieContainer;
    import org.kie.api.runtime.KieSession;
    
    public class RulesTest {
      public static final void main(String[] args) {
        try {
          // 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();
        }
    
        catch (Throwable t) {
          t.printStackTrace();
        }
      }
    }
  12. Click FileSave to save the file.
  13. After you create and save all DRL assets in your project, right-click your project folder and select Run AsJava Application to build the project. If the project build fails, address any problems described in the Problems tab of the lower window in CodeReady Studio, and try again to validate the project until the project builds.
If the Run AsJava Application option is not available

If Java Application is not an option when you right-click your project and select Run As, then go to Run AsRun Configurations, right-click Java Application, and click New. Then in the Main tab, browse for and select your Project and the associated Main class. Click Apply and then click Run to test the project. The next time you right-click your project folder, the Java Application option will appear.

To integrate the new rule assets with an existing project in Red Hat Decision Manager, you can compile the new 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 Viewpom.xml.