第20章 Other methods for creating and executing DRL rules

Procedure

1. In the Red Hat CodeReady Studio, click File New Project.
2. In the New Project window that opens, select Drools Drools 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 File Save 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 File Save 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 File Save to save the file.
13. After you create and save all DRL assets in your project, right-click your project folder and select Run As Java 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.