jbang drools.java

drools.java

///usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS org.drools:drools-engine:7.56.0.Final
//DEPS org.drools:drools-mvel:7.56.0.Final
//DEPS org.drools:drools-mvel:7.56.0.Final
//DEPS org.slf4j:slf4j-nop:1.7.31
//DEPS com.fasterxml.jackson.core:jackson-databind:2.12.3

// example
// jbang <url> '{ "name":"Mario", "age":40 }' '{ "name":"Mark", "age":37 }'

package org.kie.example;

import static java.lang.System.*;
import org.kie.api.*;
import org.kie.api.builder.*;
import org.kie.api.runtime.*;
import com.fasterxml.jackson.databind.ObjectMapper;


public class drools {
    public static record Person(String name, int age) {}

    final static String drl = """
    package org.kie.example;
    import org.kie.example.drools.*;

    rule MyRule when
       $mark: Person(name == "Mark")
       $older: Person(name != "Mark" && age > $mark.age)
    then
        System.out.printf("%s is older than %s", $older.name(), $mark.name());
        System.out.println();
    end

    """;

    public static void main(String... args) throws Exception {
        var mapper = new ObjectMapper();
        var kieSession = makeSession();
        for (var s: args) {
            var person = mapper.readValue(s, Person.class);
            kieSession.insert(person);
        }

        kieSession.fireAllRules();
        kieSession.dispose();
    }

    static KieSession makeSession() {
        var kieServices = KieServices.Factory.get();
        var kfs = kieServices.newKieFileSystem();
        kfs.write("src/main/resources/rules.drl",
            kieServices.getResources().newReaderResource(new java.io.StringReader(drl)));
        var kieBuilder = kieServices.newKieBuilder(kfs).buildAll();

        var results = kieBuilder.getResults();
        if(results.hasMessages(Message.Level.ERROR)){
            err.println("Errors building the rule base.");
            err.println(results.getMessages());
            System.exit(-1);
        }
        return kieServices
                    .newKieContainer(kieBuilder.getKieModule().getReleaseId())
                    .newKieSession();
    }
}