初始规则引擎Drools

        规则引擎drools6.x和之前的版本变化很大，对规则引擎研究尚浅，对其中实现原理以及框架的具体结构不够了解，留着以后试着去慢慢研究，只是记录一下自己在实际中的应用。
        第一步我们创建一个工厂类，这个类来创建KieSession和StatelessKieSession对象。这两个对象是我们可以处理我们定义好的规则。现阶段我们只要认为这两个对象是根据我们的规则文件来创建。

package com.sun.util;

import org.drools.core.event.DebugRuleRuntimeEventListener;
import org.kie.api.KieBase;
import org.kie.api.KieServices;
import org.kie.api.builder.KieBuilder;
import org.kie.api.builder.KieFileSystem;
import org.kie.api.builder.Message;
import org.kie.api.io.Resource;
import org.kie.api.io.ResourceType;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;
import org.kie.api.runtime.StatelessKieSession;

public class KieSessionFactory {

  private static KieSession kieSession;

  private KieSessionFactory() {

  }
  /**
   * 
   * @title disposeKieSession
   * @description TODO (清空对象)
   * @return void
   */
  public static void disposeKieSession() {
    if (kieSession != null) {
      kieSession.dispose();
      kieSession = null;
    }

  }
  /**
   *创建KieSession对象
   */
  public static KieSession newKieSession(String classPath) throws Exception {

    KieServices kieServices = KieServices.Factory.get();
    KieFileSystem kfs = kieServices.newKieFileSystem();
    Resource resource = kieServices.getResources().newClassPathResource(classPath);
    resource.setResourceType(ResourceType.DRL);
    kfs.write(resource);
    KieBuilder kieBuilder = kieServices.newKieBuilder(kfs).buildAll();
    if (kieBuilder.getResults().getMessages(Message.Level.ERROR).size() > 0) {
      throw new Exception();
    }
    KieContainer kieContainer = kieServices.newKieContainer(kieServices.getRepository().getDefaultReleaseId());
    KieBase kBase = kieContainer.getKieBase();
    KieSession kieSession = kBase.newKieSession();
    kieSession.addEventListener(new DebugRuleRuntimeEventListener());
    return kieSession;

  }
  /**
   *创建StatelessKieSession 
   */
  public static StatelessKieSession newStatelessKieSession(String classPath) throws Exception {
    KieServices kieServices = KieServices.Factory.get();
    KieFileSystem kfs = kieServices.newKieFileSystem();
    Resource resource = kieServices.getResources().newClassPathResource(classPath);
    resource.setResourceType(ResourceType.DRL);
    kfs.write(resource);
    KieBuilder kieBuilder = kieServices.newKieBuilder(kfs).buildAll();
    if (kieBuilder.getResults().getMessages(Message.Level.ERROR).size() > 0) {
      throw new Exception();
    }
    KieContainer kieContainer = kieServices.newKieContainer(kieServices.getRepository().getDefaultReleaseId());
    KieBase kBase = kieContainer.getKieBase();
    StatelessKieSession kiesession = kBase.newStatelessKieSession();
    return kiesession;

  }
}

        第二步定义规则文件，规则文件是*.drl格式，规则文件有自己的具体语法和关键词，我们通过查看drools的API来进行详细的了解。建议将规则文件定义到类路径下面。

package com.company.license

//list any import classes here.
import bean.Applicant;

import bean.Application;
//declare any global variables here

rule "Is of valid age"
	salience 1
	lock-on-active true
    when
         a: Applicant( age < 18 )
    then
    	a.setValid(false);
end

rule "pass valid age"
	salience 1
	lock-on-active true
    when
         a: Applicant( age >= 18 )
    then
    	a.setValid(true);
end

rule "Application was made this year"
when
    $a : Application( dateApplied > "01-jan-2009" )     
then
    $a.setValid( false );
end

        第三步来创建两个JavaBean对象，这是我们上面规则文件中引用的两个对象。

public class Applicant {
  private String name;
  private int age;
  private boolean valid;
  public Applicant() {

  }
  public Applicant(String name, int age) {
    this.name = name;
    this.age = age;
  }

  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 isValid() {
    return valid;
  }

  public void setValid(boolean valid) {
    this.valid = valid;
  }
}

public class Application {

  private Date dateApplied;
  private boolean valid;

  public Date getDateApplied() {
    return dateApplied;
  }

  public void setDateApplied(Date dateApplied) {
    this.dateApplied = dateApplied;
  }

  public boolean isValid() {
    return valid;
  }

  public void setValid(boolean valid) {
    this.valid = valid;
  }

}

        这里我们初次使用StatelessKieSession来调用我们的规则

 KieServices kieServices = KieServices.Factory.get();
    StatelessKieSession kSession = KieSessionFactory.newStatelessKieSession("resources/test.drl");
    Applicant applicant = new Applicant("Mr John Smith", 16);
    Application application = new Application();
    /**
     * 多个对象
     */
    kSession.execute(Arrays.asList(new Object[] { application, applicant }));
    if (applicant.isValid()) {
      System.out.println("pass");
    } else {
      System.out.println("pass denied");
    }
    System.out.println(application.isValid());

    KieCommands kieCommands = kieServices.getCommands();
    @SuppressWarnings("rawtypes")
    List<Command> cmds = new ArrayList<Command>();
    cmds.add(kieCommands.newInsert(new Applicant("Mr John Smith", 19), "mrSmith", true, null));
    ExecutionResults results = kSession.execute(kieCommands.newBatchExecution(cmds));
    applicant = (Applicant) results.getValue("mrSmith");
    System.out.println(applicant.isValid());