规则引擎之drools

    drools是一个规则引擎，可以将开发从业务中解放出来，不用重复写不同的业务、然后测试、上线，只需要将业务规则配置到drl文件，然后每次有新业务需求的时候，只需要改一下配置文件，项目不需要重新上线。drools帮你装载规则，解析规则，应用规则到你的业务。总之，使用drools你可以将业务规则的判定放在引擎里面去做，程序中只保留需要的业务数据。

    比如抽奖，其实抽奖每次规则都是差不多的，无非就是换个规则，比如新手大礼包，过生日，过节，然后就是礼品的类目、数量会变化，我们将这些业务数据放到facet里面，然后将规则配置到drl文件中，然后每次修改drl规则文件，拿到刚才说的那些业务数据，利用drools装载的规则进行判断，看用户是否中奖。

    这里提供一个例子，是活动相关的，根据数据的初始值匹配规则、执行规则、产生结果。

    1.drl配置文件

 

package promotionRule;

import mydrools.Promotion;


rule step1
    salience 100
    lock-on-active true
    when
        $promotionRule : Promotion(getPurchaseNum()== 0&&getGoodsName()=="机油")
    then
        $promotionRule.setPurchaseNum($promotionRule.getPurchaseNum()+10);
        $promotionRule.recordPointLog("只要是机油，就买10件");
end



rule step2
    salience 99
    lock-on-active true
    when
        $promotionRule : Promotion(goodsPrice < 100)
    then
        $promotionRule.setPurchaseNum($promotionRule.getPurchaseNum()+50);
        $promotionRule.recordPointLog("价格小于100，就多买50件");
end


rule step3
    //活动期限内，多买10件
    salience 90
    lock-on-active true

     date-effective "2017-01-08 23:59:59"
     date-expires "2017-08-08 23:59:59"

    when
        $promotionRule : Promotion(getPurchaseNum() < 1)
    then
        $promotionRule.setPurchaseNum($promotionRule.getPurchaseNum()+100);
        $promotionRule.recordPointLog("活动期限内，怎么着多买100件");
end

     2.规则接口     

 

 

public interface PromotionEngineRule {
    void initEngineRule();
    void executeEngineRule(Promotion prmotion);
    void refreshEngineRule();
}

    3.接口实现

 

  

public class PromotionEngineRuleImpl implements PromotionEngineRule {
private KnowledgeBase knowledgeBase;


    @Override
    public void initEngineRule() {
        System.out.println(" init start.....");
        // 设置时间格式
        System.setProperty("drools.dateformat", "yyyy-MM-dd HH:mm:ss");
        knowledgeBase=getKnowledgeBase();
        System.out.println(" init end");
    }

    @Override
    public void executeEngineRule(Promotion promotion) {
      StatefulKnowledgeSession sessions= knowledgeBase.newStatefulKnowledgeSession();
      sessions.insert(promotion);
        sessions.fireAllRules(new AgendaFilter() {
            @Override
            public boolean accept(Activation activation) {
                boolean result=false;
                if(activation.getRule().getName()!=null) {
                    result= true;
                }
               return result;
            }
        });
        sessions.dispose();

    }

    @Override
    public void refreshEngineRule() {
        System.out.println("refresh start ...");
        for(KnowledgePackage k:knowledgeBase.getKnowledgePackages()){
            knowledgeBase.removeKnowledgePackage(k.getName());
        }
        initEngineRule();
        System.out.println("refresh end");

    }


    public static KnowledgeBase getKnowledgeBase(){
        List<String> paths=getRulePath();
        KnowledgeBuilder builder= KnowledgeBuilderFactory.newKnowledgeBuilder();
        for(String path:paths){
            builder.add(ResourceFactory.newClassPathResource(path), ResourceType.DRL);
        }

        KnowledgeBuilderErrors errors=builder.getErrors();
        if(errors.size()>0){
            for(KnowledgeBuilderError error:errors){
                System.out.println(error);
            }
            throw new  IllegalArgumentException("can not parse knowledge");
        }

        KnowledgeBase kbase= KnowledgeBaseFactory.newKnowledgeBase();
        kbase.addKnowledgePackages(builder.getKnowledgePackages());
        return kbase;
    }


    public static List<String> getRulePath(){
        List<String> paths= Lists.newArrayList();
        paths.add("rules/promotionRule.drl");
        return paths;
    }


}

    4.测试

 

    

public class PromotionTest {
    public  static void  main(String[] args){

        Promotion p=new Promotion();
        PromotionEngineRule engine=new PromotionEngineRuleImpl();

        p.setPurchaseNum(0);
        p.setGoodsName("机油");
        p.setGoodsPrice(10);

        engine.initEngineRule();

        engine.executeEngineRule(p);

        engine.refreshEngineRule();
    }
}

 

 

   5.执行结果

     

init start.....
16:01:52,049 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback.groovy]
……..
 init end
只要是机油，就买10件，已买数量10
价格小于100，就多买50件，已买数量60
活动期限内，怎么着多买100件，已买数量160
refresh start ...
 init start.....
 init end
refresh end

   本文没有对drools语法做说明，不属于本文范围