drools简单示例

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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");endrule 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");endrule 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160refresh start ... init start..... init endrefresh end

本文没有对drools语法做说明，不属于本文范围

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