if (规则条件1){//处理1
}
else if (规则条件2){//处理2
}
else if (规则条件3){//处理3
}
...

    <properties><drools.version>6.5.0.Final</drools.version><lombok.version>1.18.2</lombok.version></properties><dependencies><dependency><groupId>org.drools</groupId><artifactId>drools-compiler</artifactId><version>${drools.version}</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>${lombok.version}</version></dependency></dependencies>

package com.cnblogs.yjmyzz.drools.demo.model;import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.Setter;@Setter
@Getter
@AllArgsConstructor
public class Message {public enum MessageType {HI,GOODBYE,CHAT}private MessageType messageType;private String target;}　　

package com.cnblogs.yjmyzz.drools;import com.cnblogs.yjmyzz.drools.demo.model.Message;
import java.util.concurrent.atomic.AtomicInteger;global String temp;
global AtomicInteger count;//函数示例
function void print(String messgae){System.out.println(messgae);
}//规则1
rule "say-hi"when$message: Message(Message.MessageType.HI.equals(messageType) && target!=null)thenprint("hi," + $message.getTarget() + ", welcome to drools\n");end

package com.cnblogs.yjmyzz.drools;import com.cnblogs.yjmyzz.drools.demo.model.Message;
import java.util.concurrent.atomic.AtomicInteger;global String temp;
global AtomicInteger count;//函数示例
function void print(String messgae){System.out.println(messgae);
}//规则1
rule "say-hi"when$message: Message(Message.MessageType.HI.equals(messageType) && target!=null)thenprint("hi," + $message.getTarget() + ", welcome to drools\n");endrule "say-goodbye"when$message: Message(Message.MessageType.GOODBYE.equals(messageType) && target!=null)thenprint("bye bye ," + $message.getTarget() + "\n");endrule "chat-and-goodbye"when$message: Message(Message.MessageType.CHAT.equals(messageType) && target!=null)thenprint($message.getTarget() +  ", nice to meet you. But I have to go.");//将MessageType设置成GOODBYE$message.setMessageType(Message.MessageType.GOODBYE);//更新fact,以便触发规则"say-goodbye"update($message);endrule "give-me-money"salience -1 //规则触发的优先级，值越大，越先触发when$message: Message(target.equals("beggar"))thenprint("5毛拿好");endrule "give-me-rice"salience 1when$message: Message(target.equals("beggar"))thenprint("给你个包子吧");end//本规则的效果：如果target="loop"，会循环触发，真到10次后停下
rule "loop"
//    no-loop  //加上这行后，将禁止循环触发when$message: Message(target.equals("loop") && count.get()<10)thenprint("\n我会每隔1秒触发，10次后停止！" + count.addAndGet(1));Thread.sleep(1000);update($message)end

package com.cnblogs.yjmyzz.drools;import com.cnblogs.yjmyzz.drools.demo.model.Message;rule "global-demo"salience -99when$message: Message(target.equals("beggar"))thenSystem.out.println(temp);end

<?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns="http://jboss.org/kie/6.0.0/kmodule"><kbase name="hello" packages="hello"><ksession name="ksession-hello"/></kbase>
</kmodule>

package com.cnblogs.yjmyzz.drools.demo;import com.cnblogs.yjmyzz.drools.demo.model.Message;
import org.kie.api.KieServices;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;import java.util.concurrent.atomic.AtomicInteger;public class HelloApp {public static void main(String[] args) {KieContainer kContainer = null;try {KieServices ks = KieServices.Factory.get();kContainer = ks.getKieClasspathContainer();KieSession kSession = kContainer.newKieSession("ksession-hello");Message message1 = new Message(Message.MessageType.HI, "杨过");kSession.insert(message1);kSession.fireAllRules();Message message2 = new Message(Message.MessageType.GOODBYE, "姑姑");kSession.insert(message2);kSession.fireAllRules();Message message3 = new Message(Message.MessageType.CHAT, "美羊羊");kSession.insert(message3);kSession.fireAllRules();Message message4 = new Message(null, "beggar");kSession.setGlobal("temp", "我是谁？我在哪？我要干什么？");kSession.insert(message4);kSession.fireAllRules();Message message5 = new Message(null, "loop");kSession.setGlobal("count", new AtomicInteger(0));kSession.insert(message5);kSession.fireAllRules();} catch (Exception e) {e.printStackTrace();} finally {if (kContainer != null) {kContainer.dispose();}}}
}

hi,杨过, welcome to drools //规则：say-hibye bye ,姑姑 //规则：say-goodbye美羊羊, nice to meet you. But I have to go. //规则：chat-and-goodbye
bye bye ,美羊羊 //规则: say-goodbye(2次匹配成功）给你个包子吧 //规则：give-me-rice
5毛拿好 //规则：give-me-money
我是谁？我在哪？我要干什么？//hello2.drl中的规则"global-demo"我会每隔1秒触发，10次后停止！1 //规则:loop循环10次我会每隔1秒触发，10次后停止！2我会每隔1秒触发，10次后停止！3我会每隔1秒触发，10次后停止！4我会每隔1秒触发，10次后停止！5我会每隔1秒触发，10次后停止！6我会每隔1秒触发，10次后停止！7我会每隔1秒触发，10次后停止！8我会每隔1秒触发，10次后停止！9我会每隔1秒触发，10次后停止！10

小明历险记：规则引擎drools教程一 
drools 6.5.0官方文档 
Learn Drools: Part I
Learn Drools: Part II (Cross Product)
Learn Drools: Part III (Filter Facts)
Learn Drools (Part 4): Inferences
Learn Drools (Part 5): Truth Maintenance
Learn Drools (Part 6): Rules and Statistics
Learn Drools (Part 7): Salience
Drools语法篇之Global全局变量
《Drools7.0.0.Final规则引擎教程》第4章 global全局变量

附：文件示例代码drools-helloworld可从github下载