// 傳統(tǒng)硬編碼方式（噩夢(mèng)般的代碼片段）
if(user.isVip()){  
    if(order.getAmount() > 200){  
        if(order.getItems().stream().anyMatch(i -> i.isPromotion())){  
            order.applyDiscount(0.8); // 會(huì)員滿200且含促銷商品打8折  
        }  
    } else if(order.getCreateTime().isAfter(LocalDate.of(2023,11,1))){  
        order.applyDiscount(0.9); // 雙十一期間會(huì)員專屬9折  
    }  
} else {  
    // 普通用戶規(guī)則嵌套層級(jí)更深...  
}

if(temperature > 50 || humidity > 80) {  
    if(pressure < 100 && vibration > 5) {  
        if(deviceStatus != Status.MAINTENANCE) {  
            triggerAlarm(AlarmLevel.CRITICAL);  
        }  
    }  
} else if (runtimeHours > 1000 && !isMaintained) {  
    triggerAlarm(AlarmLevel.WARNING);  
}  
// 后續(xù)還有8個(gè)else if...

public void refreshRules() {
    List<Rule> newRules = ruleLoader.loadFromDB(); // 從數(shù)據(jù)庫(kù)讀取最新規(guī)則
    rulesEngine.fire(new Rules(newRules), facts);  
}

[用戶類型] --> [VIP規(guī)則] --> [折扣計(jì)算]  
             \-> [普通用戶規(guī)則] --> [滿減計(jì)算]

# discount_rule.yml
name: "老用戶回饋規(guī)則"
description: "注冊(cè)超過(guò)3年的用戶額外折扣"
condition: "user.registerYears >= 3"
actions:
  - "order.applyAdditionalDiscount(0.95)"

public interface Rule {

    /**
    * 改方法封裝規(guī)則的條件（conditions）
    * @return 如果提供的事實(shí)適用于該規(guī)則返回true, 否則，返回false
    */
    boolean evaluate(Facts facts);

    /**
    * 改方法封裝規(guī)則的操作（actions）
    * @throws 如果在執(zhí)行過(guò)程中發(fā)生錯(cuò)誤將拋出Exception
    */
    void execute(Facts facts) throws Exception;

    //Getters and setters for rule name, description and priority omitted.

}

@Rule(name = "my rule", description = "my rule description", priority = 1)
publicclass MyRule {

    @Condition
    public boolean when(@Fact("fact") fact) {
        //my rule conditions
        returntrue;
    }

    @Action(order = 1)
    public void then(Facts facts) throws Exception {
        //my actions
    }

    @Action(order = 2)
    public void finally() throws Exception {
        //my final actions
    }

}

Rule rule = new RuleBuilder()
                .name("myRule")
                .description("myRuleDescription")
                .priority(3)
                .when(condition)
                .then(action1)
                .then(action2)
                .build();

Facts facts = new Facts();
facts.add("rain", true);

@Rule
class WeatherRule {

    @Condition
    public boolean itRains(@Fact("rain") boolean rain) {
        return rain;
    }

    @Action
    public void takeAnUmbrella(Facts facts) {
        System.out.println("It rains, take an umbrella!");
        // can add/remove/modify facts
    }

}

RulesEngine rulesEngine = new DefaultRulesEngine();
// or
RulesEngine rulesEngine = new InferenceRulesEngine();

rulesEngine.fire(rules, facts);

RulesEngineParameters parameters = new RulesEngineParameters()
    .rulePriorityThreshold(10)
    .skipOnFirstAppliedRule(true)
    .skipOnFirstFailedRule(true)
    .skipOnFirstNonTriggeredRule(true);

RulesEngine rulesEngine = new DefaultRulesEngine(parameters);

RulesEngineParameters parameters = myEngine.getParameters();

<dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-core</artifactId>
    <version>4.1.0</version>
</dependency>

public static void main(String[] args) {
    // 模擬傳感器數(shù)據(jù)（真實(shí)項(xiàng)目從MQTT獲?。?    Facts facts = new Facts();  // 事實(shí)對(duì)象（數(shù)據(jù)容器）
    facts.put("humidity", 85);  // 放入濕度值
    
    // 創(chuàng)建規(guī)則引擎（核心控制器）
    RulesEngine engine = new DefaultRulesEngine();
    
    // 裝載規(guī)則并執(zhí)行（點(diǎn)火?。?    engine.fire(new Rules(new RainRule()), facts); 
    
    // 執(zhí)行結(jié)果：
    // 【智能家居】檢測(cè)到濕度85%，建議關(guān)閉窗戶帶傘出門(mén)！
}

facts.put("temperature", 28);  
facts.put("location", "上海");

@Priority

@Rule(priority = 1) // 數(shù)字越大優(yōu)先級(jí)越高

@Action
public void remind() {
    System.out.println("規(guī)則觸發(fā)！"); // 先確認(rèn)是否執(zhí)行到此
}

// 一次性加載多個(gè)規(guī)則
Rules rules = new Rules(new RainRule(), new TempRule(), new WindRule());
engine.fire(rules, facts);

// 加載YAML規(guī)則
RulesLoader loader = new YamlRuleLoader();
Rules yamlRules = loader.load(new File("promotion_rules.yml"));

// 加載注解規(guī)則
Rules annoRules = new Rules(new ShareRule());

// 合并執(zhí)行
engine.fire(yamlRules, facts);
engine.fire(annoRules, facts);

@Rule(name = "技術(shù)緊急工單")
publicclass TechEmergencyRule {
    @Condition
    public boolean isTechEmergency(
            @Fact("ticket") Ticket ticket,
            @Fact("dutyTable") DutyTable table) {
        return ticket.getType() == TECH 
            && ticket.getPriority() == HIGH
            && table.hasAvailableTechLead();
    }
    
    @Action
    public void assignToTechLead() {
        String techLead = dutyTable.getCurrentTechLead();
        ticket.setAssignee(techLead);
        dutyTable.markBusy(techLead); // 標(biāo)記為忙碌狀態(tài)
    }
}

@Rule(name = "龍卷風(fēng)連擊")
publicclass TornadoComboRule {
    @Condition
    public boolean checkComboSequence(
            @Fact("queue") CircularFifoQueue<Skill> queue) {
        return queue.size() >=3
            && queue.get(0) == Skill.A
            && queue.get(1) == Skill.B
            && queue.get(2) == Skill.C;
    }
    
    @Action
    public void releaseSuperSkill() {
        player.cast(Skill.SUPER_TORNADO);
        queue.clear(); // 清空連招隊(duì)列
        effectPlayer.play("combo_success.wav");
    }
}

public abstract class BasePromotionRule implements Rule {
    @Condition
    public abstract boolean matchCondition(Order order);
    
    @Action
    public void applyDiscountTemplate(@Fact("order") Order order) {
        order.applyDiscount(getDiscountRate());
        log.info("應(yīng)用{}折扣", getRuleName());
    }
    
    protected abstract double getDiscountRate();
}

engine.registerRuleListener(new RuleListener() {
    public void beforeExecute(Rule rule, Facts facts) {
        Monitor.startTimer(rule.getName());
    }
    
    public void afterExecute(Rule rule, Facts facts) {
        long cost = Monitor.stopTimer(rule.getName());
        if(cost > 100) {
            alertSlowRule(rule.getName(), cost);
        }
    }
});

@Configuration  
publicclass RuleEngineConfig {  

    @Bean
    public RulesEngine rulesEngine() {  
        returnnew DefaultRulesEngine(  
            new Parameters()  
                .skipOnFirstNonTriggeredRule(true)  
                .priorityThreshold(10)  
        );  
    }  

    @Bean
    public Rules ruleRegistry() throws IOException {  
        // 自動(dòng)掃描帶@Rule注解的Bean  
        returnnew Rules(  
            new AnnotationRuleFactory().create(  
                new ClasspathRuleDefinitionReader(),  
                new ClassPathResource("rules/").getFile()  
            )  
        );  
    }  

    @Bean
    public ApplicationRunner ruleInitializer(RulesEngine engine, Rules rules) {  
        return args -> {  
            // 啟動(dòng)時(shí)預(yù)加載驗(yàn)證規(guī)則  
            engine.fire(rules, new Facts());  
            logger.info("已成功加載{}條規(guī)則", rules.size());  
        };  
    }  
}

@RestController  
publicclass PromotionController {  
    @Autowired
    private RulesEngine rulesEngine;  
    @Autowired
    private Rules rules;  

    @PostMapping("/apply-rules")  
    public Order applyRules(@RequestBody Order order) {  
        Facts facts = new Facts();  
        facts.put("order", order);  
        rulesEngine.fire(rules, facts);  
        return order;  
    }  
}