SpringBoot整合Drools进行复杂业务决策与热更新实战

@Configuration
public class DroolsConfig {
    // 线程安全的容器引用
    private static final AtomicReference<KieContainer> CONTAINER_REF = new AtomicReference<>();
    @Bean(initMethod = "load")
    public DroolsEngine engine() {
        return new DroolsEngine();
    }
    public static StatelessKieSession openSession() {
        KieContainer container = CONTAINER_REF.get();
        if (container == null) throw new IllegalStateException("规则引擎未初始化或正在加载");
        // StatelessKieSession 每次创建成本极低，且线程安全，推荐按请求创建
        return container.newStatelessKieSession();
    }
}

@Slf4j
public class DroolsEngine {
    private final KieServices kieServices = KieServices.Factory.get();
    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();

    public void load() {
        rebuild(RuleConfigLoader.loadActiveDrls());
    }

    public void hotReload(List<String> drlContents) {
        rwLock.writeLock().lock();
        try {
            KieContainer old = DroolsConfig.CONTAINER_REF.get();
            KieContainer next = doCompile(drlContents);
            DroolsConfig.CONTAINER_REF.set(next);
            
            // 关键：释放旧容器，触发 ClassLoader 卸载，防内存泄漏
            if (old != null) {
                old.dispose();
                log.info("旧规则容器已释放");
            }
        } catch (Exception e) {
            log.error("热更新编译失败，保持当前版本", e);
            // 生产环境可在此处触发告警或回滚配置
        } finally {
            rwLock.writeLock().unlock();
        }
    }

    private KieContainer doCompile(List<String> drlContents) {
        KieFileSystem kfs = kieServices.newKieFileSystem();
        // KieFileSystem 是虚拟文件系统，路径随意，后缀必须正确
        for (int i = 0; i < drlContents.size(); i++) {
            kfs.write("rules/dynamic/rule_" + i + ".drl", drlContents.get(i));
        }
        
        KieBuilder builder = kieServices.newKieBuilder(kfs).buildAll();
        if (builder.getResults().hasMessages(Message.Level.ERROR)) {
            throw new IllegalStateException("DRL 语法错误: " + builder.getResults().getMessages());
        }
        return builder.getKieContainer();
    }
}

public class TraceableAgendaListener implements AgendaEventListener {
    @Override
    public void afterMatchFired(AfterMatchFiredEvent event) {
        Rule rule = event.getRule();
        // 结合 MDC 注入 TraceId，异步丢给 Kafka/ELK
        log.info("Rule triggered: {}, cost: {}ms", rule.getName(), event.getKieRuntime().getFactCount());
    }
}

package marketing.rules
import com.example.dto.OrderContext
import com.example.result.PromotionResult
global PromotionResult result

rule "VIP 满减互斥策略"
    agenda-group "promo"
    salience 90
    no-loop true
    when
        $ctx : OrderContext(userLevel == "VIP", amount > 500, conflictChecked == false)
    then
        result.applyDiscount("VIP_DISCOUNT", $ctx.amount * 0.15);
        modify($ctx) { setConflictChecked(true) };
end

public PromotionResult calculate(OrderRequest req) {
    OrderContext ctx = OrderConverter.toContext(req);
    PromotionResult res = new PromotionResult();
    
    try (StatelessKieSession session = DroolsConfig.openSession()) {
        session.setGlobal("result", res);
        session.getAgenda().getAgendaGroup("promo").setFocus();
        session.execute(ctx);
    }
    return res;
}