如何用Java开发规则引擎？Drools决策表配置

<dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-core</artifactId>
    <version>7.x.x.Final</version>
</dependency>
<dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-compiler</artifactId>
    <version>7.x.x.Final</version>
</dependency>
<dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-decisiontables</artifactId>
    <version>7.x.x.Final</version>
</dependency>

import org.kie.api.KieServices;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;
import org.kie.api.builder.KieFileSystem;
import org.kie.api.builder.ReleaseId;
import org.kie.api.builder.KieBuilder;
import org.kie.internal.io.ResourceFactory;

// 假设有一个简单的Order类
public class Order {
    private double amount;
    private String item;
    private double discount;
    private String message;

    // 构造函数，getter/setter省略
    public Order(double amount, String item) {
        this.amount = amount;
        this.item = item;
    }

    public double getAmount() { return amount; }
    public void setAmount(double amount) { this.amount = amount; }
    public String getItem() { return item; }
    public void setItem(String item) { this.item = item; }
    public double getDiscount() { return discount; }
    public void setDiscount(double discount) { this.discount = discount; }
    public String getMessage() { return message; }
    public void setMessage(String message) { this.message = message; }

    @Override
    public String toString() {
        return "Order{" +
               "amount=" + amount +
               ", item='" + item + '\'' +
               ", discount=" + discount +
               ", message='" + message + '\'' +
               '}';
    }
}

public class DroolsDecisionTableExample {

    public static void main(String[] args) {
        KieServices ks = KieServices.Factory.get();
        KieFileSystem kfs = ks.newKieFileSystem();

        // 加载决策表文件
        // 这里假设 rules.xls 在 resources 目录下
        kfs.write(ResourceFactory.newClassPathResource("rules.xls"));

        KieBuilder kb = ks.newKieBuilder(kfs).buildAll();
        if (kb.getResults().hasMessages(org.kie.api.builder.Message.Level.ERROR)) {
            throw new RuntimeException("Build Errors:\n" + kb.getResults().toString());
        }

        // 获取KieContainer
        KieContainer kContainer = ks.newKieContainer(ks.getRepository().getDefaultReleaseId());
        // 获取KieSession
        KieSession kSession = kContainer.newKieSession();

        // 创建事实对象
        Order order1 = new Order(1200, "Laptop");
        Order order2 = new Order(600, "Mouse");
        Order order3 = new Order(300, "Keyboard");

        // 插入事实
        kSession.insert(order1);
        kSession.insert(order2);
        kSession.insert(order3);

        // 触发规则
        kSession.fireAllRules();

        // 打印结果
        System.out.println("Order 1: " + order1);
        System.out.println("Order 2: " + order2);
        System.out.println("Order 3: " + order3);

        // 关闭session
        kSession.dispose();
    }
}

| CONDITION | ACTION | salience |
|---|---|---|
| Amount > | Discount = | 100 |
| 1000 | 0.1 | |
| CustomerType == | Discount = | 200 |
| "VIP" | 0.15 | |

// 动态加载规则的简化示例
public KieSession loadRulesFromDatabase(String ruleContent) {
    KieServices ks = KieServices.Factory.get();
    KieFileSystem kfs = ks.newKieFileSystem();
    // 假设ruleContent是从数据库读取的Excel二进制流
    // 或者直接是DRL字符串，这里需要根据实际情况转换
    kfs.write("src/main/resources/rules.xls", ResourceFactory.newByteArrayResource(ruleContent.getBytes()));

    KieBuilder kb = ks.newKieBuilder(kfs).buildAll();
    if (kb.getResults().hasMessages(org.kie.api.builder.Message.Level.ERROR)) {
        System.err.println("Rule compilation errors: " + kb.getResults().toString());
        return null;
    }
    KieContainer kContainer = ks.newKieContainer(ks.getRepository().getDefaultReleaseId());
    return kContainer.newKieSession();
}