规则引擎java 推荐 规则引擎easy rule

接触过Drools的同学都会被复杂的Api给难住，简直就是入门到放弃的一个过程，而EasyRule就是Drools的简化版，裁剪了部分使用场景非常少的复杂功能，也简化了很多Drools中的组件，这样我们在使用EasyRule的时候对于API理解就非常容易了

什么是Easy Rules？

Easy Rules是一个简单的JAVA开源规则引擎，它提供了规则抽象来创建带有评估条件和执行操作的规则，规则引擎API通过运行一组规则以评估条件和执行操作。

框架特点

• 轻量级类库
• 容易学习的API
• 基于POJO的注解编程模型开发
• 通过高效的抽象来定义业务规则并易于用JAVA应用它们
• 支持通过原始规则创建复合规则
• 支持用表达式语言定义规则

功能组件

• 事实（Fact）：业务数据，结构类似HashMap；
• 规则（Rule）：业务规则，包含条件评估、动作执行，条件评估结果为true，则执行对应动作；
• 规则引擎（Rule Engine）：以指定的方式执行规则；
• 规则监听（Rule Listener）：监听规则的执行情况；
• 规则引擎监听（Rule Engine Listener）：监听规则引擎的执行情况；

事例

定义规则

注解方式定义规则：

@Rule(name = "weather rule", description = "if it rains then take an umbrella" )
public class WeatherRule {
    @Condition
    public boolean itRains(@Fact("rain") boolean rain) {
        return rain;
    }
    
    @Action
    public void takeAnUmbrella() {
        System.out.println("It rains, take an umbrella!");
    }
}

流式编程方式定义规则：

Rule weatherRule = new RuleBuilder()
    .name("weather rule")
    .description("if it rains then take an umbrella")
    .when(facts -> facts.get("rain").equals(true))
    .then(facts -> System.out.println("It rains, take an umbrella!"))
    .build();

表达式方式定义规则：

Rule weatherRule = new MVELRule()
    .name("weather rule")
    .description("if it rains then take an umbrella")
    .when("rain == true")
    .then("System.out.println(\"It rains, take an umbrella!\");");

yml文件方式定义规则：

name: "weather rule"
description: "if it rains then take an umbrella"
condition: "rain == true"
actions:
  - "System.out.println(\"It rains, take an umbrella!\");"

Rule weatherRule = MVELRuleFactory.createRuleFrom(new File("weather-rule.yml"));

执行规则：

public class Test {
    public static void main(String[] args) {
        // define facts
        Facts facts = new Facts();
        facts.put("rain", true);

        // define rules
        Rule weatherRule = ...
        Rules rules = new Rules();
        rules.register(weatherRule);

        // fire rules on known facts
        RulesEngine rulesEngine = new DefaultRulesEngine();
        rulesEngine.fire(rules, facts);
    }
}

具体场景事例

场景说明：

假设我们有这样一个场景：

• 如果一个数字可以被5整除，则输出“fizz”；
• 如果一个数字可以被7整除，则输出“buzz”；
• 如果一个数字可以同时被5和7整除，则输出“fizzbuzz”；
• 如果一个数字不满足以上三个条件，则输出这个数字本身。

不使用规则引擎实现：

public class FizzBuzzMain {
    public static void main(String[] args) {
        for(int i = 1; i <= 100; i++) {
            if (((i % 5) == 0) && ((i % 7) == 0))
                System.out.print("fizzbuzz");
            else if ((i % 5) == 0) System.out.print("fizz");
            else if ((i % 7) == 0) System.out.print("buzz");
            else System.out.print(i);
            System.out.println();
        }
        System.out.println();
    }
}

使用Easy Rules实现：

1. 引入依赖

<dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-core</artifactId>
    <version>3.2.0</version>
</dependency>
    <dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-support</artifactId>
    <version>3.2.0</version>
</dependency>
<dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-mvel</artifactId>
    <version>3.2.0</version>
</dependency>

2. 使用注解方式定义规则：

2.1 定义规则：

public class RuleClass {
    @Rule(priority = 1)
    public static class FizzRule {
        @Condition
        public boolean isFizz(@Fact("number") int number) {
            return number % 5 == 0;
        }
        @Action
        public void printFizz() {
            System.out.print("fizz");
        }
    }

    @Rule(priority = 2)
    public static class BuzzRule {
        @Condition
        public boolean isBuzz(@Fact("number") int number) {
            return number % 7 == 0;
        }
        @Action
        public void printBuzz() {
            System.out.print("buzz");
        }
    }

    public static class FizzBuzzRule extends UnitRuleGroup {
        public FizzBuzzRule(Object... rules) {
            for (Object rule : rules) {
                addRule(rule);
            }
        }
        @Override
        public int getPriority() {
            return 0;
        }
    }

    @Rule(priority = 3)
    public static class NonFizzBuzzRule {
        @Condition
        public boolean isNotFizzNorBuzz(@Fact("number") int number) {
            return number % 5 != 0 || number % 7 != 0;
        }
        @Action
        public void printInput(@Fact("number") int number) {
            System.out.print(number);
        }
    }
}

2.2 客户端调用：

public class FizzBuzzMainWithRule {
    public static void main(String[] args) {
        // create a rules engine
        RulesEngineParameters parameters = new RulesEngineParameters().skipOnFirstAppliedRule(true);
        RulesEngine fizzBuzzEngine = new DefaultRulesEngine(parameters);
        // create rules
        Rules rules = new Rules();
        rules.register(new FizzRule());
        rules.register(new BuzzRule());
        rules.register(new FizzBuzzRule(new FizzRule(), new BuzzRule()));
        rules.register(new NonFizzBuzzRule());
        // fire rules
        Facts facts = new Facts();
        for (int i = 1; i <= 100; i++) {
            facts.put("number", i);
            fizzBuzzEngine.fire(rules, facts);
            System.out.println();
        }
    }
}

3. 使用yml文件定义规则：

3.1 定义规则：

---
name: "fizz rule"
description: "print fizz if the number is multiple of 5"
priority: 1
condition: "number % 5 == 0"
actions:
- "System.out.println(\"fizz\")"

---
name: "buzz rule"
description: "print buzz if the number is multiple of 7"
priority: 2
condition: "number % 7 == 0"
actions:
- "System.out.println(\"buzz\")"

---
name: "fizzbuzz rule"
description: "print fizzbuzz if the number is multiple of 5 and 7"
priority: 0
condition: "number % 5 == 0 && number % 7 == 0"
actions:
- "System.out.println(\"fizzbuzz\")"

---
name: "non fizzbuzz rule"
description: "print the number itself otherwise"
priority: 3
condition: "number % 5 != 0 || number % 7 != 0"
actions:
- "System.out.println(number)"

3.2 客户端调用：

public class FizzBuzzMainWithYmlRule {
    public static void main(String[] args) throws FileNotFoundException {
        // create a rules engine
        RulesEngineParameters parameters = new RulesEngineParameters().skipOnFirstAppliedRule(true);
        RulesEngine fizzBuzzEngine = new DefaultRulesEngine(parameters);
        // create rules
        String filePath = System.getProperty("user.dir") + "/src/main/resources/easyrules/fizzbuzz/rule.yml";
        Rules rules = MVELRuleFactory.createRulesFrom(new FileReader(filePath));
        // fire rules
        Facts facts = new Facts();
        for (int i = 1; i <= 100; i++) {
            facts.put("number", i);
            fizzBuzzEngine.fire(rules, facts);
            System.out.println();
        }
    }
}

更多事例

• Easy Rules官方wiki

参考

• Easy Rules官方文档