规则引擎-easy rules

easy rules

easy rules is a Java rules engine inspired by an article called “Should I use a Rules Engine?” of Martin Fowler in which Martin says:

You can build a simple rules engine yourself. All you need is to create a bunch of objects with conditions and actions, store them in a collection, and run through them to evaluate the conditions and execute the actions.

这正是Easy Rules所做的，它提供Rule抽象以创建具有条件和动作的规则，并提供RuleEngine API，该API通过一组规则运行以评估条件并执行动作。

核心特性

轻量级库和易于学习的API
基于POJO的开发与注释编程模型
有用的抽象定义业务规则并通过Java轻松应用
从原始规则创建复合规则的能力
使用表达式语言（如MVEL和SpEL）定义规则的能力

ps: 个人感觉比如 drools，这个设计更加符合我的口味。

快速入门

maven 引入

[xml]

<dependency>
	<groupId>org.jeasy</groupId>
	<artifactId>easy-rules-core</artifactId>
	<version>3.1.0</version>
</dependency>
<dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-mvel</artifactId>
    <version>3.1.0</version>
</dependency>

定义你的规则

注解式

[java]

@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!");
    }
}

声明式

[java]

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();

使用 EL 表达式

[java]

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!\");");

使用规则描述符

类似于 weather-rule.yml 的写法： [yml]

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

使用

[java]

MVELRuleFactory ruleFactory = new MVELRuleFactory(new YamlRuleDefinitionReader());
Rule weatherRule = ruleFactory.createRule(new FileReader("weather-rule.yml"));

触发

[java]

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);
}

原文链接：https://houbb.github.io/2020/05/26/rule-engine-02-easy-rules

规则引擎-easy rules插图