Java规则引擎 Easy Rules

Easy Rules简单易用,只需两步:

首先,定义规则,方式有很多种

方式一:注解

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@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!");
}

}
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方式二:链式编程

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();
方式三:表达式

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!”);”);
方式四:yml配置文件

例如:weather-rule.yml

name: “weather rule”
description: “if it rains then take an umbrella”
condition: “rain == true”
actions:

  • “System.out.println(“It rains, take an umbrella!”);”
    MVELRuleFactory ruleFactory = new MVELRuleFactory(new YamlRuleDefinitionReader());
    Rule weatherRule = ruleFactory.createRule(new FileReader(“weather-rule.yml”));
    接下来,应用规则

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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);
}

}
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入门案例:Hello Easy Rules

org.jeasy easy-rules-core 4.0.0 通过骨架创建maven项目:

mvn archetype:generate
-DarchetypeGroupId=org.jeasy
-DarchetypeArtifactId=easy-rules-archetype
-DarchetypeVersion=4.0.0
默认给我们生成了一个HelloWorldRule规则,如下:

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package com.cjs.example.rules;

import org.jeasy.rules.annotation.Action;
import org.jeasy.rules.annotation.Condition;
import org.jeasy.rules.annotation.Rule;

@Rule(name = “Hello World rule”, description = “Always say hello world”)
public class HelloWorldRule {

@Condition
public boolean when() {
    return true;
}

@Action
public void then() throws Exception {
    System.out.println("hello world");
}

}
在Easy Rules中,Rule接口代表规则

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public interface Rule {

/**
* This method encapsulates the rule's conditions.
* @return true if the rule should be applied given the provided facts, false otherwise
*/
boolean evaluate(Facts facts);

/**
* This method encapsulates the rule's actions.
* @throws Exception if an error occurs during actions performing
*/
void execute(Facts facts) throws Exception;

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

}
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evaluate方法封装了必须计算结果为TRUE才能触发规则的条件。execute方法封装了在满足规则条件时应该执行的动作。条件和操作由Condition和Action接口表示。

定义规则有两种方式:

通过在POJO类上添加注解
通过RuleBuilder API编程
可以在一个POJO类上添加@Rule注解,例如:

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@Rule(name = “my rule”, description = “my rule description”, priority = 1)
public class MyRule {

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

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

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

}
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@Condition注解指定规则条件
@Fact注解指定参数
@Action注解指定规则执行的动作

RuleBuilder支持链式风格定义规则,例如:

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Rule rule = new RuleBuilder()
.name(“myRule”)
.description(“myRuleDescription”)
.priority(3)
.when(condition)
.then(action1)
.then(action2)
.build();
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组合规则

CompositeRule由一组规则组成。这是一个典型地组合设计模式的实现。

组合规则是一个抽象概念,因为可以以不同方式触发组合规则。

Easy Rules自带三种CompositeRule实现:

UnitRuleGroup : 要么应用所有规则,要么不应用任何规则(AND逻辑)
ActivationRuleGroup : 它触发第一个适用规则,并忽略组中的其他规则(XOR逻辑)
ConditionalRuleGroup : 如果具有最高优先级的规则计算结果为true,则触发其余规则
复合规则可以从基本规则创建并注册为常规规则:

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//Create a composite rule from two primitive rules
UnitRuleGroup myUnitRuleGroup = new UnitRuleGroup(“myUnitRuleGroup”, “unit of myRule1 and myRule2”);
myUnitRuleGroup.addRule(myRule1);
myUnitRuleGroup.addRule(myRule2);

//Register the composite rule as a regular rule
Rules rules = new Rules();
rules.register(myUnitRuleGroup);

RulesEngine rulesEngine = new DefaultRulesEngine();
rulesEngine.fire(rules, someFacts);
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