Java 轻量级规则引擎easy-rules使用介绍

NickCliff 发布于21天前

轻量级规则引擎easy-rules--参考

我们在写业务代码经常遇到需要一大堆if/else,会导致代码可读性大大降低,有没有一种方法可以避免代码中出现大量的判断语句呢?答案是用规则引擎,但是传统的规则引擎都比较重,比如开源的Drools,不适合在小需求中应用。最近在github上面看到一个傻瓜式的Java规则引擎Easy-Rules,这里结合自己写的demo介绍如何使用这个规则引擎,希望对大家有所帮助。

easy-rules的特点

  • 轻量级类库和容易上手
  • 基于POJO的开发与注解的编程模型
  • 基于MVEL表达式的编程模型(适用于极简单的规则,一般不推荐)
  • 支持根据简单的规则创建组合规则
  • 方便且适用于java的抽象的业务模型规则

它主要包括几个主要的类或接口:Rule,RulesEngine,RuleListener,Facts还有几个主要的注解:@Action,@Condition,@Fact,@Priority,@Rule

例1:基于POJO开发与注解的编程模型:判断1-50中,被3或者8整除的数

  • 首先maven 引入easy-rules
      <dependency>
            <groupId>org.jeasy</groupId>
            <artifactId>easy-rules-core</artifactId>
            <version>3.3.0</version>
        </dependency>
        <dependency>
            <groupId>org.jeasy</groupId>
            <artifactId>easy-rules-mvel</artifactId>
            <version>3.3.0</version>
        </dependency>
  • 编写规则POJO:

规则1

@Rule(name = "被3整除", description = "number如果被3整除,打印:number is three")
public class ThreeRule {
    /**
     * Condition:条件判断注解:如果return true, 执行Action
     *
     * @param number
     * @return
     */
    @Condition
    public boolean isThree(@Fact("number") int number) {
        return number % 3 == 0;
    }

    /**
     * Action 执行方法注解
     *
     * @param number
     */
    @Action
    public void threeAction(@Fact("number") int number) {
        System.out.println(number + " is three");
    }

    /**
     * Priority:优先级注解:return 数值越小,优先级越高
     *
     * @return
     */
    @Priority
    public int getPriority() {
        return 1;
    }
}

规则2

@Rule(name = "被8整除")
public class EightRule {

    /**
     * 条件
     *
     * @param number
     * @return
     */
    @Condition
    public boolean isEight(@Fact("number") int number) {
        return number % 8 == 0;
    }

    /**
     * 满足条件的动作
     *
     * @param number
     */
    @Action
    public void eightAction(@Fact("number") int number) {
        System.out.println(number + " is eight");
    }

    /**
     * 条件判断的优先级
     *
     * @return
     */
    @Priority
    public int getPriority() {
        return 2;
    }
}

规则3(组合规则-同时执行)

@Rule(name = "被3和8同时整除", description = "这是一个组合规则")
public class ThreeEightRuleUnitGroup extends UnitRuleGroup {

    public ThreeEightRuleUnitGroup(Object... rules) {
        for (Object rule : rules) {
            addRule(rule);
        }
    }

    @Override
    public int getPriority() {
        return 0;
    }

}

规则4

@Rule(name = "既不被3整除也不被8整除", description = "打印number自己")
public class OtherRule {  
    @Condition
    public boolean isOther(@Fact("number") int number){
        return number % 3 != 0 || number % 8 != 0;
    }

    @Action
    public void printSelf(@Fact("number") int number){
        System.out.print(number);
    }

    @Priority
    public int getPriority(){
        return 3;
    }
}
  • 执行规则
public class ThreeEightRuleLauncher {

    public static void main(String[] args) {
        /**
         * 创建规则执行引擎
         * 注意: skipOnFirstAppliedRule意思是,只要匹配到第一条规则就跳过后面规则匹配
         */
        RulesEngineParameters parameters = new 
        RulesEngineParameters().skipOnFirstAppliedRule(true);
        RulesEngine rulesEngine = new DefaultRulesEngine(parameters);
        //创建规则
        Rules rules = new Rules();
        rules.register(new EightRule());
        rules.register(new ThreeRule());
        rules.register(new ThreeEightRuleUnitGroup(new EightRule(), new ThreeRule()));
        rules.register(new OtherRule());
        Facts facts = new Facts();
        for (int i=1 ; i<=50 ; i++){
            //规则因素,对应的name,要和规则里面的@Fact 一致
            facts.put("number", i);
            //执行规则
            rulesEngine.fire(rules, facts);
            System.out.println();
        }
    }
}

例2:基于MVEL表达式的编程模型

本例演示如何使用MVEL表达式定义规则,MVEL通过Easy-Rules MVEL模块提供。此模块包含使用MVEL定义规则的API。我们将在这里使用这些API,其目标是实现一个简单的商店应用程序,要求如下:禁止儿童购买酒精,成年人的最低法定年龄为18岁。 商店顾客由Person类定义:

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Person {
    private String name;

    private boolean adult;

    private int age;
    //getter, setter 省略


    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

我们定义两个规则:

  • 规则1:可以更新Person实例,判断年龄是否大于18岁,并设置成人标志。
  • 规则2:判断此人是否为成年人,并拒绝儿童(即非成年人)购买酒精。

显然,规则1的优先级要大于规则2,我们可以设置规则1的Priority为1,规则2的Priority为2,这样保证规则引擎在执行规则的时候,按优先级的顺序执行规则。

规则1的定义

 Rule ageRule = new MVELRule()
                .name("age rule")
                .description("Check if person's age is > 18 and marks the person as adult")
                .priority(1)
                .when("person.age > 18")
                .then("person.setAdult(true);");

规则2的定义,我们放到alcohol-rule.yml文件中

name: "alcohol rule"  
description: "children are not allowed to buy alcohol"  
priority: 2  
condition: "person.isAdult() == false"  
actions:  
  - "System.out.println(\"Shop: Sorry, you are not allowed to buy alcohol\");"
  • 执行规则
public class ShopLauncher {
    public static void main(String[] args) throws Exception {
        //创建一个Person实例(Fact)
        Person tom = new Person("Tom", 19);
        Facts facts = new Facts();
        facts.put("person", tom);

        //创建规则1
        Rule ageRule = new MVELRule()
                .name("age rule")
                .description("Check if person's age is > 18 and marks the person as adult")
                .priority(1)
                .when("person.age > 18")
                .then("person.setAdult(true);");
        //创建规则2
        Rule alcoholRule = new MVELRuleFactory(new YamlRuleDefinitionReader()).
                createRule(new FileReader(ResourceUtils.getFile("classpath:alcohol-rule.yml")));

        Rules rules = new Rules();
        rules.register(ageRule);
        rules.register(alcoholRule);

        //创建规则执行引擎,并执行规则
        RulesEngine rulesEngine = new DefaultRulesEngine();
        System.out.println("Tom: Hi! can I have some Vodka please?");
        rulesEngine.fire(rules, facts);
        System.out.println(JSON.toJSONString(tom));
    }
}
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