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java easy-rules java轻量级规则引擎easy-rules使用介绍

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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

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:

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));
  }
}

执行结果如下:

本篇主要介绍easy-rules的使用

深入了解原理,可以查看github源码:https://github.com/j-easy/easy-rules

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