规则引擎入门

关于规则引擎，我们在工作中应该会经常遇到，例如我们对不同的用户给不同的折扣。前一段时间在网上闲逛，发现一个很简单的规则引擎，一下是学习笔记。

在使用之前，我们要先导入 jar 包：

<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>

一. 使用零配置的方式：

1. 规则引擎入口：

package cn.bridgeli.demo.rule;

import org.jeasy.rules.api.Facts;  
import org.jeasy.rules.api.Rules;  
import org.jeasy.rules.api.RulesEngine;  
import org.jeasy.rules.core.DefaultRulesEngine;  
import org.jeasy.rules.core.RulesEngineParameters;  
import org.junit.Test;

/**  
* @author bridgeli  
*/  
public class ThreeEightRuleTest {

@Test  
public void testRule() {  
/**  
* 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();  
}  
}  
}

这个是判断 1- 50 里面，哪些是 3 的倍数、哪些是 8 的倍数、哪些是 3 和 8 的倍数。

2. 各种规则的实现：

package cn.bridgeli.demo.rule;

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

/**  
* @author bridgeli  
*/  
@Rule(name = "被8整除")  
public class EightRule {

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

@Action  
public void eightAction(@Fact("number") int number) {  
System.out.print(number + " is eight");  
}

@Priority  
public int getPriority() {  
return 2;  
}  
}

package cn.bridgeli.demo.rule;

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

/**  
* @author bridgeli  
*/  
@Rule(name = "被3整除", description = "number如果被3整除，打印：number is three")  
public class ThreeRule {  
/**  
* 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;  
}

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

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

package cn.bridgeli.demo.rule;

import org.jeasy.rules.annotation.Rule;  
import org.jeasy.rules.support.UnitRuleGroup;

/**  
* @author bridgeli  
*/  
@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;  
}  
}

package cn.bridgeli.demo.rule;

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

/**  
* @author bridgeli  
*/  
@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;  
}  
}

二. MVEL 的方式

除了上面的方式我们还可以通过 MVEL 的方式实现。我们首先也是看入口

1. 规则入口：

package cn.bridgeli.demo.rule;

import org.jeasy.rules.api.Facts;  
import org.jeasy.rules.api.Rule;  
import org.jeasy.rules.api.Rules;  
import org.jeasy.rules.api.RulesEngine;  
import org.jeasy.rules.core.DefaultRulesEngine;  
import org.jeasy.rules.mvel.MVELRule;  
import org.jeasy.rules.mvel.MVELRuleFactory;  
import org.jeasy.rules.support.YamlRuleDefinitionReader;  
import org.junit.Test;

import java.io.FileReader;

/**  
* @author bridgeli  
*/  
public class ShopTest {

@Test  
public void testMvel() throws Exception {

//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); System.out.println(\"Shop: OK, you are allowed to buy alcohol\");");  
//创建规则2  
MVELRuleFactory ruleFactory = new MVELRuleFactory(new YamlRuleDefinitionReader());  
Rule alcoholRule = ruleFactory.createRule(new FileReader("src/main/resources/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?");

//创建一个Person实例(Fact)  
Person person = new Person();  
person.setName("Tom");  
// person.setAge(20);  
person.setAge(18);  
Facts facts = new Facts();  
facts.put("person", person);

rulesEngine.fire(rules, facts);  
}  
}

这个是根据年龄判断是一个人是否可以在超市买酒的判断。

2. yml 配置文件

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\");"

这里面需要一个 person 对象，其实很简单

3. person 对象

package cn.bridgeli.demo.rule;

import lombok.Data;

/**  
* @author bridgeli  
*/  
@Data  
public class Person {  
private String name;

private boolean adult;

private int age;  
}

简单使用了一个 lombok 插件，相信大家都知道这是什么，也可以不用，使用 get、set 方法，所以不做介绍了。

通过这两个雷子，我们就可以随心所用的使用规则引擎了，消除我们代码中的各种 if、else 判断，体现了设计模式的开闭原则。

参考资料：本来是要列出来的，但是原网站挂掉了。。。