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
