合理的使用规则引擎可以极大的减少代码复杂度，提升代码可维护性。业界知名的开源规则引擎有Drools，功能丰富，但也比较庞大。在一些简单的场景中，我们只需要简易的规则引擎就能满足要求。
本文介绍一个小巧的规则引擎 easy-rules，作为一个lib库提供，支持spring的SPEL表达式，可以很好的集成在spring项目中。
具体的代码参照 示例项目 https://github.com/qihaiyan/springcamp/tree/master/spring-easy-rule
一、概述
通过将业务规则配置的配置文件中，可以精简代码，同时已于维护，当规则修改时，只需要修改配置文件即可。easy-rules是一个小巧的规则引擎，支持spring的SPEL表达式，同时还支持 Apache JEXL 表达式和 MVL 表达式。
二、项目中加入依赖
在项目的gradle中增加依赖关系。
build.gradle:
plugins {
id 'org.springframework.boot' version '3.0.5'
id 'io.spring.dependency-management' version '1.1.0'
id 'java'
}
group = 'cn.springcamp'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
configurations {
compileOnly {
extendsFrom annotationProcessor
}
testCompileOnly {
extendsFrom testAnnotationProcessor
}
}
repositories {
mavenCentral()
}
dependencies {
implementation "org.springframework.boot:spring-boot-starter-json"
implementation 'org.springframework.boot:spring-boot-starter-validation'
implementation 'org.jeasy:easy-rules-core:4.1.0'
implementation 'org.jeasy:easy-rules-spel:4.1.0'
implementation 'org.jeasy:easy-rules-support:4.1.0'
annotationProcessor 'org.projectlombok:lombok'
testAnnotationProcessor 'org.projectlombok:lombok'
testImplementation "org.springframework.boot:spring-boot-starter-test"
testImplementation 'org.junit.vintage:junit-vintage-engine'
testImplementation 'org.junit.vintage:junit-vintage-engine'
}
dependencyManagement {
imports {
mavenBom "org.springframework.cloud:spring-cloud-dependencies:2022.0.1"
}
}
test {
useJUnitPlatform()
}
三、配置文件
示例程序将业务规则放到配置文件中，业务规则配置文件(demo-rule.yml)代码:
name: "age rule"
description: ""
priority: 1
condition: "#person.getAdult() == false"
actions:
- "T(java.lang.System).out.println(\"Shop: Sorry, you are not allowed to buy alcohol\")"
- "#person.setAdult(true)"
- "#person.setAge(18)"
---
name: "alcohol rule"
description: ""
priority: 1
condition: "#person.getAdult() == true"
actions:
- "T(java.lang.System).out.println(\"Shop: you are now allowed to buy alcohol\")"
配置文件中的规则通过 condition 进行配置，当满足规则时，会调用 actions 中配置的动作。
示例项目使用了spring的SPEL表达式进行规则配置，配置文件中配置了2个规则，第一个规则通过 person这个spring bean中的getAdult()判断是否满足规则，满足规则时调用三个方法。
在spring-boot本身的配置文件中 application.yml 配置规则文件：
rule:
skip-on-first-failed-rule: true
skip-on-first-applied-rule: false
skip-on-first-non-triggered-rule: true
rules:
- rule-id: "demo"
rule-file-location: "classpath:demo-rule.yml"
四、代码中对规则引擎进行配置
通过 RuleEngineConfig这个spring的配置类对规则引擎进行配置：
@Slf4j
@EnableConfigurationProperties(RuleEngineConfigProperties.class)
@Configuration
public class RuleEngineConfig implements BeanFactoryAware {
@Autowired(required = false)
private List<RuleListener> ruleListeners;
@Autowired(required = false)
private List<RulesEngineListener> rulesEngineListeners;
private BeanFactory beanFactory;
@Bean
public RulesEngineParameters rulesEngineParameters(RuleEngineConfigProperties properties) {
RulesEngineParameters parameters = new RulesEngineParameters();
parameters.setSkipOnFirstAppliedRule(properties.isSkipOnFirstAppliedRule());
parameters.setSkipOnFirstFailedRule(properties.isSkipOnFirstFailedRule());
parameters.setSkipOnFirstNonTriggeredRule(properties.isSkipOnFirstNonTriggeredRule());
return parameters;
}
@Bean
public RulesEngine rulesEngine(RulesEngineParameters rulesEngineParameters) {
DefaultRulesEngine rulesEngine = new DefaultRulesEngine(rulesEngineParameters);
if (!CollectionUtils.isEmpty(ruleListeners)) {
rulesEngine.registerRuleListeners(ruleListeners);
}
if (!CollectionUtils.isEmpty(rulesEngineListeners)) {
rulesEngine.registerRulesEngineListeners(rulesEngineListeners);
}
return rulesEngine;
}
@Bean
public BeanResolver beanResolver() {
return new BeanFactoryResolver(beanFactory);
}
@Bean
public RuleEngineTemplate ruleEngineTemplate(RuleEngineConfigProperties properties, RulesEngine rulesEngine) {
RuleEngineTemplate ruleEngineTemplate = new RuleEngineTemplate();
ruleEngineTemplate.setBeanResolver(beanResolver());
ruleEngineTemplate.setProperties(properties);
ruleEngineTemplate.setRulesEngine(rulesEngine);
return ruleEngineTemplate;
}
@Bean
public RuleListener defaultRuleListener() {
return new RuleListener() {
@Override
public boolean beforeEvaluate(Rule rule, Facts facts) {
return true;
}
@Override
public void afterEvaluate(Rule rule, Facts facts, boolean b) {
log.info("-----------------afterEvaluate-----------------");
log.info(rule.getName() + rule.getDescription() + facts.toString());
}
@Override
public void beforeExecute(Rule rule, Facts facts) {
log.info("-----------------beforeExecute-----------------");
log.info(rule.getName() + rule.getDescription() + facts.toString());
}
@Override
public void onSuccess(Rule rule, Facts facts) {
log.info("-----------------onSuccess-----------------");
log.info(rule.getName() + rule.getDescription() + facts.toString());
}
@Override
public void onFailure(Rule rule, Facts facts, Exception e) {
log.info("-----------------onFailure-----------------");
log.info(rule.getName() + "----------" + rule.getDescription() + facts.toString() + e.toString());
}
};
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
}
配置文件中配置了 ruleEngineTemplate这个spring bean，通过ruleEngineTemplate触发规则引擎的执行。
五、执行规则引擎
ruleEngineTemplate配置好后，我们可以在业务代码中执行规则引擎，处理配置文件中配置的业务规则：
最为演示，我们将规则引擎的执行代码放到了 Application 的 run 方法中，程序启动后立即执行规则引擎：
@SpringBootApplication
public class Application implements CommandLineRunner {
@Autowired
RuleEngineTemplate ruleEngineTemplate;
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Override
public void run(String... args) {
Person person = new Person();
Facts facts = new Facts();
facts.put("person", person);
ruleEngineTemplate.fire("demo", facts);
}
}
程序执行后可以看到控制台里打印了 Shop: Sorry, you are not allowed to buy alcohol，这个内容对应的是我们在规则文件中的actions中配置的 "T(java.lang.System).out.println(\"Shop: Sorry, you are not allowed to buy alcohol\")"，说明规则成功执行了。