规则引擎的目的是以松散灵活的方式来替代硬编码式的if else判断，来达到解耦的目的
easy-rules
easy-rules是个轻量级的规则引擎库，提供了注解等多种配置方式
使用实例
（1）如果一个数字可以被5整除，则输出是5的倍数；
（2）如果一个数字可以被8整除，则输出是8的倍数”；
（3）如果一个数字可以同时被5和8整除，则输出是5的倍数 是8的倍数；
（4）如果一个数字不满足以上三个条件，则输出这个数字本身
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| <dependency>
<groupId>org.jeasy</groupId>
<artifactId>easy-rules-core</artifactId>
<version>3.2.0</version>
</dependency>
<dependency>
<groupId>org.jeasy</groupId>
<artifactId>easy-rules-support</artifactId>
<version>3.2.0</version>
</dependency>
<dependency>
<groupId>org.jeasy</groupId>
<artifactId>easy-rules-mvel</artifactId>
<version>3.2.0</version>
</dependency>
|
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|
public class RuleClass {
public static class FiveAndEightMultipleRule extends UnitRuleGroup {
public FiveAndEightMultipleRule(Object... rules) {
for(Object rule : rules){
addRule(rule);
}
}
@Override
public int getPriority() {
return 0;
}
}
@Rule(priority = 1)
public static class FiveMultipleRule{
@Condition
public boolean isFiveMultiple(@Fact("number") Integer number){
return number % 5 == 0;
}
@Action
public void print(@Fact("number") Integer number){
System.out.println(number + " is 5 Multiple");
}
}
@Rule(priority = 2)
public static class EightMultipleRule{
@Condition
public boolean isEightMultiple(@Fact("number") Integer number){
return number % 8 == 0;
}
@Action
public void print(@Fact("number") Integer number){
System.out.println(number + " is 8 Multiple");
}
}
@Rule(priority = 3)
public static class NoneFiveAndEightMultipleRule{
@Condition
public boolean isNoneFiveAndEightMultiple(@Fact("number") Integer number){
return number % 5 != 0 && number % 8 != 0;
}
@Action
public void print(@Fact("number") Integer number){
System.out.println(number);
}
}
}
|
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| public class RuleClient {
public static void main(String[] args) {
RulesEngineParameters parameters = new RulesEngineParameters().skipOnFirstAppliedRule(true);
RulesEngine rulesEngine = new DefaultRulesEngine(parameters);
Rules rules = new Rules();
rules.register(new RuleClass.FiveAndEightMultipleRule(new RuleClass.FiveMultipleRule(), new RuleClass.EightMultipleRule()));
rules.register(new RuleClass.FiveMultipleRule());
rules.register(new RuleClass.EightMultipleRule());
rules.register(new RuleClass.NoneFiveAndEightMultipleRule());
Facts facts = new Facts();
for(int i=1; i<=100; i++){
facts.put("number", i);
rulesEngine.fire(rules, facts);
}
}
}
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@Rule定义规则，priority设置规则的优先级，@Condition规则触发的条件，@Action标注的方法触发的动作，Facts的用法很像Map，可将其作为参数传入@Condition和@Action标注的方法
原理
可以观察下注册规则时rules的register方法
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| rules.register(new RuleClass.FiveAndEightMultipleRule(new RuleClass.FiveMultipleRule(), new RuleClass.EightMultipleRule()));
rules.register(new RuleClass.FiveMultipleRule());
rules.register(new RuleClass.EightMultipleRule());
rules.register(new RuleClass.NoneFiveAndEightMultipleRule());
|
其源码
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| public void register(Object rule) {
Objects.requireNonNull(rule);
this.rules.add(RuleProxy.asRule(rule));
}
public static Rule asRule(Object rule) {
Rule result;
if (rule instanceof Rule) {
result = (Rule)rule;
} else {
ruleDefinitionValidator.validateRuleDefinition(rule);
result = (Rule)Proxy.newProxyInstance(Rule.class.getClassLoader(), new Class[]{Rule.class, Comparable.class}, new RuleProxy(rule));
}
return result;
}
|
可以看到，如果有实现Rule接口，则直接返回，没有的话(即基于注解的形式)，则利用JDK的动态代理进行包装
easy-rules还提供了通过配置文件来定义规则，这里不再描述