规则引擎架构-基于easy-rules

概念理解

描述一个简单的处理：基于一堆现实情况，运用规则引擎、经过处理得到对应的结果，然后再据此做后续的事情。

• fact: 事实，已有的现实情况，即输入信息
• rules: 规则集合，由一系列规则组成，可能有不同的规则排列
• rule: 规则，包含基本的判断条件和条件符合要做的动作。
• condition: 规则的判定条件（特定的判断逻辑 if else）
• action: 规则判定符合后执行的动作
  

实例和编码

一句话描述： 人提着包去酒店买酒，需要判断是否成年人，成年人才能购买酒，商店据此卖你酒，你买到了酒就装包里走人，回家喝酒去。

接下来看easy-rules的定义和处理。

抽象出2条规则

@Rule(name = "age-rule", description = "age-rule", priority = 1)
public class AgeRule {

    @Condition
    public boolean isAdult(@Fact("person") Person person) {
        return person.getAge() > 18;
    }

    @Action
    public void setAdult(@Fact("person") Person person) {
        person.setAdult(true);
    }
}

package org.jeasy.rules.tutorials.shop;

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

/**
 * @author dingqi on 2023/5/26
 * @since 1.0.0
 */
@Rule(name = "alcohol-rule", description = "alcohol-rule", priority = 2)
public class AlcoholRule {

    @Condition
    public boolean shopRule(@Fact("person") Person person) {
        return person.isAdult() == true;
    }

    @Action
    public void shopReply(@Fact("bag") Bag bag) {
        bag.setSuccess(true);
        bag.add("Vodka");
    }
}

简单的规则引擎

// create a rule set
Rules rules = new Rules();
rules.register(new AgeRule());
rules.register(new AlcoholRule());

//create a default rules engine and fire rules on known facts
DefaultRulesEngine rulesEngine = new DefaultRulesEngine();

事实1的处理

Facts facts = new Facts();
Person tom = new Person("Tom", 19);
facts.put("person", tom);
Bag bag = new Bag();
facts.put("bag", bag);

System.out.println("Tom: Hi! can I have some Vodka please?");
rulesEngine.fire(rules, facts);
System.out.println("Tom: bag is " + bag);

输出：Tom成年了，买到了伏特加

Tom: Hi! can I have some Vodka please?
Tom: bag is Bag{success=true, goods=[Vodka]}

事实2的处理

Person jack = new Person("Jack", 10);
facts.put("person", jack);
Bag bag2 = new Bag();
facts.put("bag", bag2);

System.out.println("Jack: Hi! can I have some Vodka please?");
rulesEngine.fire(rules, facts);
System.out.println("Jack: bag is " + bag2);

输出：Jack未成年，无功而返

Jack: Hi! can I have some Vodka please?
Jack: bag is Bag{success=false, goods=[]}

easy-rules 规则的抽象和执行

事实描述

public class Facts implements Iterable<Fact<?>> {

    private final Set<Fact<?>> facts = new HashSet<>();

/**
 * A class representing a named fact. Facts have unique names within a {@link Facts}
 * instance.
 * 
 * @param  type of the fact
 * @author Mahmoud Ben Hassine
 */
public class Fact<T> {
	
	private final String name;
	private final T value;

事实简单就是key、value对， 某个事实的名称，和事实的属性特征（以一切皆对象来看，就是一个一个的对象组成了事实）。（只要在规则条件真正执行前，能明确这些事实就行）

规则的抽象

• 名称
• 描述
• 优先级
• 执行Facts的的方法

见org.jeasy.rules.api.Rule接口 和基础实现类org.jeasy.rules.core.BasicRule

条件和动作注解：

@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Condition {

}

@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Condition {

}

默认的规则

class DefaultRule extends BasicRule {

    private final Condition condition;
    private final List<Action> actions;

    DefaultRule(String name, String description, int priority, Condition condition, List<Action> actions) {
        super(name, description, priority);
        this.condition = condition;
        this.actions = actions;
    }

    @Override
    public boolean evaluate(Facts facts) {
        return condition.evaluate(facts);
    }

    @Override
    public void execute(Facts facts) throws Exception {
        for (Action action : actions) {
            action.execute(facts);
        }
    }

}

动态代理执行规则和动作

使用org.jeasy.rules.api.Rules添加规则时如下：

• org.jeasy.rules.api.Rules#register

 public void register(Object... rules) {
     Objects.requireNonNull(rules);
     for (Object rule : rules) {
         Objects.requireNonNull(rule);
         this.rules.add(RuleProxy.asRule(rule));
     }
 }

使用org.jeasy.rules.annotation.Rule注解构造的规则是使用RuleProxy构造的

规则的执行：org.jeasy.rules.core.DefaultRulesEngine#doFire

void doFire(Rules rules, Facts facts) {
    if (rules.isEmpty()) {
        LOGGER.warn("No rules registered! Nothing to apply");
        return;
    }
    logEngineParameters();
    log(rules);
    log(facts);
    LOGGER.debug("Rules evaluation started");
    for (Rule rule : rules) {
        final String name = rule.getName();
        final int priority = rule.getPriority();
        if (priority > parameters.getPriorityThreshold()) {
            LOGGER.debug("Rule priority threshold ({}) exceeded at rule '{}' with priority={}, next rules will be skipped",
                    parameters.getPriorityThreshold(), name, priority);
            break;
        }
        if (!shouldBeEvaluated(rule, facts)) {
            LOGGER.debug("Rule '{}' has been skipped before being evaluated", name);
            continue;
        }
        boolean evaluationResult = false;
        try {
            evaluationResult = rule.evaluate(facts);
        } catch (RuntimeException exception) {
            LOGGER.error("Rule '" + name + "' evaluated with error", exception);
            triggerListenersOnEvaluationError(rule, facts, exception);
            // give the option to either skip next rules on evaluation error or continue by considering the evaluation error as false
            if (parameters.isSkipOnFirstNonTriggeredRule()) {
                LOGGER.debug("Next rules will be skipped since parameter skipOnFirstNonTriggeredRule is set");
                break;
            }
        }
        if (evaluationResult) {
            LOGGER.debug("Rule '{}' triggered", name);
            triggerListenersAfterEvaluate(rule, facts, true);
            try {
                triggerListenersBeforeExecute(rule, facts);
                rule.execute(facts);
                LOGGER.debug("Rule '{}' performed successfully", name);
                triggerListenersOnSuccess(rule, facts);
                if (parameters.isSkipOnFirstAppliedRule()) {
                    LOGGER.debug("Next rules will be skipped since parameter skipOnFirstAppliedRule is set");
                    break;
                }
            } catch (Exception exception) {
                LOGGER.error("Rule '" + name + "' performed with error", exception);
                triggerListenersOnFailure(rule, exception, facts);
                if (parameters.isSkipOnFirstFailedRule()) {
                    LOGGER.debug("Next rules will be skipped since parameter skipOnFirstFailedRule is set");
                    break;
                }
            }
        } else {
            LOGGER.debug("Rule '{}' has been evaluated to false, it has not been executed", name);
            triggerListenersAfterEvaluate(rule, facts, false);
            if (parameters.isSkipOnFirstNonTriggeredRule()) {
                LOGGER.debug("Next rules will be skipped since parameter skipOnFirstNonTriggeredRule is set");
                break;
            }
        }
    }
}

默认的规则引擎直接遍历规则去执行，如果condition执行命中后，则去执行action

public class RuleProxy implements InvocationHandler

private Object evaluateMethod(final Object[] args) throws IllegalAccessException, InvocationTargetException {
    Facts facts = (Facts) args[0];
    Method conditionMethod = getConditionMethod();
    try {
        List<Object> actualParameters = getActualParameters(conditionMethod, facts);
        return conditionMethod.invoke(target, actualParameters.toArray()); // validated upfront
    } catch (NoSuchFactException e) {
        LOGGER.warn("Rule '{}' has been evaluated to false due to a declared but missing fact '{}' in {}",
                getTargetClass().getName(), e.getMissingFact(), facts);
        return false;
    } catch (IllegalArgumentException e) {
        LOGGER.warn("Types of injected facts in method '{}' in rule '{}' do not match parameters types",
                conditionMethod.getName(), getTargetClass().getName(), e);
        return false;
    }
}

规则执行监听器

在规则执行的过程中，可以做各种操作。可以看成规则的扩展点

/**
 * A listener for rule execution events.
 *
 * @author Mahmoud Ben Hassine ([email protected])
 */
public interface RuleListener {

    /**
     * Triggered before the evaluation of a rule.
     *
     * @param rule being evaluated
     * @param facts known before evaluating the rule
     * @return true if the rule should be evaluated, false otherwise
     */
    default boolean beforeEvaluate(Rule rule, Facts facts) {
        return true;
    }

    /**
     * Triggered after the evaluation of a rule.
     *
     * @param rule that has been evaluated
     * @param facts known after evaluating the rule
     * @param evaluationResult true if the rule evaluated to true, false otherwise
     */
    default void afterEvaluate(Rule rule, Facts facts, boolean evaluationResult) { }

    /**
     * Triggered on condition evaluation error due to any runtime exception.
     *
     * @param rule that has been evaluated
     * @param facts known while evaluating the rule
     * @param exception that happened while attempting to evaluate the condition.
     */
    default void onEvaluationError(Rule rule, Facts facts, Exception exception) { }

    /**
     * Triggered before the execution of a rule.
     *
     * @param rule the current rule
     * @param facts known facts before executing the rule
     */
    default void beforeExecute(Rule rule, Facts facts) { }

    /**
     * Triggered after a rule has been executed successfully.
     *
     * @param rule the current rule
     * @param facts known facts after executing the rule
     */
    default void onSuccess(Rule rule, Facts facts) { }

    /**
     * Triggered after a rule has failed.
     *
     * @param rule the current rule
     * @param facts known facts after executing the rule
     * @param exception the exception thrown when attempting to execute the rule
     */
    default void onFailure(Rule rule, Facts facts, Exception exception) { }

}

回顾规则执行和监听器的执行过程

// 1. 条件执行前
triggerListenersBeforeEvaluate(rule, facts);
try {
	evaluationResult = rule.evaluate(facts);
} catch(Exception e){
	 // 2. 条件执行失败
	 triggerListenersOnEvaluationError(rule, facts, exception);
}

if (evaluationResult) {
	// 3. 条件执行后（条件满足）
	triggerListenersAfterEvaluate(rule, facts, true);
	 try {
	 	  // 4. 动作执行前
	 	  triggerListenersBeforeExecute(rule, facts);
          rule.execute(facts);
          // 5. 动作执行后
          triggerListenersOnSuccess(rule, facts);
	 } catch (Exception exception) {
	 	 // 6. 条件执行失败
	 	 triggerListenersOnFailure(rule, exception, facts);
	 }
}else{
	// 3. 条件执行后（条件不满足）
	triggerListenersAfterEvaluate(rule, facts, false);
}

扩展

1. Java Expression Language (JEXL) ：表达式语言引擎

https://commons.apache.org/proper/commons-jexl/apidocs/org/apache/commons/jexl3/JexlEngine.html

2. MVEL：一个功能强大的基于Java应用程序的表达式语言。

3. SpEL：Spring表达式语言

name: adult rule
description: when age is greater than 18, then mark as adult
priority: 1
condition: "#{ ['person'].age > 18 }"
actions:
  - "#{ ['person'].setAdult(true) }"