1. Easy Rules 概述

Easy Rules是一個Java規(guī)則引擎，靈感來自一篇名為《Should I use a Rules Engine?》的文章

規(guī)則引擎就是提供一種可選的計算模型。與通常的命令式模型（由帶有條件和循環(huán)的命令依次組成）不同，規(guī)則引擎基于生產(chǎn)規(guī)則系統(tǒng)。這是一組生產(chǎn)規(guī)則，每條規(guī)則都有一個條件（condition）和一個動作（action）———— 簡單地說，可以將其看作是一組if-then語句。

精妙之處在于規(guī)則可以按任何順序編寫，引擎會決定何時使用對順序有意義的任何方式來計算它們。考慮它的一個好方法是系統(tǒng)運行所有規(guī)則，選擇條件成立的規(guī)則，然后執(zhí)行相應(yīng)的操作。這樣做的好處是，很多問題都很自然地符合這個模型：

if car.owner.hasCellPhone then premium += 100;if car.model.theftRating > 4 then premium += 200;if car.owner.livesInDodgyArea && car.model.theftRating > 2 then premium += 300;

規(guī)則引擎是一種工具，它使得這種計算模型編程變得更容易。它可能是一個完整的開發(fā)環(huán)境，或者一個可以在傳統(tǒng)平臺上工作的框架。生產(chǎn)規(guī)則計算模型最適合僅解決一部分計算問題，因此規(guī)則引擎可以更好地嵌入到較大的系統(tǒng)中。

你可以自己構(gòu)建一個簡單的規(guī)則引擎。你所需要做的就是創(chuàng)建一組帶有條件和動作的對象，將它們存儲在一個集合中，然后遍歷它們以評估條件并執(zhí)行這些動作。

Easy Rules它提供Rule抽象以創(chuàng)建具有條件和動作的規(guī)則，并提供RuleEngine API，該API通過一組規(guī)則運行以評估條件并執(zhí)行動作。

Easy Rules簡單易用，只需兩步：

首先，定義規(guī)則，方式有很多種

方式一：注解

@Rule(name = 'weather rule', description = 'if it rains then take an umbrella')public class WeatherRule { @Condition public boolean itRains(@Fact('rain') boolean rain) { return rain; } @Action public void takeAnUmbrella() { System.out.println('It rains, take an umbrella!'); }}

方式二：鏈?zhǔn)骄幊?/p>

Rule weatherRule = new RuleBuilder() .name('weather rule') .description('if it rains then take an umbrella') .when(facts -> facts.get('rain').equals(true)) .then(facts -> System.out.println('It rains, take an umbrella!')) .build();

方式三：表達式

Rule weatherRule = new MVELRule() .name('weather rule') .description('if it rains then take an umbrella') .when('rain == true') .then('System.out.println('It rains, take an umbrella!');');

方式四：yml配置文件

例如：weather-rule.yml

name: 'weather rule'description: 'if it rains then take an umbrella'condition: 'rain == true'actions: - 'System.out.println('It rains, take an umbrella!');'

MVELRuleFactory ruleFactory = new MVELRuleFactory(new YamlRuleDefinitionReader());Rule weatherRule = ruleFactory.createRule(new FileReader('weather-rule.yml'));

接下來，應(yīng)用規(guī)則

public class Test { public static void main(String[] args) { // define facts Facts facts = new Facts(); facts.put('rain', true); // define rules Rule weatherRule = ... Rules rules = new Rules(); rules.register(weatherRule); // fire rules on known facts RulesEngine rulesEngine = new DefaultRulesEngine(); rulesEngine.fire(rules, facts); }}

入門案例：Hello Easy Rules

<dependency> <groupId>org.jeasy</groupId> <artifactId>easy-rules-core</artifactId> <version>4.0.0</version></dependency>

通過骨架創(chuàng)建maven項目：

mvn archetype:generate -DarchetypeGroupId=org.jeasy -DarchetypeArtifactId=easy-rules-archetype -DarchetypeVersion=4.0.0

默認(rèn)給我們生成了一個HelloWorldRule規(guī)則，如下：

package com.cjs.example.rules;import org.jeasy.rules.annotation.Action;import org.jeasy.rules.annotation.Condition;import org.jeasy.rules.annotation.Rule;@Rule(name = 'Hello World rule', description = 'Always say hello world')public class HelloWorldRule { @Condition public boolean when() { return true; } @Action public void then() throws Exception { System.out.println('hello world'); }}

2. 規(guī)則定義

2.1. 定義規(guī)則

大多數(shù)業(yè)務(wù)規(guī)則可以用以下定義表示：

Name : 一個命名空間下的唯一的規(guī)則名稱 Description : 規(guī)則的簡要描述 Priority : 相對于其他規(guī)則的優(yōu)先級 Facts : 事實，可立即為要處理的數(shù)據(jù) Conditions : 為了應(yīng)用規(guī)則而必須滿足的一組條件 Actions : 當(dāng)條件滿足時執(zhí)行的一組動作

Easy Rules為每個關(guān)鍵點提供了一個抽象來定義業(yè)務(wù)規(guī)則。

在Easy Rules中，Rule接口代表規(guī)則

public interface Rule { /** * This method encapsulates the rule’s conditions. * @return true if the rule should be applied given the provided facts, false otherwise */ boolean evaluate(Facts facts); /** * This method encapsulates the rule’s actions. * @throws Exception if an error occurs during actions performing */ void execute(Facts facts) throws Exception; //Getters and setters for rule name, description and priority omitted.}

evaluate方法封裝了必須計算結(jié)果為TRUE才能觸發(fā)規(guī)則的條件。execute方法封裝了在滿足規(guī)則條件時應(yīng)該執(zhí)行的動作。條件和操作由Condition和Action接口表示。

定義規(guī)則有兩種方式：

通過在POJO類上添加注解 通過RuleBuilder API編程

可以在一個POJO類上添加@Rule注解，例如：

@Rule(name = 'my rule', description = 'my rule description', priority = 1)public class MyRule { @Condition public boolean when(@Fact('fact') fact) { //my rule conditions return true; } @Action(order = 1) public void then(Facts facts) throws Exception { //my actions } @Action(order = 2) public void finally() throws Exception { //my final actions }}

@Condition注解指定規(guī)則條件@Fact注解指定參數(shù)@Action注解指定規(guī)則執(zhí)行的動作

RuleBuilder支持鏈?zhǔn)斤L(fēng)格定義規(guī)則，例如：

Rule rule = new RuleBuilder().name('myRule').description('myRuleDescription').priority(3).when(condition).then(action1).then(action2).build();

組合規(guī)則

CompositeRule由一組規(guī)則組成。這是一個典型地組合設(shè)計模式的實現(xiàn)。

組合規(guī)則是一個抽象概念，因為可以以不同方式觸發(fā)組合規(guī)則。

Easy Rules自帶三種CompositeRule實現(xiàn)：

UnitRuleGroup : 要么應(yīng)用所有規(guī)則，要么不應(yīng)用任何規(guī)則（AND邏輯） ActivationRuleGroup : 它觸發(fā)第一個適用規(guī)則，并忽略組中的其他規(guī)則（XOR邏輯） ConditionalRuleGroup : 如果具有最高優(yōu)先級的規(guī)則計算結(jié)果為true，則觸發(fā)其余規(guī)則

復(fù)合規(guī)則可以從基本規(guī)則創(chuàng)建并注冊為常規(guī)規(guī)則：

//Create a composite rule from two primitive rulesUnitRuleGroup myUnitRuleGroup = new UnitRuleGroup('myUnitRuleGroup', 'unit of myRule1 and myRule2');myUnitRuleGroup.addRule(myRule1);myUnitRuleGroup.addRule(myRule2);//Register the composite rule as a regular ruleRules rules = new Rules();rules.register(myUnitRuleGroup);RulesEngine rulesEngine = new DefaultRulesEngine();rulesEngine.fire(rules, someFacts);

每個規(guī)則都有優(yōu)先級。它代表觸發(fā)注冊規(guī)則的默認(rèn)順序。默認(rèn)情況下，較低的值表示較高的優(yōu)先級。可以重寫compareTo方法以提供自定義優(yōu)先級策略。

2.2. 定義事實

在Easy Rules中，F(xiàn)act API代表事實

public class Fact<T> { private final String name; private final T value;}

舉個栗子：

Fact<String> fact = new Fact('foo', 'bar');Facts facts = new Facts();facts.add(fact);

或者，也可以用這樣簡寫形式

Facts facts = new Facts();facts.put('foo', 'bar');

用@Fact注解可以將Facts注入到condition和action方法中

@Ruleclass WeatherRule { @Condition public boolean itRains(@Fact('rain') boolean rain) { return rain; } @Action public void takeAnUmbrella(Facts facts) { System.out.println('It rains, take an umbrella!'); // can add/remove/modify facts }}

2.3. 定義規(guī)則引擎

Easy Rules提供兩種RulesEngine接口實現(xiàn)：

DefaultRulesEngine : 根據(jù)規(guī)則的自然順序應(yīng)用規(guī)則 InferenceRulesEngine : 持續(xù)對已知事實應(yīng)用規(guī)則，直到不再適用任何規(guī)則為止

創(chuàng)建規(guī)則引擎：

RulesEngine rulesEngine = new DefaultRulesEngine();// orRulesEngine rulesEngine = new InferenceRulesEngine();

然后，注冊規(guī)則

rulesEngine.fire(rules, facts);

規(guī)則引擎有一些可配置的參數(shù)，如下圖所示：

舉個栗子：

RulesEngineParameters parameters = new RulesEngineParameters() .rulePriorityThreshold(10) .skipOnFirstAppliedRule(true) .skipOnFirstFailedRule(true) .skipOnFirstNonTriggeredRule(true);RulesEngine rulesEngine = new DefaultRulesEngine(parameters);

2.4. 定義規(guī)則監(jiān)聽器

通過實現(xiàn)RuleListener接口

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) { }}

3. 示例

<project xmlns='http://maven.apache.org/POM/4.0.0' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xsi:schemaLocation='http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd'> <modelVersion>4.0.0</modelVersion> <groupId>com.cjs.example</groupId> <artifactId>easy-rules-quickstart</artifactId> <version>1.0.0-SNAPSHOT</version> <packaging>jar</packaging> <dependencies> <dependency> <groupId>org.jeasy</groupId> <artifactId>easy-rules-core</artifactId> <version>4.0.0</version> </dependency> <dependency> <groupId>org.jeasy</groupId> <artifactId>easy-rules-support</artifactId> <version>4.0.0</version> </dependency> <dependency> <groupId>org.jeasy</groupId> <artifactId>easy-rules-mvel</artifactId> <version>4.0.0</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-simple</artifactId> <version>1.7.30</version> </dependency> </dependencies></project>

4. 擴展

規(guī)則本質(zhì)上是一個函數(shù)，如y=f(x1,x2,..,xn)

規(guī)則引擎就是為了解決業(yè)務(wù)代碼和業(yè)務(wù)規(guī)則分離的引擎，是一種嵌入在應(yīng)用程序中的組件，實現(xiàn)了將業(yè)務(wù)決策從應(yīng)用程序代碼中分離。

還有一種常見的方式是Java+Groovy來實現(xiàn)，Java內(nèi)嵌Groovy腳本引擎進行業(yè)務(wù)規(guī)則剝離。

https://github.com/j-easy/easy-rules/wiki

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