Java规则引擎Easy Rules的使用介绍

@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!");
  }
}

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();

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!\");");

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"));

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);
  }
}

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

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

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");
  }

}

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.

}

@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
  }
}

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

//Create a composite rule from two primitive rules
UnitRuleGroup myUnitRuleGroup = new UnitRuleGroup("myUnitRuleGroup", "unit of myRule1 and myRule2");
myUnitRuleGroup.addRule(myRule1);
myUnitRuleGroup.addRule(myRule2);

//Register the composite rule as a regular rule
Rules rules = new Rules();
rules.register(myUnitRuleGroup);

RulesEngine rulesEngine = new DefaultRulesEngine();
rulesEngine.fire(rules, someFacts);

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

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

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

@Rule
class 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
  }

}

RulesEngine rulesEngine = new DefaultRulesEngine();

// or

RulesEngine rulesEngine = new InferenceRulesEngine();

rulesEngine.fire(rules, facts);

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

RulesEngine rulesEngine = new DefaultRulesEngine(parameters);

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) { }

}

<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>