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规则引擎:Drools与JRuleEngine


规则引擎:Drools与JRuleEngine

译文:《规则引擎:Drools与JRuleEngine》
译者:chszs
作者:Vivek Tomar
原文:《Rule engine : Drools / JRuleEngine》
原文见http://www.naxos-software.de/blog/index.php?/archives/78-Rule-engine-Drools-JRuleEngine.html

一、规则引擎
规则引擎有助于基于存储在规则中的知识和推理来执行判断。这些规则基本上只有条件和动作,别无它物。

规则引擎的优点:
1、分隔应用程序的条件和控制流
(1) 规则都存储在单独的文件。
(2) 规则可以被技术人士和商业人士修改的。
(3) 规则改变后应用程序不必重新部署。
(4) 使用集中的规则使得应用程序更易于管理和维护。
 
2、规则替换了代码中的if else语句
(1) 规则脚本更容易提取。
(2) 即使是非技术人员也能轻易地遵循规则。
(3) 集中可以解决问题,而不是实现。
(4) 与实现代码相比,规则聚团更容易编写。 

3、为什么作决定能很容易地概念化

总结:规则有助于消除代码中大量的if else语句,使代码更易于维护。

二、Drools介绍
Drools是一个开源实现。它是一个Java库,以Apache许可证发布,其二进制代码或源码下载均有效。

推理机的核心是一个规则引擎。它执行模式匹配,在执行动作中做出决策。RETE算法用于模式匹配。 

知识被表述为规则。规则有两个主要部分:条件和动作。

例如:
如果用户(年龄>17),那么System.out.println("User is greater then 17");

在人工智能系统,主要有两种响应的方法。
1、正向链(Forward Chaining)
这是基于事实根据的。在工作区域检查中规则。当规则条件为真的规则不再有时,模式匹配结束。

2、反向链(Backward Chaining)
只检查规则的动作可以匹配目标的规则。如果满足条件,然后进行评估。

3、兼容JDK1.4,且需要下面的库。
(1) drools-all-jdk1.4.2.1.jar
(2) xercesImpl-2.6.2.jar
(3) antlr-2.7.5.jar
(4) janino-2.3.2.jar

4、代码示例(ApplyRule.java)

/*
  /* $Header$
  */

  package com.vivek.drools.example;

  import java.io.IOException;
  import java.io.InputStream;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.drools.FactException;
  import org.drools.IntegrationException;
  import org.drools.RuleBase;
  import org.drools.WorkingMemory;
  import org.drools.io.RuleBaseLoader;
  import org.xml.sax.SAXException;

  /**
  * Demonstration of a sample rule using Java.
  *
  * @version <tt>$Revision: 1.0 $</tt>
  * @author <a href="mailto:{vivek.tomar@naxos-software.de}" mce_href="mailto:{vivek.tomar@naxos-software.de}">{Vivek Tomar}</a>.
  */

  public class ApplyRule {

  // Constants -----------------------------------------------------

  static Log log = LogFactory.getLog(ApplyRule.class.getName());
  private static final String RULE_FILE = "/rules/rules.drl";
  //private static final String RULE_IS_TURNOVER_INSURABLE = "turnoverInsurable";
  //private static final String RULE_IS_TURNOVER_NOT_INSURABLE = "turnoverNotInsurable";

  // Attributes ----------------------------------------------------

  private double turnover = 1000000;

  // Constructors --------------------------------------------------

  public ApplyRule () {
  try {
  InputStream in = this.getClass().getResourceAsStream(RULE_FILE);
  RuleBase ruleBase = RuleBaseLoader.loadFromInputStream(in);
  WorkingMemory workingMemory = ruleBase.newWorkingMemory();
  workingMemory.assertObject(this);
  // Fire specific rule
  //workingMemory.fireAllRules(new RuleNameEqualsAgendaFilter(RULE_IS_TURNOVER_INSURABLE));

  //Fire all rules
  workingMemory.fireAllRules();
  } catch (IntegrationException e) {
  e.printStackTrace();
  } catch (FactException e) {
  e.printStackTrace();
  } catch (SAXException e) {
  e.printStackTrace();
  } catch (IOException e) {
  e.printStackTrace();
  }
  }

  // Public --------------------------------------------------------

  public static void main (String args[]) {
  new ApplyRule();
  }

  public double getTurnover () {
  return turnover;
  }

  public void setTurnover (double turnover) {
  this.turnover = turnover;
  }

  public void printCompanyInsurable () {
  log.info("******************************");
  log.info("This company is Insurable.");
  log.info("******************************");
  }

  public void printCompanyNotInsurable () {
  log.info("==============================");
  log.info("This company is not Insurable.");
  log.info("==============================");
  }
  }



规则定义(rules.drl)

<?xml version="1.0"?>
<rule-set name="cheese rules"
  xmlns="http://drools.org/rules"
  xmlns:java="http://drools.org/semantics/java"
  xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
  xs:schemaLocation="http://drools.org/rules rules.xsd
  http://drools.org/semantics/java java.xsd">
<rule name="turnoverInsurable">
<parameter identifier="applyRule">
<class>com.vivek.drools.example.ApplyRule</class>
</parameter>
<java:condition>applyRule.getTurnover() > 2000000 </java:condition>
<java:consequence>
  applyRule.printCompanyInsurable();
</java:consequence>
</rule>
<rule name="turnoverNotInsurable">
<parameter identifier="applyRule">
<class>com.vivek.drools.example.ApplyRule</class>
</parameter>
<java:condition>applyRule.getTurnover() < 2000000 </java:condition>
<java:consequence>
  applyRule.printCompanyNotInsurable();
</java:consequence>
</rule>
</rule-set>



三、JRuleEngine介绍
JRuleEngine是一个基于Java的规则引擎,遵循JSR94规范,版本1.1。

1、JRuleEngine共同特征: 
(1) 在JRuleEngine输入对象被称为事实,而输出对象被称为结论。 
(2) 一个类的方法可直接从规则中调用。 

2、JRuleEngine基于前向链算法。

3、规则是类org.jruleengine.rule.RuleImpl的对象,它们以下列方式载入:
(1) 可以从XML文件中读入
(2) 通过RuleImpl对象创建,也可以取自数据库。

4、会话是客户端和规则引擎之间的运行时的胶水。会话与单一的规则执行集相关。会话规则的类型:
(1) 一个有状态的规则会话可持续很长时间,可一次又一次地查询。
(2) 一个无状态的规则给出了实现,但只能持续一定时期。

5、JRuleEngine需要两个库:
(1) jsr94.jar
(2) jruleengine.jar

6、添加这些文件到您应用程序的类路径。

7、通过实例化一个有状态的规则会话(StatefulRuleSession)或无状态的规则会话(StatelessRuleSession)来使用这个库。

8、代码例子(ApplyRule.java)

/*
  * $Header$
  */
  package com.vivek.jruleengine.example;

  import java.io.InputStream;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;

  import javax.rules.RuleRuntime;
  import javax.rules.RuleServiceProvider;
  import javax.rules.RuleServiceProviderManager;
  import javax.rules.StatelessRuleSession;
  import javax.rules.admin.RuleAdministrator;
  import javax.rules.admin.RuleExecutionSet;

  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;

  /**
  * Demonstration of a sample rule using Java.
  *
  * @version <tt>$Revision: 1.0 $</tt>
  * @author <a href="mailto:{vivek.tomar@naxos-software.de}" mce_href="mailto:{vivek.tomar@naxos-software.de}">{Vivek Tomar}</a>.
  */
  public class ApplyRule {

  // Constants -----------------------------------------------------

  static Log log = LogFactory.getLog(ApplyRule.class.getName());
  private static final String RULE_FILE = "/rules/rules.xml";

  // Attributes ----------------------------------------------------

  private double turnover = 1000000;

  // Constructors --------------------------------------------------

  public ApplyRule () {

  try {
  // Load the rule service provider of the reference
  // implementation.
  // Loading this class will automatically register this
  // provider with the provider manager.
  Class.forName("org.jruleengine.RuleServiceProviderImpl");

  // Get the rule service provider from the provider manager.
  RuleServiceProvider serviceProvider = RuleServiceProviderManager.getRuleServiceProvider("org.jruleengine");

  // get the RuleAdministrator
  RuleAdministrator ruleAdministrator = serviceProvider.getRuleAdministrator();
  log.info("Administration API");
  log.info("======================");
  log.info("Acquired RuleAdministrator: ");

  // get an input stream to a test XML ruleset
  // This rule execution set is part of the TCK.
  InputStream inStream = this.getClass().getResourceAsStream(RULE_FILE);
   

  // parse the ruleset from the XML document
  RuleExecutionSet res1 =
  ruleAdministrator.getLocalRuleExecutionSetProvider(null).createRuleExecutionSet(inStream, null);
  inStream.close();
  log.info("Loaded RuleExecutionSet: ");

  // register the RuleExecutionSet
  String uri = res1.getName();
  ruleAdministrator.registerRuleExecutionSet(uri, res1, null);
  log.info("Bound RuleExecutionSet to URI: " + uri);

  RuleRuntime ruleRuntime = serviceProvider.getRuleRuntime();
  log.info("Acquired RuleRuntime: ");

  // create a StatelessRuleSession
  StatelessRuleSession statelessRuleSession = (StatelessRuleSession)
  ruleRuntime.createRuleSession(uri, new HashMap(),
  RuleRuntime.STATELESS_SESSION_TYPE);

  log.info("Got Stateless Rule Session: " + statelessRuleSession);

  // call executeRules with some input objects

  // Create a input list.
  List input = new ArrayList();
  input.add(this);

  // Print the input.
  log.info("Calling rule session with the following data");
  log.info("Customer turnover input: " + this.getTurnover());

  // Execute the rules without a filter.
  List results = statelessRuleSession.executeRules(input);

  // Release the session.
  statelessRuleSession.release();
  log.info("Released Stateless Rule Session.");

  } catch (NoClassDefFoundError e) {
  if (e.getMessage().indexOf("Exception") != -1) {
  log.error("Error: The Rule Engine Implementation could not be found.");
  } else {
  log.error("Error: " + e.getMessage());
  }
  } catch (Exception e) {
  e.printStackTrace();
  }
  }

  // Public --------------------------------------------------------

  public static void main (String args[]) {
  new ApplyRule();
  }

  public double getTurnover () {
  return turnover;
  }

  public void setTurnover (double turnover) {
  this.turnover = turnover;
  }

  public void printCompanyInsurable () {
  log.info("******************************");
  log.info("This company is Insurable.");
  log.info("******************************");
  }

  public void printCompanyNotInsurable () {
  log.info("==============================");
  log.info("This company is not Insurable.");
  log.info("==============================");
  }
  }

规则定义(rules.xml)

<?xml version="1.0" encoding="UTF-8"?>
<rule-execution-set>
<name>RuleExecutionSet1</name>
<description>Rule Execution Set</description>
<synonymn name="applyRule" class="com.vivek.jruleengine.example.ApplyRule" />
<rule name="turnoverInsurable" description="Check if turnover insurable" >
<if leftTerm="applyRule.getTurnover" op=">" rightTerm="2000000" />
<then method="applyRule.printCompanyInsurable()" />
</rule>
<rule name="turnoverNotInsurable" description="Check if turnover not insurable" >
<if leftTerm="applyRule.getTurnover" op="<" rightTerm="2000000" />
<then method="applyRule.printCompanyNotInsurable" />
</rule>
</rule-execution-set>



结论:
Drools除了提供正常的规则引擎的能力,还有以下额外的优点:
(1) 无论是技术人士还是商业人士,Drools都是用户友好的,它提供了一个巨大的支持工具集。
(2) Drools的Reteoo算法可加速和可扩展。
(3) Drools提供的Eclipse插件带有自动完成智能感知和调试视图、规则流GUI等。
(4) 基于Web的工具(Guvnor):是一个业务规则管理系统(BRMS),它提供了高级规则授权、版本控制和管理。

至于其他的规则引擎,我个人建议在项目中使用Drools,因为它有一个很大的支持社区。在IDE支持和基于Web的规则管理工具(Guvnor)也有很大优势。

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