Drools簡單專案


在本章中,我們將建立一個Drools專案下列問題說明:

根據不同的城市和各類產品(城和產品的組合),找出當地稅務相關的城市。

我們將有兩個DRL檔案為我們的Drools專案。這兩個檔案的DRL將意味著兩個城市在考慮(Pune和Nagpur)和四類產品(雜貨,藥品,手錶和奢侈品)。

  • 在這兩個城市的藥品稅被認為是零。
  • 雜貨,我們假設了2盧比在Pune和1盧比在Nagpur的一種稅。

我們已經使用了相同的售價以證明不同的輸出。請注意,所有的規則都被觸發了應用。

這裡是模型用來儲存每個專案型別:

package com.sample;

import java.math.BigDecimal;

public class ItemCity {
   public enum City {
      PUNE, NAGPUR
   }
   
   public enum Type {
      GROCERIES, MEDICINES, WATCHES, LUXURYGOODS
   }
   
   private City purchaseCity;
   private BigDecimal sellPrice;
   private Type typeofItem;
   private BigDecimal localTax;
   
   public City getPurchaseCity() {
      return purchaseCity;
   }
   
   public void setPurchaseCity(City purchaseCity) {
      this.purchaseCity = purchaseCity;
   }
   
   public BigDecimal getSellPrice() {
      return sellPrice;
   }
   
   public void setSellPrice(BigDecimal sellPrice) {
      this.sellPrice = sellPrice;
   }
   
   public Type getTypeofItem() {
      return typeofItem;
   }
   
   public void setTypeofItem(Type typeofItem) {
      this.typeofItem = typeofItem;
   }
   
   public BigDecimal getLocalTax() {
      return localTax;
   }
   
   public void setLocalTax(BigDecimal localTax) {
      this.localTax = localTax;
   }
}

DRL檔案

正如前面所說,我們已經用了兩個DRL檔案在這裡:Pune.drl 和Nagpur.drl.

Pune.drl

這是對Pune執行規則的DRL檔案。

// created on: Dec 24, 2014
package droolsexample

// list any import classes here.
import com.sample.ItemCity;
import java.math.BigDecimal;

// declare any global variables here
dialect "java"
rule "Pune Medicine Item"
   
   when
      item : ItemCity (purchaseCity == ItemCity.City.PUNE,
                       typeofItem == ItemCity.Type.MEDICINES)
   
   then
      BigDecimal tax = new BigDecimal(0.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
end

rule "Pune Groceries Item"
   
   when
      item : ItemCity(purchaseCity == ItemCity.City.PUNE,
                      typeofItem == ItemCity.Type.GROCERIES)
   
   then
      BigDecimal tax = new BigDecimal(2.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
end

Nagpur.drl

這是對Nagpur市執行規則的DRL檔案。

// created on: Dec 26, 2014
package droolsexample

// list any import classes here.
import com.sample.ItemCity;
import java.math.BigDecimal;

// declare any global variables here
dialect "java"
rule "Nagpur Medicine Item"
   
   when
      item : ItemCity(purchaseCity == ItemCity.City.NAGPUR, 
                      typeofItem == ItemCity.Type.MEDICINES)

   then
      BigDecimal tax = new BigDecimal(0.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
end

rule "Nagpur Groceries Item"
   
   when
      item : ItemCity(purchaseCity == ItemCity.City.NAGPUR, 
                      typeofItem == ItemCity.Type.GROCERIES)

   then
      BigDecimal tax = new BigDecimal(1.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
end

我們已經寫了基於城市的DRL檔案,因為它為我們提供了可延伸性,以在以後新增任意數量的規則檔案,如果被新增了新的城市。

為了證明所有的規則都可以從我們的規則檔案觸發,我們已經使用了兩種型別的產品(藥物和雜貨); 藥是免稅和雜貨徵稅按城市。

我們的測試類載入規則檔案,插入事實到對談,並產生輸出。

Droolstest.java

package com.sample;

import java.math.BigDecimal;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;

import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderError;
import org.drools.builder.KnowledgeBuilderErrors;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;

import org.drools.io.ResourceFactory;
import org.drools.runtime.StatefulKnowledgeSession;

import com.sample.ItemCity.City;
import com.sample.ItemCity.Type;

/* This is a sample class to launch a rule. */

public class DroolsTest {
   public static final void main(String[] args) {
      try {
      
         // load up the knowledge base
         KnowledgeBase kbase = readKnowledgeBase();
         StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
         
         ItemCity item1 = new ItemCity();
         item1.setPurchaseCity(City.PUNE);
         item1.setTypeofItem(Type.MEDICINES);
         item1.setSellPrice(new BigDecimal(10));
         ksession.insert(item1);
         
         ItemCity item2 = new ItemCity();
         item2.setPurchaseCity(City.PUNE);
         item2.setTypeofItem(Type.GROCERIES);
         item2.setSellPrice(new BigDecimal(10));
         ksession.insert(item2);
         
         ItemCity item3 = new ItemCity();
         item3.setPurchaseCity(City.NAGPUR);
         item3.setTypeofItem(Type.MEDICINES);
         item3.setSellPrice(new BigDecimal(10));
         ksession.insert(item3);
         
         ItemCity item4 = new ItemCity();
         item4.setPurchaseCity(City.NAGPUR);
         item4.setTypeofItem(Type.GROCERIES);
         item4.setSellPrice(new BigDecimal(10));         
         ksession.insert(item4);
         
         ksession.fireAllRules();
         
         System.out.println(item1.getPurchaseCity().toString() + " " 
            + item1.getLocalTax().intValue());
         
         System.out.println(item2.getPurchaseCity().toString() + " "
            + item2.getLocalTax().intValue());
         
         System.out.println(item3.getPurchaseCity().toString() + " "
            + item3.getLocalTax().intValue());
         
         System.out.println(item4.getPurchaseCity().toString() + " "
            + item4.getLocalTax().intValue());
                            
      } catch (Throwable t) {
         t.printStackTrace();
      }
   }
   
   private static KnowledgeBase readKnowledgeBase() throws Exception {
   
      KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
      
      kbuilder.add(ResourceFactory.newClassPathResource("Pune.drl"), ResourceType.DRL);
      kbuilder.add(ResourceFactory.newClassPathResource("Nagpur.drl"), ResourceType.DRL);
      
      KnowledgeBuilderErrors errors = kbuilder.getErrors();
      
      if (errors.size() > 0) {
         for (KnowledgeBuilderError error: errors) {
            System.err.println(error);
         }
         throw new IllegalArgumentException("Could not parse knowledge.");
      }
      
      KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
      kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
      
      return kbase;
   }
}

如果你執行這個程式,它的輸出將如下所示:

PUNE 0
PUNE 20
NAGPUR 0
NAGPUR 10

對於這兩種Pune的和Nagpur,當時該專案是一個醫藥,當地稅務為零;而當該專案是一個雜貨店的產品,該稅是按城市的。更多的規則可以在DRL檔案的其他產品中新增。這僅僅是一個範例程式。

呼叫外部函式形成DRL檔案

在這裡,我們將演示如何從DRL檔案的Java檔案呼叫靜態函式。

首先,建立一個類HelloCity.java在同一個包com.sample中。

package com.sample;

public class HelloCity {
   public static void writeHello(String name) {
      System.out.println("HELLO " + name + "!!!!!!");
   }
}

此後,新增import語句在DRL檔案來呼叫從DRL檔案writeHello方法。在下面的程式碼塊中,修改DRL檔案Pune.drl以黃色突出顯示。

// created on: Dec 24, 2014
package droolsexample

// list any import classes here.
import com.sample.ItemCity;
import java.math.BigDecimal;
 
import com.sample.HelloCity;

//declare any global variables here
dialect "java"

rule "Pune Medicine Item"

   when
      item : ItemCity(purchaseCity == ItemCity.City.PUNE, typeofItem == ItemCity.Type.MEDICINES)

   then
      BigDecimal tax = new BigDecimal(0.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
      HelloCity.writeHello(item.getPurchaseCity().toString());
end

rule "Pune Groceries Item"

   when
      item : ItemCity(purchaseCity == ItemCity.City.PUNE, typeofItem == ItemCity.Type.GROCERIES)
   
   then
      BigDecimal tax = new BigDecimal(2.0);
      item.setLocalTax(tax.multiply(item.getSellPrice()));
end

再次執行程式,其輸出將如下所示:

HELLO PUNE!!!!!!
PUNE 0
PUNE 20
NAGPUR 0
NAGPUR 10

現在,在輸出的差被標記為黃色,顯示在Java類的靜態方法的輸出。

其優點呼叫Java方法是,我們可以用Java編寫的任何效用/輔助函式,並從DRL檔案呼叫相同。