📅  最后修改于: 2020-10-15 10:58:25             🧑  作者: Mango
在本章中,我们将为以下问题陈述创建一个Drools项目-
根据城市和产品种类(城市与产品的组合),找出与该城市相关的地方税。
我们的Drools项目将有两个DRL文件。这两个DRL文件将表示正在考虑的两个城市(浦那和那格浦尔)和四种产品(杂货,药品,钟表和奢侈品)。
两个城市的药品税都被视为零。
对于杂货,我们假设在浦那征收2卢比的税,在那格浦尔征收1卢比的税。
我们使用相同的售价来展示不同的输出。请注意,所有规则都在应用程序中触发。
这是保存每个itemType的模型-
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;
}
}
如前所述,我们在这里使用了两个DRL文件:Pune.drl和Nagpur.drl。
这是执行浦那城市规则的DRL文件。
// 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
这是执行那格浦尔市规则的DRL文件。
// 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
我们已经基于城市编写了DRL文件,因为如果要添加新的城市,它可以为以后添加任意数量的规则文件提供扩展性。
为了证明所有规则都是从规则文件中触发的,我们使用了两种项目类型(药品和食品杂货)。药品是免税的,杂货则按城市征税。
我们的测试类加载规则文件,将事实插入会话中,并产生输出。
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;
}
}
如果运行此程序,其输出将如下所示:
PUNE 0
PUNE 20
NAGPUR 0
NAGPUR 10
对于浦那和那格浦尔而言,当该商品为药品时,地方税为零;而当该商品为杂货产品时,则按城市征收税款。可以在其他产品的DRL文件中添加更多规则。这只是一个示例程序。
在这里,我们将演示如何从DRL文件中的Java文件中调用静态函数。
首先,在同一包com.sample中创建一个类HelloCity.java 。
package com.sample;
public class HelloCity {
public static void writeHello(String name) {
System.out.println("HELLO " + name + "!!!!!!");
}
}
此后,在DRL文件中添加import语句以从DRL文件中调用writeHello方法。在下面的代码块中,DRL文件Pune.drl中的更改以黄色突出显示。
// 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
再次运行该程序,其输出如下:
HELLO PUNE!!!!!!
PUNE 0
PUNE 20
NAGPUR 0
NAGPUR 10
现在,输出中的差异以黄色标记,显示了Java类中静态方法的输出。
调用Java方法的好处是我们可以用Java编写任何实用程序/帮助程序函数,并从DRL文件中调用它。