Drools学习笔记2

最新推荐文章于 2021-10-14 18:10:03 发布

转载最新推荐文章于 2021-10-14 18:10:03 发布 · 771 阅读

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#getter #insert #float #exception #session #class

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本文深入解析了Drools API中关键类的作用，包括KnowledgeBuilder、KnowledgeBase、StatefulKnowledgeSession和StatelessKnowledgeSession，并详细介绍了如何通过Drools API执行规则。同时，提供了对Drools的全面理解，包括如何构建规则库、规则执行流程以及不同session对象的特点。

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接上面的代码：

Java代码

public class DroolsTest {
public static final void main(String[] args) {
try {
// load up the knowledge base
KnowledgeBase kbase = readKnowledgeBase();
StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newFileLogger(ksession, "test");
// go !
PeopleEvent pe = new PeopleEvent();
pe.setComming(true);
pe.setRoomId(1);
TemperatureEvent te = new TemperatureEvent();
te.setTemperature(19.5f);
te.setRoomId(1);
ksession.insert(pe);
ksession.insert(te);
ksession.fireAllRules();
logger.close();
} catch (Throwable t) {
t.printStackTrace();
}
}
private static KnowledgeBase readKnowledgeBase() throws Exception {
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add(ResourceFactory.newClassPathResource("FirstRule.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;
}
public static class PeopleEvent {
private boolean isComming;
private int roomId;
public boolean getIsComing() {
return isComming;
}
public void setComming(boolean isComming) {
this.isComming = isComming;
}
public int getRoomId() {
return roomId;
}
public void setRoomId(int roomId) {
this.roomId = roomId;
}
}
public static class TemperatureEvent{
private float temperature;
private int roomId;
public float getTemperature() {
return temperature;
}
public void setTemperature(float temperature) {
this.temperature = temperature;
}
public int getRoomId() {
return roomId;
}
public void setRoomId(int roomId) {
this.roomId = roomId;
}
}
}

public class DroolsTest {    public static final void main(String[] args) {        try {            // load up the knowledge base            KnowledgeBase kbase = readKnowledgeBase();            StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();            KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newFileLogger(ksession, "test");            // go !            PeopleEvent pe = new PeopleEvent();            pe.setComming(true);            pe.setRoomId(1);            TemperatureEvent te =  new TemperatureEvent();            te.setTemperature(19.5f);            te.setRoomId(1);            ksession.insert(pe);            ksession.insert(te);            ksession.fireAllRules();            logger.close();        } catch (Throwable t) {            t.printStackTrace();        }    }    private static KnowledgeBase readKnowledgeBase() throws Exception {        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();        kbuilder.add(ResourceFactory.newClassPathResource("FirstRule.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;    }    public static class PeopleEvent {    	private boolean isComming;    	private int roomId;    			public boolean getIsComing() {			return isComming;		}		public void setComming(boolean isComming) {			this.isComming = isComming;		}		public int getRoomId() {			return roomId;		}		public void setRoomId(int roomId) {			this.roomId = roomId;		}    }    public static class TemperatureEvent{    	private float temperature;    	private int roomId;		public float getTemperature() {			return temperature;		}		public void setTemperature(float temperature) {			this.temperature = temperature;		}		public int getRoomId() {			return roomId;		}		public void setRoomId(int roomId) {			this.roomId = roomId;		}    }}

好了，接下来介绍一下如何来执行Drools是如何来执行规则的，要理解上面的代码首先要清楚Drools API中关于一下几个类的描述：

1) KnowledgeBuilder

KnowledgeBuilder就是用来在业务代码中收集已经编好的规则，找到这些规则并把这些规则文件进行编译，最终产生一批编译好的规则包(KnowledgePackage)给其它的应用程序使用。而创建KnowledgeBuilder对象使用的是KnowledgeBuilderFactory的newKnowledgeBuilder方法。

2) KnowledgeBase

KnowledgeBase 是Drools提供的用来收集应用当中知识（Knowledge）定义的知识库对象，在一个KnowledgeBase 当中可以包含普通的规则、规则流、函数定义、用户自定义对象等。KnowledgeBase本身不包含任何业务数据对象(fact 对象)，业务对象都是插入到由KnowledgeBase产生的两种类型的session对象(StatefulKnowledgeSession和StatelessKnowledgeSession在后面进行介绍)中,而这两种session对象可以用来触发规则。

3) StatefulKnowledgeSession

StatefulKnowledgeSession对象是一种最常用的与规则引擎进行交互的方式，它可以与规则引擎建立一个持续的交互通道。StatefulKnowledgeSession执行完之后一定要调用dispose()方法释放资源。

StatefulKnowledgeSession可以接受外部插入(insert方法)的业务数据——也叫fact，一个对象通常可以对应一个普通的POJO, 而一个POJO有若干个属性来描述这个业务对象，比如一个PeopleEvent中包含了isComing(人是否进来属性), roomed(房间号)，每一个属性对应getter和setter方法，供规则定义来使用（注意：在规则定义中isComing默认的getter方法是getIsComing()）。如果规则当中需要有数据传出，那么可以通过在StatefulKnowledgeSession当中设置global对象来实现，一个global对象也是一个普通的Java对象，在向StatefulKnowledgeSession当中设置global对象时不用insert方法而用setGlobal方法实现。

4) StatelessKnowledgeSession

StatelessKnowledgeSession是在StatefulKnowledgeSession基础上进行进一步的封装，它跟StatefulKnowledgeSession的区别就是它不在需要调用dispose()方法释放内存资源了，但它不能重复的插入fact的操作、也不能重复的调用fireAllRules()方法来执行所有的规则，因为它不能保存状态，对应的这些要完成的工作在StatelessKnowledgeSession当中只有execute()方法，通过这个方法可以实现插入所有的fact并且可以同时执行所有的规则或规则流。

结合上面的代码应该可以更好的了解这四个概念。下面介绍如何更好的使用Drools。