[英]How to write Stateful and Time-based rules in Drools?
我正在尝试使用 Drools 编写基于规则的引擎。 规则是这样的:
规则“警报”:如果状态为“警报”,则立即发送通知。
规则“警告”:如果状态为“警告”,则将设备 ID 保存在内存中并等待 5 分钟。 如果在 5 分钟内收到另一条具有相同设备 ID 和状态“已解决”的消息,则取消此规则。 否则,将状态升级为警报并触发规则“警报”。
规则“已解决”:如果状态为“已解决”且设备 ID 已在内存中,则清除该设备 ID 的“警告”,即从内存中删除设备 ID。
规则警报很容易并且正在工作。 但是规则警告和已解决显然在我的代码中不起作用。 如何在 Drools 中编写这样的规则?
这是我到目前为止编写的代码:
package com.sample;
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.logger.KnowledgeRuntimeLogger;
import org.drools.logger.KnowledgeRuntimeLoggerFactory;
import org.drools.runtime.StatefulKnowledgeSession;
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 !
MachineMessage[] messages = new MachineMessage[4];
messages[0] = new MachineMessage("1", "Warning");
messages[1] = new MachineMessage("2", "Alarm");
messages[2] = new MachineMessage("3", "Alarm");
messages[3] = new MachineMessage("1", "Resolved");
for(int i = 0; i < messages.length; i++)
{
ksession.insert(messages[i]);
ksession.fireAllRules();
Thread.sleep(9000);
}
logger.close();
} catch (Throwable t) {
t.printStackTrace();
}
}
private static KnowledgeBase readKnowledgeBase() throws Exception {
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add(ResourceFactory.newClassPathResource("Sample.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 MachineMessage {
private String deviceID;
private String status;
public MachineMessage() { }
public MachineMessage(String deviceID, String status) {
this.deviceID = deviceID;
this.status = status;
}
public String getDeviceID() {
return this.deviceID;
}
public void setDeviceID(String deviceID) {
this.deviceID = deviceID;
}
public String getStatus() {
return this.status;
}
public void setStatus(String status) {
this.status = status;
}
}
}
package com.sample
import com.sample.DroolsTest.MachineMessage;
rule "Alarm"
when
m : MachineMessage( status == "Alarm", myDeviceID : deviceID )
then
System.out.println("Send notification to technician, device in Alarm state. Device ID: " + myDeviceID );
end
rule "Warning"
when
m : MachineMessage( status == "Warning", myDeviceID : deviceID )
then
System.out.println("Wait for 5 minutes, device in Warning state. Device ID: " + myDeviceID);
// if we get Machine Message with the same device ID and Resolved status in 5 minutes then
// we'll not trigger the following line
m.setStatus("Alarm");
update(m);
end
rule "Resolved"
when
m : MachineMessage( status == "Resolved", myDeviceID : deviceID )
then
System.out.println("Device has resolved its warning state. Device ID: " + myDeviceID);
end
我得到的实际输出是这样的:
Wait for 5 minutes, device in Warning state. Device ID: 1
Send notification to technician, device in Alarm state. Device ID: 1
Send notification to technician, device in Alarm state. Device ID: 2
Send notification to technician, device in Alarm state. Device ID: 3
Device has resolved its warning state. Device ID: 1
而我想要:
Wait for 5 minutes, device in Warning state. Device ID: 1
Send notification to technician, device in Alarm state. Device ID: 2
Send notification to technician, device in Alarm state. Device ID: 3
Device has resolved its warning state. Device ID: 1
作为最佳实践,允许应用程序填充未填充的事件属性(以使用推断数据丰富事件),但不应更改已填充的属性。
如此明确的规则“警告”已经按照 OP 提出的方式(改变字段“状态”)未能满足 CEP 的第一个要求。
一个潜在的建议是:
rule "Warning"
when
m : MachineMessage( status == "Warning", myDeviceID : deviceID )
not( MachineMessage( status == "Resolved", deviceID == m.deviceID, this after[0s, 30s] m) )
then
System.out.println("I waited for 5 minutes, device in Warning state not followed by Resolved. Device ID: " + myDeviceID);
insert(new MachineMessage(m.deviceID, "Alarm"));
end
这不会改变现有事件的任何已赋值字段,并且实际上会使 CEP 知识推理尝试匹配 OP 描述的业务需求。
一般而言,Drools 手册中关于喷水灭火/火警的 CEP 示例似乎与 OP 描述的业务需求一致。
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