Simple use of Rule Engine drools

The rule engine is applicable to complex and variable rules, such as product full reduction, bonus points, and attendance rules.

1. Introduce Maven dependency

<dependency>    <groupId>org.drools</groupId>    <artifactId>drools-core</artifactId>    <version>7.13.0.Final</version></dependency><dependency>    <groupId>org.drools</groupId>    <artifactId>drools-compiler</artifactId>    <version>7.13.0.Final</version></dependency>

　　

2. drools can be executed in two ways. The first is based on the kmodule. xml and DRL configuration files, and the second is the dynamic read Rule.

Kmodule-based

1) create a fact. The fact in drools is a common bean in Java and is used to pass parameters.

package com.beyond.odc.entity;/** * Fact java bean * @author Hejinsheng */public class Message {    private String message;    private String result;    private int status;    public String getMessage() {        return this.message;    }    public void setMessage(String message) {        this.message = message;    }    public int getStatus() {        return this.status;    }    public void setStatus(int status) {        this.status = status;    }    public String getResult() {        return result;    }    public void setResult(String result) {        this.result = result;    }}

　　

2) Create the kmodule. xml file under resources/META-INF with the following content:

<?xml version="1.0" encoding="UTF-8"?><kmodule xmlns="http://jboss.org/kie/6.0.0/kmodule">    <kbase name="rules" packages="rules">        <ksession name="ksession-rules"/>    </kbase></kmodule>

　　

3) Create the rule description file rules. DRL in the resources/rules folder. The content is as follows:

Package rulesimport COM. beyond. ODC. entity. message; rule "hello" no-loop true lock-on-active true when $ message: Message (status = 0) Then system. out. println ("message:" + $ message. getmessage (); $ message. setresult ("Hello Response Message"); Update ($ message) endrule "Byebye" no-loop true lock-on-active true when $ message: Message (status = 1) then system. out. println ("message:" + $ message. getmessage (); $ message. setresult ("Byebye Response Message"); Update ($ message) End

　　

4) Compile the test file

Public static void main (string [] ARGs) {try {kiesession ksession = kiecontainerfactory. getkiecontainer (). newkiesession ("ksession-Rules"); message = new message (); message. setmessage ("hello"); // corresponds to the rule name in the DRL file, indicating the rule message to be executed. setstatus (0); // obtain a field in the message, and determine whether to execute the code block ksession in the user rule file. insert (Message); // pass the message as the passed parameter to drools to execute ksession. fireallrules (); // load the rule system. out. println ("received messages from drools:" + message. getresult (); // If response parameters exist in drools, you can use the field to get} catch (throwable t) {T. printstacktrace ();}}

　　

// Kiecontainerfactory code snippet public class kiecontainerfactory {Private Static kiecontainer; public static kiecontainer getkiecontainer () {If (kiecontainer = NULL) {// load up the knowledge base kieservices Ks = kieservices. factory. get (); kiecontainer kcontainer = Ks. getkieclasspathcontainer (); kiecontainer = kcontainer;} return kiecontainer ;}}

　　

5) The execution result indicates that the code has been executed to the drools file. The specific business logic can be implemented in the code block after then.

Incoming, message: Hello received from drools: Hello Response Message

　　

Iii. Dynamic execution

Generally, it refers to the description of a rule obtained from a database or remotely for rule execution. In the dynamic mode, kmodule. xml and DRL files are not required, making execution easier.

Public static void execfromdb () {kiesession ksession = NULL; try {// check the rules from the database according to the code according to the actual situation, here, the string rule = "package rules \ n" + "\ n" + "Import COM. beyond. ODC. entity. message; \ n "+" \ n "+" rule \ "Hello \" \ n "+" no-loop true \ n "+" lock-on-active true \ n "+ "When \ n" + "$ message: message (status = 0) \ n "+" then \ n "+" system. out. println (\ "dynamic execution, message: \" + $ message. getmessage (); \ n "+" $ message. setresult (\ "H Hello, the Response Message \ "); \ n" + "Update ($ message) \ n "+" End \ n "+" \ n "+" rule \ "Byebye \" \ n "+" no-loop true \ n "+" lock-on- active true \ n "+" When \ n "+" $ message: message (status = 1) \ n "+" then \ n "+" system. out. println (\ "dynamic execution, message: \" + $ message. getmessage (); \ n "+" $ message. setresult (\ "Byebye Response Message \"); \ n "+" Update ($ message) \ n "+" end "; knowledgebuilder kb = knowledgebuilderfactory. newknowledgebuilder (); kb. Add (resourcefactory. newbytearrayresource (rule. getbytes ("UTF-8"), resourcetype. DRL); // check rule correctness knowledgebuildererrors errors = kb. geterrors (); For (knowledgebuildererror error: errors) {system. out. println ("rule file correctness error: {}" + error);} internalknowledgebase kbase = knowledgebasefactory. newknowledgebase (); kbase. addpackages (kb. getknowledgepackages (); // executes the rule ksession = kbase. newkiesession (); // fac T message fact = new message (); fact. setmessage ("Byebye"); fact. setstatus (1); ksession. insert (fact); ksession. fireallrules (); system. out. println ("messages received from drools rules:" + fact. getresult ();} catch (exception e) {system. out. println ("rule execution exception: {}" + E) ;}finally {If (null! = Ksession) ksession. Dispose ();}}

The execution result is as follows:

Message: the message received by Byebye from the drools rule: the message returned by Byebye.

　　

 

Simple use of Rule Engine drools