drools

Drools規則引擎初學入門實例HelloWorld

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EclipseJBossUPIDEGo
2009-01-14 11:32（1）下載eclipse（www.eclipse.org），如果是一般的java開發，下載Eclipse IDE for Java Developers就行了，解壓後即可使用；

（2）下載Drools（http://jboss.org/drools/downloads.html），目前最新版本是Drools 4.0.7 Binaries，下載後解壓即可；

（3）之後下載eclipse的Drools插件，版本跟eclipse對應，目前有Drools 4.0.7 Eclipse 3.2 Workbench和Drools 4.0.7 Eclipse Europa 3.3 Workbench兩種。

Drools插件解壓後，將裏面的org.drools.eclipse_4.0.7.jar文件copy到eclipse的plugins目錄中，重啓eclipse，在工具欄可以看到一個 圖標，這就是Drools的工作臺，之後就可通過這個按鈕創建Drools resource文件了。

（4）開始Hello World

Java文件：DroolsTest.java

package com.sample;

import java.io.InputStreamReader;
import java.io.Reader;

import org.drools.RuleBase;
import org.drools.RuleBaseFactory;
import org.drools.WorkingMemory;
import org.drools.compiler.PackageBuilder;
import org.drools.rule.Package;

/**
* This is a sample file to launch a rule package from a rule source file.
*/
public class DroolsTest {

public static final void main(String[] args) {
try {

//load up the rulebase
RuleBase ruleBase = readRule();
WorkingMemory workingMemory = ruleBase.newStatefulSession();

//go !
Message message = new Message();
message.setMessage( "Hello World" );
message.setStatus( Message.HELLO );
workingMemory.insert( message );
workingMemory.fireAllRules();


} catch (Throwable t) {
t.printStackTrace();
}
}

/**
* Please note that this is the "low level" rule assembly API.
*/
private static RuleBase readRule() throws Exception {
//read in the source
Reader source = new InputStreamReader( DroolsTest.class.getResourceAsStream( "/Sample.drl" ) );

//optionally read in the DSL (if you are using it).
//Reader dsl = new InputStreamReader( DroolsTest.class.getResourceAsStream( "/mylang.dsl" ) );

//Use package builder to build up a rule package.
//An alternative lower level class called "DrlParser" can also be used...

PackageBuilder builder = new PackageBuilder();

//this wil parse and compile in one step
//NOTE: There are 2 methods here, the one argument one is for normal DRL.
builder.addPackageFromDrl( source );

//Use the following instead of above if you are using a DSL:
//builder.addPackageFromDrl( source, dsl );

//get the compiled package (which is serializable)
Package pkg = builder.getPackage();

//add the package to a rulebase (deploy the rule package).
RuleBase ruleBase = RuleBaseFactory.newRuleBase();
ruleBase.addPackage( pkg );
return ruleBase;
}

public static class Message {
public static final int HELLO = 0;
public static final int GOODBYE = 1;
public static final int GAME_OVER = 2;

private String message;

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;
}
}

}
選擇插件Drools按鈕裏的"New Rule resource"，建立規則（rule）文件：Sample.drl

package com.sample

import com.sample.DroolsTest.Message;

rule "Hello World"
when
m : Message( status == Message.HELLO, message : message )
then
System.out.println( message );
m.setMessage( "Goodbye cruel world" );
m.setStatus( Message.GOODBYE );
update( m );
end

rule "GoodBye"
no-loop true
when
m : Message( status == Message.GOODBYE, message : message )
then
System.out.println( message );
m.setStatus(Message.GAME_OVER);
m.setMessage("game over now!");
update( m );
end

rule "game over"
when
m : Message( status == Message.GAME_OVER)
then
System.out.println( m.getMessage() );
end
注意：文件要放在相應的包裏，然後編譯—執行，當時出現了錯誤，查找資料，還需要加載包，包括：

<1> Drools 4.0.7目錄下的drools-core-4.0.7.jar，drools-compiler-4.0.7.jar

<2> Drools 4.0.7\lib目錄下的antlr-runtime-3.0.jar，mvel-1.3.1-java1.4.jar

<3>以及eclipse\plugins目錄下的org.eclipse.jdt.core_3.2.3.v_686_R32x.jar（不同版本，包名會稍有不同）。

重新運行，應該就不會有錯了。執行結果如下：

Hello World
Goodbye cruel world
game over now!