drools初接触

Drool是jboss的规则引擎, 老早就想看看了, 前断时间忙的一直没有时间.现在抽空学习一下.记录一下学习的心得体会, 也算给今年一个交代.

是
一. 环境配置.
最快的方法:
下载Drool的eclipse插件:
http://www.jboss.org/drools/downloads.html

此插件功能不错, 写rule很方便, 并且能创建 drool project, 所有依赖
的jar包都有包含,

二: hello world
晦涩的理论先放一边, 跑一个hello world再说:

1. packagecom.sample;
3. importjava.io.InputStreamReader;
4. importjava.io.Reader;
6. importorg.drools.RuleBase;
7. importorg.drools.RuleBaseFactory;
8. importorg.drools.WorkingMemory;
9. importorg.drools.compiler.PackageBuilder;
10. importorg.drools.rule.Package;
12. /**
13. *Thisisasamplefiletolauncharulepackagefromarulesourcefile.
14. */
15. publicclassDroolsTest{
17. publicstaticfinalvoidmain(String[]args){
18. try{
20. //loaduptherulebase
21. RuleBaseruleBase=readRule();
22. WorkingMemoryworkingMemory=ruleBase.newStatefulSession();
24. //go!
25. Messagemessage=newMessage();
26. message.setMessage("HelloWorld");
27. message.setStatus(Message.HELLO);
28. workingMemory.insert(message);
29. workingMemory.fireAllRules();
32. }catch(Throwablet){
33. t.printStackTrace();
34. }
35. }
37. /**
38. *Pleasenotethatthisisthe"lowlevel"ruleassemblyAPI.
39. */
40. privatestaticRuleBasereadRule()throwsException{
41. //readinthesource
42. Readersource=newInputStreamReader(DroolsTest.class.getResourceAsStream("/Sample.drl"));
44. //optionallyreadintheDSL(ifyouareusingit).
45. //Readerdsl=newInputStreamReader(DroolsTest.class.getResourceAsStream("/mylang.dsl"));
47. //Usepackagebuildertobuilduparulepackage.
48. //Analternativelowerlevelclasscalled"DrlParser"canalsobeused...
50. PackageBuilderbuilder=newPackageBuilder();
52. //thiswilparseandcompileinonestep
53. //NOTE:Thereare2methodshere,theoneargumentoneisfornormalDRL.
54. builder.addPackageFromDrl(source);
56. //UsethefollowinginsteadofaboveifyouareusingaDSL:
57. //builder.addPackageFromDrl(source,dsl);
59. //getthecompiledpackage(whichisserializable)
60. Packagepkg=builder.getPackage();
62. //addthepackagetoarulebase(deploytherulepackage).
63. RuleBaseruleBase=RuleBaseFactory.newRuleBase();
64. ruleBase.addPackage(pkg);
65. returnruleBase;
66. }
68. publicstaticclassMessage{
69. publicstaticfinalintHELLO=0;
70. publicstaticfinalintGOODBYE=1;
71. publicstaticfinalintGAME_OVER=2;
73. privateStringmessage;
75. privateintstatus;
77. publicStringgetMessage(){
78. returnthis.message;
79. }
81. publicvoidsetMessage(Stringmessage){
82. this.message=message;
83. }
85. publicintgetStatus(){
86. returnthis.status;
87. }
89. publicvoidsetStatus(intstatus){
90. this.status=status;
91. }
92. }
94. }

rule文件:
Sample.drl

1. packagecom.sample
3. importcom.sample.DroolsTest.Message;
5. rule"HelloWorld"
6. when
7. m:Message(status==Message.HELLO,message:message)
8. then
9. System.out.println(message);
10. m.setMessage("Goodbyecruelworld");
11. m.setStatus(Message.GOODBYE);
12. update(m);
13. end
15. rule"GoodBye"
16. no-looptrue
17. when
18. m:Message(status==Message.GOODBYE,message:message)
19. then
20. System.out.println(message);
21. m.setStatus(Message.GAME_OVER);
22. m.setMessage("gameovernow!");
23. update(m);
24. end
26. rule"gameover"
27. when
28. m:Message(status==Message.GAME_OVER)
29. then
30. System.out.println(m.getMessage());
31. end
33. java代码就不说了,简单解释一下rule文件:
35. rule"HelloWorld"
36. when
37. m:Message(status==Message.HELLO,message:message)
38. then
39. System.out.println(message);
40. m.setMessage("Goodbyecruelworld");
41. m.setStatus(Message.GOODBYE);
42. update(m);
43. end

java代码就不说了, 主要说明一下rule文件, 熟悉一下rule语法:
1:规则的主体结构:
rule "name"
ATTRIBUTES
when
LHS
then
RHS
end

其中:
LHS(left hand side)是规则的条件部分, RHS(right hand side)是条件满足后的自行块.

2: 条件的书写:
m : Message( status == Message.HELLO, message : message )
意思是:
在working Memory中, 如果有一个Message的instance满足如下条件:
它的status熟悉等于Message.HELLO.
满足条件的Message instance 用变量 m表示, 它的message属性用message变量表示, 以便在RHS中使用.

3: 条件满足后的自行块(RHS)

System.out.println( message );
m.setMessage( "Goodbye cruel world" );
m.setStatus( Message.GOODBYE );
update( m );
用到了在LHS中 定义的变量: m, message
update( m )表示把此Message instance在 working memory中更新.这便会触发名称为"GoodBye"的rule, 进而触发名称为"game over"的rule.

以下是drools提供的demo, 稍微整理了下, 可直接在eclipse中import进来

http://lcllcl987.iteye.com/blog/255404
(前提: 下载并安装Drool的eclipse插件:Drools 4.0.7 Eclipse Workbench for 3.2 )
建议首先看看:
FibonacciExample: Fibonacci数列的drools实现.
GolfingExample: 著名的golf智力问题的drools实现,golf.drl的注释就是此问题的文字描述.
ShoppingExample: 一个shopping打折的demo, 超过100元, 有10元的折扣.
StateExampleUsingAgendGroup: By setting dynamic to TRUE, Drools will use JavaBean, PropertyChangeListeners so you don't have to call update().
StateExampleWithDynamicRules: 动态加载rule的一个demo(加载StateExampleUsingSalience.drl后在加载StateExampleDynamicRule.drl).

TroubleTicketExample:
使用了duration规则特性: 将指定的规则延迟一定时间运行
规则引擎是在另外一个线程中进行的，因此使用了duration特性可以将指定的规则延迟一定时间运行.
但是要注意的是主线程中也需要做相应的延时，否则主线程结束后不会再处理子线程的结果
salience 和 duration特性影响rule的执行顺序.
其次demo还定义了一个rule function.