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2.关于DROOLS规则引擎的图书那里有卖的,急需啊!
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关于DROOLS规则引擎的图书那里有卖的,急需啊!
InfoQ发布了一个关于规则引擎的介绍Real-World Rule Engines,原文 /articles/Rule-Engines
ONJava上也有两篇文章:
Give Your Business Logic a Framework with Drools /lpt/a/
Using Drools in Your Enterprise Java Application /lpt/a/
下面总结一下其中的精华:
大多数web和企业Java应用可以分成三个部分:一个和用户交互的前台, 一个和后台系统,例如数据库交互的服务层,以及他们中间的业务逻辑。 现在使用框架构建前台和后台系统已经成为普遍共识(例如,瓶口溯源码 Struts, Cocoon, Spring, Hibernate, JDO, 和 Entity Beans), 但却没有一个标准的方法来构建业务逻辑。一些框架,城市门户 源码例如 EJB 和 Spring 只在一个高层实现业务逻辑,但对于我们组织逻辑代码没有任何帮助,所以,为什么没有一个框架来替换冗繁,易错的if...then语句呢,这个框架应该和其它前台或后台框架一样,易于配置,valgrind源码下载具有可读性和重用性。下面我们将介绍Drools 规则引擎,这个来解决我们问题的框架。
下面是彗星模块源码一个典型的Java业务逻辑的代码
if ((user.isMemberOf(AdministratorGroup)
&& user.isMemberOf(teleworkerGroup))
|| user.isSuperUser(){
// more checks for specific cases
if((expenseRequest.code().equals("B")
||(expenseRequest.code().equals("A")
&&(totalExpenses<)
&&(bossSignOff> totalExpenses))
&&(deptBudget.notExceeded)) {
//issue payments
} else if {
//check lots of other conditions
}
} else {
// even more business logic
}
这是大多数程序员写业务逻辑的方法,但是有以下的问题:
如果用户有另一个选项,例如("C") ,那么需要修改上面的代码,当代码很长的定位 网页源码时候,修改代码是难于维护的
我们如何保证代码的正确性,这个代码只有程序员能够看到,真正的使用者,业务人员无法看到这个代码
很多应用程序有相同的业务逻辑,如果某个业务改变了,如何保证其他业务逻辑的一致性
业务逻辑能否不合java语言绑定?
业务逻辑能否用其他的脚本语言。
Java下的规则引擎标准就是JSR,它的实现主要有Jess Jena Drools
Drools中,一个典型的业务逻辑的配置,如下
<?xml version="1.0"?>
<rule-set name="BusinessRulesSample"
xmlns="mendPurchase());
}
</java:functions>
<rule-set>
<!-- Ensure stock price is not too high-->
<rule name="Stock Price Low Enough">
<!-- Params to pass to business rule -->
<parameter identifier="stockOffer">
<class>StockOffer</class>
</parameter>
<!-- Conditions or 'Left Hand Side'
(LHS) that must be met for
business rule to fire -->
<!-- note markup -->
<java:condition>
stockOffer.getRecommendPurchase() == null
</java:condition>
<java:condition>
stockOffer.getStockPrice() <
</java:condition>
<!-- What happens when the business
rule is activated -->
<java:consequence>
stockOffer.setRecommendPurchase(
StockOffer.YES);
printStock(stockOffer);
</java:consequence>
</rule>
</rule-set>
一条规则就是rule-set中的rule,如果有很多规则,就要写很多的rule。
上面规则的意思是判断股票价格是否小于,如果这个标准改变了,那么只要修改这个规则文件,而不用去修改源代码了
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- (void) testIsKindOfClass {
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NSLog(@"c1 is a kind of NSObject.");
}
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NSLog(@"c1 is Member of Class1 !");
}
if (![c1 isMemberOfClass:[NSObject class]]) {
NSLog(@"c1 is't Member of NSObject !");
}
}
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