英文:
Java based simple rule engine with fallback
问题
我需要实现一个带有分层回退支持的简单规则引擎。我已经研究过DROOLS库,但我不确定它是否支持我的用例。
用例相当简单,这让我在思考是否需要规则引擎?尽管如此,以下是用例 -
我有一个带有一堆字段的模型
Public Class Entity {
public int val0;
public int val1;
public int val2;
public int val3;
.....
}
现在,我想针对这些字段创建以下规则
RULE1 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == 1 --- (1,1,1,1) THEN DO this
RULE2 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == 2, --- (1,1,1,2) THEN DO this
RULE3 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == *, --- (1,1,1,*) THEN DO this
RULE4 --- IF val0 == 1 && val1 == 1 && val2 == * && val3 == *, --- (1,1,*,*) THEN DO this
问题出现在RULE3
和RULE4
,其中val2和val3可以匹配任何值。
例如
val0=1,val1=1,val2=1,val3=1 -- 应执行RULE1 - 具体匹配
val0=1,val1=1,val2=1,val3=3 -- 应执行RULE3 - 由于val3没有特定的匹配,因此为通用匹配
val0=1,val1=1,val2=10,val3=5 -- 应执行RULE4 - 由于val2和val3没有特定的匹配,因此为通用匹配
因此,根据查询,我要么会找到匹配的规则,要么必须回退到更通用的规则。是否存在现有的规则引擎库提供此功能,或者是否我甚至需要规则引擎库来实现此功能?
英文:
I need to implement a simple rules engine with hierarchical fallback support. I have already looked into the DROOLS library but I am not sure if it supports my use case.
The use case is rather simple which makes me thinking whether I need a rules engine at all? Nevertheless, here is the use case -
I have a modal with bunch of fields
Public Class Entity {
public int val0;
public int val1;
public int val2;
public int val3;
.....
}
Now, I want to create rules against these fields as follow
RULE1 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == 1 --- (1,1,1,1) THEN DO this
RULE2 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == 2, --- (1,1,1,2) THEN DO this
RULE3 --- IF val0 == 1 && val1 == 1 && val2 == 1 && val3 == *, --- (1,1,1,*) THEN DO this
RULE4 --- IF val0 == 1 && val1 == 1 && val2 == * && val3 == *, --- (1,1,*,*) THEN DO this
The problem is with RULE3
and RULE4
where val2 and val3 can match any value.
e.g.
val0=1, val1=1, val2=1, val3=1 -- should execute RULE1 - specific match
val0=1, val1=1, val2=1, val3=3 -- should execute RULE3 - generic match as there's no specific match for val3
val0=1, val1=1, val2=10, val3=5 -- should execute RULE4 - generic match as there's no specific match for val2 and val3
So depending on the query, either I will find the matching rule or I will have to fallback to the more generic rules. Is there any existing rules engine library that provides this functionality or rather do I even need a rules engine library to implement this functionality?
答案1
得分: 2
起初我认为你可能想考虑使用位逻辑,但由于某些字段采用非二进制值,这对你可能没有实际作用。
然而,解决方案不必太复杂。只需创建一个类,作为Entity
值的匹配器,并使用一系列的if-else语句来寻找匹配项。
class EntityMatcher {
private Integer val0, val1, val2, val3;
/** 用于匹配所有参数的构造函数 */
EntityMatcher(int val0, int val1, int val2, int val3) {
// 设置字段 0-3
}
/** 当不关心 val2 和 val3 时使用的构造函数 */
EntityMatcher(int val0, int val1) {
// 设置字段 0 和 1,将 val2 和 val3 设置为 null
}
boolean matches(Entity toMatchAgainst) {
return (this.val0 == null || this.val0 == toMatchAgainst.val0)
&& (this.val1 == null || this.val1 == toMatchAgainst.val1)
...
&& (this.valN == null || this.valN == toMatchAgainst.valN);
}
}
然后你的规则引擎可能看起来像这样:
if (new EntityMatcher(1, 1, 1, 1).matches(entity))
// 规则 1
else if (new EntityMatcher(1, 1, 1, 2).matches(entity))
// 规则 2
...
else if (new EntityMatcher(1, 1).matches(entity))
// 规则 4
...
else
// 没有匹配项
这本质上与Scala中的case类相同。
英文:
At first I thought you might want to consider using bitwise logic, but with some of the fields taking non-binary values this probably doesn't really work for you.
However, the solution needn't be that complicated. Just create a class that acts as a matcher for the values of Entity
and use a chain of if-else statements to find the match.
class EntityMatcher {
private Integer val0, val1, val2, val3;
/** Constructor used to match all the parameters */
EntityMatcher(int val0, int val1, int val2, int val3) {
// set fields 0-3
}
/** Constructor used when you don't care about val2 & val3 */
EntityMatcher(int val0, int val1) {
// set fields 0 & 1, leaving val2 and val3 as null
}
boolean matches(Entity toMatchAgainst) {
return (this.val0 == null || this.val0 == toMatchAgainst.val0)
&& (this.val1 == null || this.val1 == toMatchAgainst.val1)
...
&& (this.valN == null || this.valN == toMatchAgainst.valN);
}
}
Then your rules engine could look something like this:
if (new EntityMatcher(1, 1, 1, 1).matches(entity))
// Rule 1
else if (new EntityMatcher(1, 1, 1, 2).matches(entity))
// Rule 2
...
else if (new EntityMatcher(1, 1).matches(entity))
// Rule 4
...
else
// no match
This is essentially the same idea as case classes in Scala.
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