basic A/B Testing support, though a percentile value

[credmond-git]

Support some form of dynamic property that depending on a percentile will give a different result each time it is called.

Possible
feature.enabled=${percent:10=true:=false}
feature.value=${percent:10=A,20=B,60=C:=F}

The lowest value that is greater than the percent rolled is selected.
The value should not be cached, and re-rolled each time.

We may want to use a different delimiter than ${} as the ${} represents a value that is computed at load time. Where as this is computed at run time.

[credmond-git]

We need to differentiate between immediate evaluation at load time and deferred evaluation when getting the configuration.

https://jakarta.ee/specifications/expression-language/6.0/jakarta-expression-language-spec-6.0#eval-expressions

the ${expr} construct for immediate evaluation and the #{expr} construct for deferred evaluation. This difference in delimiters points out the semantic differences between the two expression types in the Jakarta EE web tier. Expressions delimited by #{} are said to use “deferred evaluation” because the expression is not evaluated until its value is needed by the system. Expressions delimited by ${} are said to use “immediate evaluation” because the expression is compiled when the JSP page is compiled and it is executed when the JSP page is executed. More on this in Section 1.2.4, “Syntax restrictions”.