evaluating value of an expression as expression in groovy - groovy

Question

Here is the code i am trying to get working
def expr = ''
List params = []
params << 'filter-name'
params << 'servlet-name'
params << 'url-pattern'
params.each{expr = expr+ "it.'${it}'.text().trim()#"}
expr = expr.substring(0, expr.length()-1)
consNodes.each{
println "data is:$"{expr}"
println "actual : ${it.'filter-name'.text().trim()}#${it.'servlet-name'.text().trim()}#${it.'url-pattern'.text().trim()}"
}
in the above result comes like
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : presenceLogoutFilter##/adfAuthentication/*
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : remoteApplication##/rr/*
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : ServletADFContextFilter#GetHandler#
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : ServletADFContextFilter##/PresenceServlet/*
So, as you can see that my constructed expression is not able to evaluate further. Any advise on how to make it work?

Answer 1

The problem is that you're creating a GString like this: "it.'${it}'.text().trim()#", but then you're converting it into a String when you concatenate it: expr + "it.'${it}'.text().trim()#". Once you turn a GString into a String it no longer evaluates expressions. But even if you address that it won't solve your problem because GStrings do not evaluate like you think they do. The best way to explain it is with an example:
import org.codehaus.groovy.runtime.GStringImpl
// What you're doing
def a = 'John'
def b = 'Hello, $a'
def c = "${a}"
assert b == 'Hello, $a'
// What the compiler is doing (ignoring the variable name changes)
def aa = 'John'
def bb = 'Hello, $a'
def cc = new GStringImpl([] as Object[], ['Hello, $a'] as String[])
assert cc == 'Hello, $a'
// What you want the compiler to do, but it will not.
def aaa = 'John'
def bbb = 'Hello, $a'
def ccc = new GStringImpl(['John'] as Object[], ['Hello, '] as String[])
assert ccc == 'Hello, John'
If you really want to, you can build the GStrings manually, but that will be very difficult. And you'd end up depending on a class which is not guaranteed to remain backward-compatible between Groovy releases.
Here's what you can do instead:
def params = []
params << 'filter-name'
params << 'servlet-name'
params << 'url-pattern'
def evaluators = params.collect {
{ attr, node -> node[attr]?.text()?.trim() ?: '' }.curry(it)
}
consNodes.each { node ->
println evaluators.collect { c -> c(node) }.join('#')
}
The output looks like this:
presenceLogoutFilter##/adfAuthentication/*
remoteApplication##/rr/*
ServletADFContextFilter#GetHandler#
ServletADFContextFilter##/PresenceServlet/*
Instead of a single large expression you and up with a list of closures, each responsible for evaluating a node attribute. Then, you can join the results with '#'s.