Dynamically evaluate an el expression

Question

How can I get the value of el expression dynamically in an controller. For eq.

class ElController {
  def index() = {
    def a = "\${1 + 3}"
    unknownElEvaluator(a) // ->"2"
    ....
  }
}

Answer 1

You can do that with the Groovy SimpleTemplateEngine:

import groovy.text.SimpleTemplateEngine

def binding = [:]
def a = "\${1 + 3}"
String rslt = new SimpleTemplateEngine().createTemplate( a )
                                        .make( binding )
                                        .toString()
assert rslt == '4' // 4 not 2 as in your question

Though it would be interesting to know why you'd be doing this in a controller...

Alternatively, you should be able to add:

def groovyPagesTemplateEngine

To your controller (or preferably as separate Service class, as you may end up wanting to do this from more than one place in your code)

Then, from inside the method, do:

def binding = [:]
def a = "\${1 + 3}"

String rslt = new StringWriter().with { writer ->
  groovyPagesTemplateEngine.createTemplate( a, 'myscript' )
                           .make( binding )
                           .writeTo( writer )
  writer.toString()
}