String Data Type Gotcha When Using CFGroovy
Posted September 14, 2009 at 10:19 AM
I just started playing around with Barney Boisvert's CFGroovy (2) Groovy script engine for ColdFusion. I attended Barney's CFUNITED presentation and was truly inspired; not only is Barney a ridiculously bright guy, this CFGroovy stuff looks really cool.
I downloaded his scripts, starting playing, and within five minutes, I ran into my first rub when dealing with string values. Take a look at this simple example:
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- <!--- Import the CFGroovy tag library. --->
- <cfimport prefix="g" taglib="./cfgroovy/" />
-
- <g:script>
-
- <!---
- Store a message into the variables scope.
-
- NOTE: The variables scope is one of the implicit scopes
- that is automatically bound to the groovy context.
- --->
- variables.message = "Hello Ben!";
-
- </g:script>
-
- <!---
- Output the message. Check to make sure that the value is
- simple so that we can use the hash evaluation.
- --->
- <cfif isSimpleValue( variables.message )>
-
- <cfoutput>
- #message#
- </cfoutput>
-
- </cfif>
Here, I am simply setting a message value into the Variables scope from within the Groovy context. Then, I am outputting the message. Notice that once I am back in the ColdFusion context, I don't have to scope the value since the Variables scope is the implied scope for unscoped values. Anyway, this runs perfectly well, outputting:
Hello Ben!
Much like the hash signs (#) in ColdFusion, Groovy also allows variable substitution in strings using the ($) sign. To play with this, I tried the following, simple example:
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- <!--- Import the CFGroovy tag library. --->
- <cfimport prefix="g" taglib="./cfgroovy/" />
-
- <g:script>
-
- <!--- Store a groovy-local variable for the name. --->
- def name = "Ben";
-
- <!---
- Store a message into the variables scope. This time, we
- are going to substitute the name variable into the message
- that we are storing.
-
- NOTE: Groovy uses "$" to denote variables.
- --->
- variables.message = "Hello $name!";
-
- </g:script>
-
- <!---
- Output the message. Check to make sure that the value is
- simple so that we can use the hash evaluation.
- --->
- <cfif isSimpleValue( variables.message )>
-
- <cfoutput>
- #message#
- </cfoutput>
-
- </cfif>
This time, however, nothing was output to screen. It seems that for some reason, the message being stored now is no longer a simple value. After doing some CFDumping of values, I discovered that the message variable, this time, was the Groovy class:
org.codehaus.groovy.runtime.GStringImpl
Apparently, because we are doing a variable substitution, rather than creating a string directly, Groovy creates an internal string representation object which contains a list of values that can eventually be combined to represent the final string. To get around this, I simply had to merge the values back into a single string using the toString() method:
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- <!--- Import the CFGroovy tag library. --->
- <cfimport prefix="g" taglib="./cfgroovy/" />
-
- <g:script>
-
- <!--- Store a groovy-local variable for the name. --->
- def name = "Ben";
-
- <!---
- Store a message into the variables scope. This time, we
- are going to substitute the name variable into the message
- that we are storing.
-
- NOTE: Groovy uses "$" to denote variables.
-
- NOTE: Because we are using variable substitution, this
- creates a complex string representation which we have to
- explicitly convert back to string.
- --->
- variables.message = ("Hello $name!").toString();
-
- </g:script>
-
- <!---
- Output the message. Check to make sure that the value is
- simple so that we can use the hash evaluation.
- --->
- <cfif isSimpleValue( variables.message )>
-
- <cfoutput>
- #message#
- </cfoutput>
-
- </cfif>
This time, when we run the code, we get the expected output:
Hello Ben!
Because this object, GStringImpl, has a toString() method, ColdFusion is smart enough to know that it can try to turn it into a string when it has to do string manipulation (much like it can implicitly cast XML documents to string). As such, the second code example above only failed because of the IsSimpleValue() method call. Had we simply tried to evaluate the Variables.Message value using hash tags, it would have worked properly.
From what I saw Barney do with the Groovy engine, it looks there is a lot of possibility here. Definitely worth exploring.
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Reader Comments
Looks like you got hung up by a GString, huh?
@Tony,
Ha ha - you always think it's gonna be fun... till it happens to you.
Yes it's crucial to understand that Groovy Strings (GStrings) are not Strings. They are a separate class that does lazy initialization of the variables within it. That means that until toString() is called, the value isn't evaluated and transformed into a String.
You can see more here, in particular the section "GStrings Are Not Strings": http://groovy.codehaus.org/Strings+and+GString
A problem I ran into is "null" values being passed back to ColdFusion from Groovy. I found you can just do a Len( propWithNull ) to check for it, but it just required some more testing before display on what value was actually stored in the property. Haven't really had to deal with NULL values in CF much up to this point.
@Gareth, @Brian,
Good tips. Thanks.
