Converting velocity response to JSON - json

Question

I am using struts 2 and velocity templates to generate JSON response.
Now the catch is the response is not generated using some velocity JSON plugin
it's just a String that comes out once velocity is done with its parsing and rendering of
response, and on client side I do eval to get the response from string to JSON.
What I really need is some solution on velocity's or struts' side where, once the result is
generated by velocity, the framework should call my API where I can convert the response output of vm file into JSON using my own logic. How do achieve this?
For example:
On browser using JavaScript I have designed a tree widget that I use for displaying comments in tree structure.
Say user clicks on comments button.
My UI widget will fire an AJAX to get data for comments.
This request is intercepted by STRUTS 2 framework.
It will call, say, getComments() action API and will populate an arrayList with comment object say cmt.
Now the response is handled by a velocity template(*.vm).
Now in vm I am writing code like this:
{ "CommentsData" : [
#set($sep="")
#foreach($c in $cmt)
$sep
{
"commentText" : $c.getText()
}
#set($sep=",")
#end
}
Now the final response may turn out like this:
{ "CommentsData" : [
{
"commentText" : "This is comment 1"
},
{
"commentText" : "This is comment 2"
},
{
"commentText" : "This is comment 3"
},
{
"commentText" : "This is comment 4"
}`
]
}
Now this may look like JSON, but its not strict JSON; I mean if I miss
some , somewhere then on client side in JavaScript my eval might fail or JSON.parse()
will fail, but on velocity template I have now clue if JSON is malformed.
So once the above velocity template is generated I need some control, where I can write some Java code to do some validations on the response.
I see that my approach to use velocity template to generate JSON output (actully a String that looks like JSON) may be wrong. But still I need to handle the response of every velocity template I have written.

Answer 1

Not sure how you are using velocity. We don't use velocity when outputting JSON; we just create a JSON convertible object and output it directly from controllers using response.write(jsonObject.toJson()). This way, proper JSON is always generated.