Convert objects in Velocity templates to JSON

VelToJSON

#macro(VelListToJSON $list )
	#set($myList = $list )## dereference
	{
	#foreach($key in $myList.keySet())
		"$key":
		#set($x = $myList.get($key))
		#VelToJSON($x)
		#if($foreachCount != $myList.keySet().size()) , #end
	#end
	}
#end

#macro(VelArrayToJSON $arr)
	#set($myArr = $arr)
	[
	#foreach($x in $myArr)
		#VelToJSON($x)
		#if($foreachCount != $myArr.size()) , #end
	#end
	]
#end

##TODO: Make it not treat numbers as strings
#macro(VelToJSON $item)
	#if($item.keySet())
		#VelListToJSON($item)
	#elseif($item.size())
		#VelArrayToJSON($item)
	#elseif($item == true || $item ==false)
		$item
	#else
		"$item"
	#end
#end

Modified a bit. Now checks for Numbers:

#set ( $obj = '' ) ## dummy object
#set ( $int_class = $obj.class.forName('java.lang.Number') )
#set ( $bool_class = $obj.class.forName('java.lang.Boolean') )
#set ( $string_class = $obj.class.forName('java.lang.String') )
#set ( $map_class = $obj.class.forName('java.util.Map') )
#set ( $list_class = $obj.class.forName('java.util.List') )
#set ( $foreachCount = 10 )

#macro(VelListToJSON $list )
    #set($myList = $list )## dereference
    {
    #foreach($key in $myList.keySet())
        "$key":
        #set($x = $myList.get($key))
        #VelToJSON($x)
        #if($foreachCount != $myList.keySet().size()) , #end
    #end
    }
#end

#macro(VelArrayToJSON $arr)
    #set($myArr = $arr)
    [
    #foreach($x in $myArr)
        #VelToJSON($x)
        #if($foreachCount != $myArr.size()) , #end
    #end
    ]
#end

#macro(VelToJSON $item)
    #if($map_class.isAssignableFrom($item.class))
        #VelListToJSON($item)
    #elseif($list_class.isAssignableFrom($item.class))
        #VelArrayToJSON($item)
    #elseif($bool_class.isAssignableFrom($item.class)|| $int_class.isAssignableFrom($item.class))
        $item
    #else ## $string_class.isAssignableFrom($item.class)
        "$item"
    #end
#end

@mexitek @narenranjit
I'd like to use this, can you license it with the MIT or Apache license, please?

@TheClassic gists don't support notifications :(

you won't get this mention but maybe you'll revisit this topic someday :)

Please note that JSON (like JavaScript) has encoding and escaping rules that will not be followed by this code. So for example, if your strings are allowed to contain characters like " and \, then you have an injection vulnerability. You could make use of the EscapeTool builtin, but you would need to put that on the template context, e.g., $esc.