Unsetting a variable in Velocity

java templates velocity
Simon Nickerson picture Simon Nickerson · Mar 18, 2009 · Viewed 14.9k times · Source

Is it possible to set a Velocity reference to 'null' or 'undefined'?

The Velocity template language reference says

#set - Establishes the value of a reference Format:

# [ { ] set [ } ] ( $ref = [ ", ' ]arg[ ", ' ] )

Usage:

$ref - The LHS of the assignment must be a variable reference or a property reference.

arg - The RHS of the assignment, arg is parsed if enclosed in double quotes, and not parsed if enclosed in single quotes. If the RHS evaluates to null, it is not assigned to the LHS. (emphasis mine)

I cannot find an equivalent #unset macro.

Answer

Merzbow picture Merzbow · Mar 18, 2009

You can set the reference to false. As a non null reference is considered true, you can then test if the reference is set. This is useful in loops.

#foreach ($obj in $list)
#set ($x = false)
#set ($x = $obj.maybeNull())
#if ($x)
...
$x
#end
#end

Related questions

How to use 'for' loop in velocity template?

I just googled for 'for loop', but it looks like velocity has 'foreach' only. How do I use 'for loop' in velocity template?

Read More
How to access/get the size of an array/collection in velocity templates?

I am using velocity for email templates in my java/spring 3 app. How could I get the size of an ArrayList added to the model from within the template.

Read More
Velocity nulls and empty strings

In velocity I have a variable which its value is null. I don't want to display anything in that case. Currently the template engine translates "" to null so I have to do. #set ( $a = "") #if ($a) assert("never prints a …

Read More