java - 取消设置 Velocity 中的变量

Question

是否可以将 Velocity 引用设置为“null”或“undefined”？

Velocity template language reference说

#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)

我找不到等效的 #unset 宏。

Answer 1

您可以将引用设置为 false。由于非空引用被认为是真实的，因此您可以测试是否设置了引用。这在循环中很有用。

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