FreeMarker has_content等价于StringUtils.isNotNullOrEmpty

has_content

It is

true

if the variable exists (and isn't Java

null

) and is not "empty", otherwise it is

false

. The meaning of "empty" depends on the concrete case. This follows intuitive common-sense ideas. The following are empty: a string with 0 length, a markup output value with 0 length markup, a sequence or hash with no sub variables, a collection which has passed the last element. If the value is not of any of these types, then it counts as non-empty if it's a number or a date or a boolean (e.g.

0

and

false

are not empty), otherwise it counts as empty. Note that when your data-model implements multiple template model interfaces you may get unexpected results. However, when in doubt you can use always use

expr!?size > 0

or

expr!?length > 0

instead of

expr?has_content

.

This buit-in is exceptional in that you can use the parentheses trick like with the default value operator. That is, you can write both

product.color?has_content

and

(product.color)?has_content

. The first doesn't handle the case when

product

is missing, the last does.