Freemarker: Dynamic interpolation of sub variables

问题:

I am trying to create a FreeMarker macro that can return the interpolation of a concatenation of a string and the input variable:

<#macro findValue var>
   <#if (.vars["foo." + var]) ??> 
     .vars["foo." + var]
   <#else>
     ${.vars["bar." + var]}
   </#if>
</#macro>

Unfortunately it doesn't work. Firstly, ${.vars["bar." + var]} gives an undefined error. Secondly, the if condition always returns false even when I can see that the sub variable do exist. It seems like the .vars variable can only look up root variables, but not sub variables like foo.test.

回答1:

In FreeMarker, foo.bar is the same as foo["bar"], but inside the [] you can have an arbitrary expression that evaluates to a string. So the expression you are looking for is simply foo[var].

BTW, what your macro tries to do is just ${foo[var]!bar[var]}