I have a json template as below:

{
    "firstname": "${fname}"
}

When fname is null, I want to have the value as null instead of a string null ("null"). Hence, I'm expecting the final json to be like:

{
    "firstname": null
}

But, I'm getting:

{
    "firstname": "null"
}

Is there any way we can achieve this using Apache Freemarker? I'm pretty new to Freemarker and couldn't get a precise solution.

CodePudding user response：

You could use #if or ?then, and then ?? operator to check if the value is null, but that's verbose. So instead, move the logic into a #function (or into a Java utility method that you expose):

<#macro nullMarker></#macro>
<#function jsonString s=nullMarker><#return s?is_macro?then('null', '"${s}"')></#function>

I had to do some ugly hack above, as for a function argument that's null there must be default value. So I can't simply use s?? inside the function, as s inside the function will never be null. So instead, I specified a default value that you surely normally don't want to print as JSON. So now you can do this:

${jsonString(fname)}