java 参数可以为空的 Freemarker 函数
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Freemarker function with parameter that can be empty
提问by Ula Krukar
I created function in Freemarker:
我在 Freemarker 中创建了函数：
<#function formatDate anyDate>
<#assign dateFormat = read_from_configuration() />
<#if anyDate??>
<#return anyDate?date(dateFormat) />
<#else >
<#return '' />
</#if>
</#function>
I call it like this: ${formatDate(object.someDate)}.
我这样称呼它：${formatDate(object.someDate)}.
It all works until someDateis null. In that case I get exception:
这一切都有效，直到someDate为空。在这种情况下，我得到异常：
Error executing macro: formatDate required parameter: anyDate is not specified.
How can I do this? I want the function to work if parameter values is null.
我怎样才能做到这一点？如果参数值为空，我希望该函数正常工作。
采纳答案by Ula Krukar
In the end I did it like this:
最后我是这样做的：
<#function formatDate anyDate='notSet'>
<#assign dateFormat = read_from_configuration() />
<#if anyDate?is_date>
<#return anyDate?string(dateFormat) />
<#else >
<#return '' />
</#if>
</#function>
回答by Scott Rippey
Here's what I did, which seems to work in most scenarios:
这是我所做的，这似乎在大多数情况下都有效：
The default value should be an empty string, and the null-check should be ?has_content.
默认值应为空字符串，空检查应为?has_content。
<#function someFunction optionalParam="" >
<#if (optionalParam?has_content)>
<#-- NOT NULL -->
<#else>
<#-- NULL -->
</#if>
</#function>
回答by TheYann
Freemarker doesn't really handle the null values very well.
Freemarker 并不能很好地处理空值。
I always use the ?has_content on the params to check if there is something in there. The other parameter checkers don't always handle the null value well either so I would suggest something like this:
我总是使用参数上的 ?has_content 来检查那里是否有东西。其他参数检查器也不总是能很好地处理空值，所以我建议如下：
<#if anyDate?has_content && anyDate?is_date>
just to be sure.
只是要确定。
