Java $null 检查速度
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$null check in velocity
提问by lucky
I came to know about null check using $null in velocity 1.6 through a resource updated by you. Resource: Reading model objects mapped in Velocity TemplatesBut I am facing so many challenges that there is no $null for null check in velocity as there is no documentation provided about this. Please provide me with documentation stating $null as valid for null check in velocity.
我通过您更新的资源了解了在 Velocity 1.6 中使用 $null 进行空检查。资源：读取映射到 Velocity 模板中的模型对象但我面临着如此多的挑战，以至于没有 $null 用于在 Velocity 中检查空值，因为没有提供关于此的文档。请向我提供说明 $null 对空值检查有效的文档。
Thanks in Advance lucky
提前致谢 幸运
回答by a_horse_with_no_name
To check if a variable is not null simply use #if ($variable)
要检查变量是否为空，只需使用 #if ($variable)
#if ($variable) ... do stuff here if the variable is not null #end
If you need to do stuff if the variable is null simply negate the test
如果您需要在变量为空的情况下做一些事情，只需否定测试
#if (!$variable) ... do stuff here if the variable is null #end
