How can I know if a viewScope variable has been in

问题:

In an application I need to know if a viewScope variable has been initialized. When the viewScope variable is created the value might be null. So viewScope.isEmpty("SomeName") does not tell me that it has been intialized and the answer is null or it has not been initialized yet. None of the viewScope properties seem to answer the question "dose the viewScope exist".

回答1:

You can get the information whether a viewScope variable does exist or not with

if (viewScope.containsKey("SomeName")) ...