logic:present

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<logic:present />

The <logic:present /> tag evaluates its body if the variable specified by any one of the cookie, header, name, parameter, or property attributes is present in the applicable scope. The <logic:present /> tag has a body type of JSP and supports eight attributes, described in Table 18.13.

Table 18.13: <logic:present /> Tag Attributes

Attribute	Description
cookie	Specifies an HTTP cookie to be used as the variable being tested for existence. (Optional)
header	Specifies a case-insensitive HTTP header to be used as the variable being tested for existence. (Optional)
name	Defines a scripting variable to be used as the variable being tested for existence. (Optional)
property	Specifies the data member of the scripting variable to be tested. (Optional)
parameter	Specifies an HTTP parameter to be used as the variable being tested for existence. (Optional)
scope	Defines the scope of the bean specified by the name attribute. If the scope attribute is not specified, then the tag will search for the bean in the scopes, in the order of page, request, session, and application. (Optional)
role	Used to determine if the currently authenticated user belongs to one or more named roles. If more than one role is listed, then they must be separated by commas. (Optional)
user	Used to determine if the currently authenticated user has the specified name. (Optional)

An example of using the <logic:present /> tag is shown here:

 <logic:present parameter="username">   Welcome <%= username %>. </logic:present > 

In this example, we test for the existence of the request parameter username. If the username parameter is part of the request, then the tag's body will be evaluated.

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