JavaServer Pages, 3rd Edition

Setting and Using Configuration Variables

Some of the JSTL tag libraries use default values for attributes that are not specified explicitly in the action elements, e.g., the data source to be used by the database actions and the locale used by the I18N actions. As I described in Part II, you can set these default values using context parameters in the deployment descriptor, but you can also set them dynamically using a servlet, filter, or listener. A typical example is a filter or a servlet that sets the locale based on user profile information. The term used for the dynamic settings in the JSTL spec is configuration variables, and when combined with a context parameter, it’s called a configuration setting.

Each configuration setting is identified by a unique name, such as javax.servlet.jsp.jstl.fmt.locale for the default locale. This is the name you use when you set a default value through a context parameter:

<web-app ...>
  ...
  <context-param>
    <param-name>
      javax.servlet.jsp.jstl.fmt.locale
    </param-name>
    <param-value>
      en-US
    </param-value>
  </context-param>
  ...
</web-app>

The same names are used to set, read, and remove the configuration variables programmatically, using a JSTL class called javax.servlet.jsp.jstl.core.Config. It has the following fields:

public static final String FMT_LOCALE = "javax.servlet.jsp.jstl.fmt.locale"; public static final String FMT_FALLBACK_LOCALE = "javax.servlet.jsp.jstl.fmt.fallbackLocale"; public static final String FMT_LOCALIZATION_CONTEXT = "javax.servlet.jsp.jstl.fmt.localizationContext"; ...