Sunday, March 23, 2014

The Difference between ServletContext and ServletConfig

The servletContext is used to provide configuration that would be available to all servlets in a web application, while servletConfig is used to provide configuration per servlet level.

Specifying and retrieving servletContext configurations.

To specify servletContext configuration, you do so in your web.xml via the <context-param/> tag. For example:


and to retrieve these parameters in any of the defined servlets you have:

String value = getServletContext().getInitParameter("timeout");

Specifying and retrieving servletConfig configurations.

Since servletConfig are available per servlet, the definition is within the servlet definition in the web.xml. This is done using the <init-param/> tag.

    <servlet-name>Polling Servlet</servlet-name>

With this, the specified parameters are only available in the servlet and can be retrieved by:

String value = getServletConfig().getInitParameter("timeout");

Left to me, I would say the not so intuitive choice of words, used to describe these two configuration type, is the cause of confusion most people usually have. I would rather have had the configurations per servlet level called servletConext while configurations that are on the web app level (that are available to all servlet) called appContext or webappContext.

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