In this little blogpost, I’ll try to explain the differences between ServletConfig and ServletContext and when you can use them into a Java Web Application.

ServletConfig

ServletConfig is actually very simple. Like stated above, you can retrieve parameters for the servlet which are set at deployment time.
I’ll explain this with a very simple example.

If you have created a servlet with the name “MyServlet” you can add the following 2 variables into the servlet:

    <servlet>
         <servlet-name>MyServlet</servlet-name>
         <servlet-class>servlets.MyServlet</servlet-class>
         <init-param>
             <param-name>variable1</param-name>
             <param-value>I'm var1</param-value>
         </init-param>
         <init-param>
             <param-name>variable2</param-name>
             <param-value>I'm var2</param-value>
         </init-param>
     </servlet>
     <servlet-mapping>
         <servlet-name>MyServlet</servlet-name>
         <url-pattern>/MyServlet</url-pattern>
     </servlet-mapping>

You can retrieve variable2 with the following code:

getServletConfig().getInitParameter("variable2");

Retrieve all the variables of the servlet and loop over them:

Enumeration allvars = getServletConfig().getInitParameterNames();
while (allvars.hasMoreElements()) {
     String next = (String) allvars.nextElement();
     out.println(next + " has the value " + getServletConfig().getInitParameter(next));
}

It’s also possible to retrieve the servlets name through getServletconfig

out.println("The name of the servlet is: " + getServletConfig().getServletName());

ServletContext

ServletContext can be used to retrieve application-wide parameters, get serverparameters and store/retrieve/remove application-wide attributes.

It is possible to call the ServletContext right on or through the ServletConfig. Both are the same so you can choose between them.

if (getServletContext().equals(getServletConfig().getServletContext())) {
       out.println("both calls retrieve the same Context");
}

Just like with ServletConfig, you can set parameters in the Deployment Descriptor. They are initialized on compile time. It’s not possible to remove or add them on runtime.

<context-param>
        <param-name>variable3</param-name>
        <param-value>Im var 3</param-value>
</context-param>

And call them in your servlet just like the ServletConfig parameters:

getServletContext().getInitParameter("variable3")

Unlike ServletConfig, ServletContext can work with attributes. These are parameters or objects which you can set into the servlet and retrieve in every other servlet of your Web Application:

getServletContext().setAttribute("test", "I'm an application-wide String");
..
out.println(getServletContext().getAttribute("test"));
..
getServletContext().removeAttribute("test");

I’ll end this little short tutorial with an example of how you can retrieve serversettings through the Context:

out.println(getServletContext().getContextPath());
out.println(getServletContext().getMajorVersion());
out.println(getServletContext().getRealPath(""));
out.println(getServletContext().getServerInfo());

If there are any more questions, just shoot them

In most of the cases, there is more than just one website on a server.
Though, it is very important that you can measure the stats of all the websites separately.
I’ll tell you in a few lines how you can achieve this with webalizer.

This tutorial is tested with Webalizer on Ubunty but I presume it will work almost the same way in other distros.

First of all you have to install webalizer on your system.

sudo apt-get install webalizer

After installation of webalizer, the configurationfiles are per default stored in /etc/webalizer.
Move to that directory and make a copy of the config-file.

sudo cp webalizer.conf MySiteName.conf

When the copy is created you have to open it in your favorite editor (I use vim)

sudo vim MySiteName.conf

Scroll down till you find the LogFileattribute and change it to the accesslogfile of MySiteName.
You also have to tell the script where the outputfiles will be stored. This is normally a place which is accessible by the browser.

LogFile /www/mysite/logs/access.log
OutputDir /www/mysite/public_html/webalizer

These are the only 2 parameters which you have to change. You can scroll through the rest of the file and make changes towards your preferences.

All is done now so you can run webalizer with the new configuration file

webalizer -c /etc/webalizer/MySiteName.conf

Webalizer will run and should be accessible through your webbrowser.
Obviously, it would kinda suck if you have to run the webalizerscript every time you want to see the stats so we gonna make a cron which will run the script every hour

crontab -e

And fill in:

0 * * * * webalizer -c /etc/webalizer/MySiteName.conf

Voila, all done