Invoking a java class while server start up

Question

Hi,
I want to invoke a java class/method immediately after a web server is started. Can any body tell me how to do this.
Regards,
Prakash

Answer 1

It is easy.
Write a serlvet, lets call it ConfigServlet that handles the configuration parameters of a web-application.
My GenericConfigServlet looks like this:
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.log4j.Logger;
public class GenericConfigServlet extends HttpServlet
     private static final long serialVersionUID = 1L;
     public void init(ServletConfig config) throws ServletException
          super.init(config);
          ServletContext sCtx = getServletContext();
          ServletConfig sCfg = getServletConfig();
            String prefix =  sCtx.getRealPath("/");
            synchronized (this)
               Enumeration initParams = sCfg.getInitParameterNames();
               String key, value;
               GenericConfigProperties.setApplicationBasePath(prefix);
               while (initParams.hasMoreElements()) {
                    key = (String) initParams.nextElement();
                    value = sCfg.getInitParameter(key);
                    GenericConfigProperties.setProperty(key,value);
}Then in your web.xml, you write like this:
<servlet-name>ConfigServlet</servlet-name>
          <servlet-class>GenericConfigServlet</servlet-class>
          <init-param>
               <param-name>LICENSES</param-name>
               <param-value>1</param-value>
          </init-param>
          <init-param>
               <param-name>TMP_DIRECTORY</param-name>
               <param-value>C:\\temp\\</param-value>
          </init-param>
          <init-param>
               <param-name>INPUTFILE</param-name>
               <param-value>C:\\temp\\_input.txt</param-value>
          </init-param>
          <load-on-startup>0</load-on-startup>
     </servlet>You can add any number of init-param-tags.
The important thing is the element <load-on-startup>0</load-on-startup>. This tells the webserver to load this servlet first. A lower number is loades before a higher so if you have a servlet that you want to load but you need the configuration to be done first, that servlet definition should read <load-on-startup>1</load-on-startup>.
Of course, you can do anything you want in the init-method. This is just one way of doing it.
Message was edited by:
Lajm
Additionals...
Message was edited by:
Lajm
Hideing company name... ;-)