Calling a default servlet first in Java web application

Question

Hi,

I wand my SampleServlet to called first whenever my java web application is accessed in this manner : http://server:8080/appname/

Is there any way to implement this?

Thanks, Veera.

Answer 1

Not sure what you mean but you need to map your servlet to "/"

<servlet-mapping>
    <servlet-name>SampleServlet</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

Answer 2

Not sure what is your aim, but web application initialization can be achieved by ServletContextListener:

public class AppListener implements ServletContextListener {
    public void contextInitialized(ServletContextEvent event) {
        // place your code here
    }

    public void contextDestroyed(ServletContextEvent event) {
    }
}

and later in web.xml:

<web-app>
<listener>
    <listener-class>
        package.AppListener
    </listener-class>
</listener>
...
</web-app>

Answer 3

I think a filter would be more appropriate. See http://java.sun.com/products/servlet/Filters.html.

Answer 4

If you want to make a servlet your homepage then this worked for me on http://feelitlive.com/

<welcome-file-list>
 <welcome-file>homepage</welcome-file>
</welcome-file-list>

...

<servlet>
 <description>Shows stuff on the homepage</description>
 <display-name>Homepage Servlet</display-name>
 <servlet-name>HomepageServlet</servlet-name>  
 <servlet-class>com.cantorva.gigcalendar.servlets.HomepageServlet</servlet-class>
</servlet>

...

<servlet-mapping>
 <servlet-name>HomepageServlet</servlet-name>
 <url-pattern>/homepage</url-pattern>
</servlet-mapping>

That means that that users arriving at your application via the URL you specified will be welcomed by your servlet. It also creates an alias for the homepage at "/homepage" but you don't have to use that.

If you want to run some code on start-up then asalamon74's answer looks right.

Answer 5

If you want to run code on start-up indeed asalamon74's answer should be fine. If you have a legacy situation and you must use a servlet, the parameter load-on-startup can do the trick for you:

<servlet>
    <servlet-name>SampleServlet</servlet-name>
    <display-name>SampleServlet</display-name>
    <description>Sample Servlet</description>
    <servlet-class>...</servlet-class>
    <init-param>...</init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

The load-on-startup tag specifies that the servlet should be loaded automatically when the web application is started; the number value just gives a loading order to those loading on startup. If no value is specified, the servlet will be loaded when the container decides it needs to be loaded - typically on it's first access.