web.xml – Enavigo

Jetty 6 welcome file: how to use a servlet to handle your welcome file

I ‘ported’ my Java web application from Tomcat to Jetty. Like any web application, I defined a ‘welcome file’ in the application’s web.xml file. The welcome-file directive specifies the URL to be loaded by default when someone requests the root of your application. The welcome file may be just a file or a JSP, e.g. index.html, or it may be a name that is mapped to a servlet’s url (through the element in web.xml).

In Tomcat, specifying something like

will work just as you would expect. But in Jetty, it will not. Unless you provide a workaround. What the somewhat angrily written post says is this: If you map a servlet to the URL index.htm, a file called index.htm must still exist. You *must* have a static, even empty, file called index.htm to have Jetty pass the request to your servlet that is mapped to that URL. Sorta cludgy, glad I found the answer quickly. Hope this helps others.

Deploying a web application to Jetty

So you have a Spring MVC web application and want to make sure that when the user enters a URL such as
http://www.myawesomedomain.com he/she will see the home page of your application. How do you get Spring MVC’s RequestDispatcher servlet, which acts as the traffic cop and then some for your web application, to act as the default URL handler in the eyes of the web application? There are two good ways to do it, and two bad ones. Let’s start with the bad ones, of course:

Redirect through meta tag: you add a meta-refresh element to the head element which causes the browser showing the page to go the ‘real’ home page url, such as /index.do
You use JavaScript to force the page to redirect – this will also work but forces you to rely on client-side processes to get stuff done. For example: window.location="index.do" inside an index.html file.

Both are sub-prime because search engines are not too keen to follow such redirects, often time avoiding JavaScript altogether.

So what are the good ways:

Using Apache’s mod-rewrite to mask the URL of your application, but that assumes you have a web server in front of your application
Using the servlet API – which is what you read below

So how do you do it?

In the application’s web.xml file map the RequestDispatcher servlet to handle requests for index.htm, aside from handling the extension of your liking, say, *.do. You do this through the servlet-mapping element. This should look like this:

<servlet -mapping>
    </servlet><servlet -name>requestDispatcher</servlet>
    <url -pattern>*.do</url>
 </servlet -mapping>
  <servlet -mapping>
    </servlet><servlet -name>requestDispatcher</servlet>
    <url -pattern>/index.htm</url>
 </servlet -mapping>

Also in web.xml, set up a welcome file that may be requested by a browser when a user does not enter a specific page request, e.g. www.domain.com. Most browsers at a minimum will automatically request, on behalf of the user, index.html and index.htm.

So choose one, say index.htm and set the <welcome-file> element to look something like this:
<welcome-file-list> <welcome-file>index.htm</welcome-file> </welcome-file-list>
This will make your application by default make requests for ‘/’ go to index.htm.

The last and final step is to map the url index.htm to the controller for the application’s home page. You do this in a Spring MVC beans xml file when specifying the URL mapper.
For example:

<bean id="unAuthenticatedUrlMapping"
        class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="mappings">
      <props>
        <prop key="/index.do">homePageController</prop>
        <prop key="/index.htm">homePageController</prop>
      </props>
    </property>
  </bean>

This way the RequestDispatcher will know which control is actually going to load the information that will be displayed by the view for the home page.

And that’s it. No redirection. No nonsense.