Tomcat Tags

Additional tags can be placed in the web.xml file to control the behavior of the web application.

Setting the Default Welcome Page

When a directory is requested from Tomcat, it will look for a default page to display. This page is usually named index.jsp, but it can be changed to any other name by using the welcome-file-list tag. Several welcome files can be defined in the list. 

<welcome-file-list>
  <welcome-file>myFile.jsp</welcome-file>
  <welcome-file>otherFile.jsp</welcome-file>
</welcome-file-list>

Setting a Custom Error Page

Tomcat uses its own default messages for 404 errors and 500 errors. A page of your own choice can be created and displayed instead of the default page by using the error-page tag. Create a separate error-page tag for each error to be redefined. 

<error-page>
  <error-code>500</error-code>
  <location>/myDir/myFile.html</location>
</error-page>

Tomcat does not distinguish amongst all the 400 errors, they are all treated as a 404 error. This means that if there is a file that exists, but has the wrong permissions, then Tomcat will catch that as a 404 error, not a 403 error.

If you are using Internet Explorer, then you need to go to the Advanced Internet Options and uncheck Show Friendly HTTP Error Messages. You may also need to be sure that you error file is larger than a minimum size. I am unable to duplicate this problem, but students report that the problem exists. If your error file is too small, you may still see the friendly error message.

If you have already displayed a default error message and then change to a custom error message, be sure that you clear the cache so that the old error message does not display.

Order of Tags

You must be very careful about where you put these tags in the web.xml file. If they are in the wrong order, then your application will not start.

For more info on the web.xml file you can view the DTD for it: http://java.sun.com/dtd/web-app_2_3.dtd

This is the order of all elements in the web.xml file. The only required element is web-app. If an element is followed by a ?, then it can only appear once. If the element is followed by a *, then it can appear multiple times, but all grouped together. 

web-app (
  icon?, 
  display-name?, 
  description?, 
  distributable?,
  context-param*, 
  filter*, 
  filter-mapping*, 
  listener*, 
  servlet*,
  servlet-mapping*, 
  session-config?, 
  mime-mapping*, 
  welcome-file-list?,
  error-page*, 
  taglib*, 
  resource-env-ref*, 
  resource-ref*, 
  security-constraint*,
  login-config?, 
  security-role*, 
  env-entry*, 
  ejb-ref*,  
  ejb-local-ref*
)