Different behaviour on servlet w/o servlet-mapping and init parameters

Question

I was playing around and found, that the init-parameter of a servlet is always null if there is no servlet mapping. I did not define a servlet mapping because I used the servlet only for for (named) dispatching (client usage should not be allowed).
web.xml:
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4">
  <servlet>
    <servlet-name>InitParamServlet</servlet-name>
    <servlet-class>test.InitParamServlet</servlet-class>
    <init-param>
      <param-name>param1</param-name>
      <param-value>value1</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>InitParamServlet</servlet-name>
    <url-pattern>*.initparam</url-pattern>
  </servlet-mapping>
</web-app>
InitParamServlet.java:
package test;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class InitParamServlet extends HttpServlet{
  private static final long serialVersionUID = 1L;
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter pw = response.getWriter();
    pw.write(getServletName());
    pw.write(": param1=" + getInitParameter("param1"));
}The URL http://localhost:8080/xxx/servlet/test.InitParamServletreturns org.apache.catalina.INVOKER.test.InitParamServlet: param1=null
(on Tomcat), and the call to the same servlet with URL http://localhost:8080/xxx/test.initparamreturns InitParamServlet: param1=value1 instead (the correct init parameter value)!
The same happens with jetty. This looks strange for me; I would expect the same behaviour for the servlet (independent from servlet-mapping-tag in the web.xml).

Answer 1

When you call the url
http://localhost:8080/xxx/servlet/test.InitParamServlet
you are actually calling the invoker servlet that is defined in the default conf/web.xml. If you look at this web.xml file you will see that the invoker is mapped with the pattern "/servlet/*" which maps to the above url. The request goes to this servlet which parses the url and then calls the InitParamServlet class.
When you call the url
http://localhost:8080/xxx/test.initparam
you are matching the url pattern you defined in the WEB-INF/web.xml file ("*.initparam"). This time the request goes to servlet instance that you defines in the servlet naming tags as "InitParamServlet" and since you defined init params they are populated.
Note that these urls will also match the "*.initparam" pattern
http://localhost:8080/xxx/XXXXX.initparam
http://localhost:8080/xxx/badpackage.initparam
http://localhost:8080/xxx/A.initparam
Most people would have simplely defined the second servlet mapping as "initparam" and accessed the servlet with the url
http://localhost:8080/xxx/initparam