We start by looking at servlets with sessions. 

I start by creating a new context (a folder in webapps). 

So I can do it like this: 

1.   mkdir $CATALINA_HOME/webapps/0414
2.   mkdir $CATALINA_HOME/webapps/0414/WEB-INF
3.   mkdir $CATALINA_HOME/webapps/0414/WEB-INF/classes
4.   mkdir $CATALINA_HOME/webapps/0414/WEB-INF/lib

5.   pico $CATALINA_HOME/webapps/0414/index.html

Then I check in person:

-bash-3.2$ pwd
/u/dgerman/apache-tomcat-5.5.17/webapps/0414
-bash-3.2$ du -a .
8       ./WEB-INF/lib
8       ./WEB-INF/classes
24      ./WEB-INF
8       ./index.html
40      .
-bash-3.2$ 

I can't remember my port number. Where do I look? 

-bash-3.2$ pwd
/u/dgerman/apache-tomcat-5.5.17/webapps/0414
-bash-3.2$ grep 470 ../../conf/*
../../conf/server.xml:<Server port="47065" shutdown="SHUTDOWN">
../../conf/server.xml:    <Connector port="47064" />
-bash-3.2$ 

Now I know I can access my new context like this: 

http://silo.cs.indiana.edu:47064/0414/

The other way was with Tomcat Manager, set up with tomcat-users.xml file. 

So now I need to get started writing a servlet. 

So what am I looking at: 

a) I will write a file One.java
b) I will place it in classes
c) I will compile it with javac
d) I will remember that that might be version 1.6 
e) so I will be careful to compile with $JAVA_HOME/bin/javac not just javac
f) I will describe it in a web.xml file
  - here I can explicitly state how the user will call the servlet
  - there are three names: 
     1) what the user calls the servlet (nameOne)
     2) what we (the designers) call the servlet internally (nameTwo)
     3) the class name (One)
  - they can be all of them the same (in which case nameOne is One).
g) I will place that file in WEB-INF
h) I will access it as follows: 

   http://silo.cs.indiana.edu:47064/0414/servlet/nameOne

i) I will happily accept any flaws it exhibits at this stage and will try to
fix them: edit, re-compile. Now to access it over the web and work with the new
updated version of the servlet we need to reload the context. 

So we write this servlet:

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class One extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) 
              throws IOException, ServletException {
    HttpSession session = request.getSession();
    String count = (String) session.getAttribute("count");
    if (count == null)
      count = "0"; 
    else  
      count = (Integer.parseInt(count) + 1) + "";
    session.setAttribute("count", count);
    response.setContentType("text/html");  
    PrintWriter out = response.getWriter();
    out.println("<h1>" + count + "</h1>");
  }
}

So next time we will deploy, test and debug this.