Metodo não me retorna a Array, porque?

Front-end
#1

Estou estudando Servlets e JSP pelo livro Use a Cabeça
e quando eu executo , ele abre o html, quando eu seleciono o tamanhoe clico no botão, ele não me retorna nada, porque???

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Testando Array</title>
</head>
<body>
<h1 align="center">Seleciona a quantidade</h1>
<form method="POST" action="SelectTamanho.do">
Selecione o Tamanho
<input type=checkbox name=sizes value="12oz">12 oz.<br>
<input type=checkbox name=sizes value="16oz">16 oz.<br>

<center><input type="SUBMIT"></center>
</form>
</body>
</html>
package com.example.web;

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

public class TamanhoSelect extends HttpServlet{
	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
		//String one = request.getParameterValues("sizes")[0];
		String [] sizes = request.getParameterValues("sizes");
		PrintWriter out = response.getWriter();
		for (int x=0; x < sizes.length; x++)
		{
			out.println("<br>sizes: " + sizes[x]);
		}
	}

}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <servlet>
    <servlet-name>Ch4 Beer</servlet-name>
    <servlet-class>com.example.web.TamanhoSelect</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Ch4 Beer</servlet-name>
    <url-pattern>/SelectTamanho.do</url-pattern>
  </servlet-mapping>
</web-app>
#2

o valor de name e type do seu input deveria estar entre aspas, fora isso não vi mais nada de estranho.

e a classe HttpServlet tem o método doPost protected e não public

#3