An Example ServletCreditsIt starts with an HTML form...The HTML page, 1The HTML page, 2The deployment descriptorweb.xml 1 -- boilerplateweb.xml 2 -- actual workBeerSelect.java 1BeerSelect.java 2MVCThe model classBeerExpert.javaThe JSP fileresult.jspDirectory structureAccessing the class serverThe EndJan 13, 2019An Example ServletPutting it all togetherCreditsThis is the first example in Head First Servlets & JSP by Brian Basham, Kathy Sierra, and Bert BatesThis is an excellent book, and goes into considerably more detail than we will in this courseIt starts with an HTML form...The HTML page, 1<html> <head> <title>Beer Selection</title> </head> <body> <h1 align="center">Beer Selection Page</h1> ...the form (on the next slide)... </body></html>The HTML page, 2 <form method="POST" action="SelectBeer.do"> Select beer characteristics:<p> Color: <select name="color" size="1"> <option>light</option> <option>amber</option> <option>brown</option> <option>dark</option> </select> <br> <br> <center> <input type="SUBMIT"> </center> </form>The deployment descriptorThe request goes to the server, with the action <form method="POST" action="SelectBeer.do">The name "SelectBeer.do" is not the name of an actual file anywhere; it is a name given to the userPartly, this is for security; you don’t want the user to have access to the actual file without going through your formThe extension .do is just a convention used by this particular book; no extension is necessaryIt is up to the deployment descriptor to find the correct servlet to answer this requestThe deployment descriptor must be named web.xmlweb.xml 1 -- boilerplate<?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/web-app_2_4.xsd" version="2.4"> ...important stuff goes here... </web-app>web.xml 2 -- actual work<servlet> <servlet-name>Ch3 Beer</servlet-name> <servlet-class> com.example.web.BeerSelect </servlet-class></servlet> <servlet-mapping> <servlet-name>Ch3 Beer</servlet-name> <url-pattern>/SelectBeer.do</url-pattern></servlet-mapping>BeerSelect.java 1package com.example.web;import javax.servlet.*;import javax.servlet.http.*;import java.io.*;import java.util.*;import com.example.model.BeerExpert; // notice thispublic class BeerSelect extends HttpServlet { ... doPost method goes here. ..}BeerSelect.java 2 public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { String c = request.getParameter("color"); BeerExpert be = new BeerExpert(); List result = be.getBrands(c); request.setAttribute("styles", result); RequestDispatcher view = request.getRequestDispatcher("result.jsp"); view.forward(request, response); }MVCBeerSelect.java acts as the controllerIt delegates the actual work to a model, BeerExpert.javaIt delegates (forwards) the information to a JSP page that will provide the viewRequestDispatcher view = request.getRequestDispatcher("result.jsp");view.forward(request, response);The model classBeerExpert is the model class; it computes results and adds them to the HttpServletRequest objectNot the HttpServletResponse object; that’s the HTML outputIt returns, in the usual fashion, to the BeerSelect class, which will then forward it to the JSPBeerExpert.javapackage com.example.model;import java.util.*;public class BeerExpert { public List getBrands(String color) { List brands = new ArrayList(); if (color.equals("amber")) { brands.add("Jack Amber"); brands.add("Red Moose"); } else { brands.add("Jail Pale Ale"); brands.add("Gout Stout"); } return brands; }}The JSP fileThe JSP file must have the extension .jspIt is basically HTML, plus a few JSP directivesIt receives the HttpServletRequest and the HttpServletResponse objectsThe HttpServletResponse object may have been partially written by the servlet (but it’s a bad idea)The resultant HTML page goes back to the userresult.jsp<%@ page import="java.util.*" %><html><body><h1 align="center">Beer Recommendations JSP</h1><p><% List styles = (List)request.getAttribute("styles"); Iterator it = styles.iterator(); while (it.hasNext()) { out.print("<br>TRY: " + it.next()); }%></body></html>Directory structure jakarta-tomcat-5.0.12/| webapps/ this is http://m174pc4.cis.upenn.edu:8080/| | beerV1/ | | | form.html| | | result.jsp| | | WEB-INF/| | | | web.xml| | | | classes/| | | | | com/| | | | | | example/| | | | | | | model/| | | | | | | | BeerExpert.class| | | | | | | web/| | | | | | | | BeerSelect.class| | | | lib/| | yourLastName when you ftp, this is where you areAccessing the class serverTomcat should be running 24/7 on m174pc4.cis.upenn.eduTo try it, point your browser to:http://m174pc4.cis.upenn.edu:8080/beerV1/form.htmlWhen you ftp to m174pc4, pwd will tell you that you are in a directory “/”, but you are really in a directoryC:\Tomcat\webapps\yourLastNameThis is the top-level directory for your web applicationsYou should be able to put an HTML file here, say, index.html, and access it withhttp://m174pc4.cis.upenn.edu:8080/yourLastName/index.htmlThe
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