Servlet Tutorial Power Point

Apr 11, 2023

An Example Servlet

Putting it all together

Credits

This is the first example in Head First Servlets & JSP by Brian Basham, Kathy Sierra, and Bert Bates

This is an excellent book, and goes into considerably more detail than we will in this course

It 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 descriptor

The 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 user Partly, this is for security; you don’t want the user to have

access to the actual file without going through your form The extension .do is just a convention used by this

particular book; no extension is necessary It is up to the deployment descriptor to find the

correct servlet to answer this request The deployment descriptor must be named web.xml

web.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 1

package com.example.web;

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

import com.example.model.BeerExpert; // notice this

public 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); }

MVC

BeerSelect.java acts as the controller It delegates the actual work to a model,

BeerExpert.java It delegates (forwards) the information to a JSP page

that will provide the view RequestDispatcher view =

request.getRequestDispatcher("result.jsp");view.forward(request, response);

The model class

BeerExpert is the model class; it computes results and adds them to the HttpServletRequest object Not the HttpServletResponse object; that’s the HTML

output It returns, in the usual fashion, to the BeerSelect

class, which will then forward it to the JSP

BeerExpert.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 file

The JSP file must have the extension .jsp It is basically HTML, plus a few JSP directives It receives the HttpServletRequest and the

HttpServletResponse objects The HttpServletResponse object may have been

partially written by the servlet (but it’s a bad idea) The resultant HTML page goes back to the user

result.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>

Accessing the class server

Tomcat should be running 24/7 on m174pc4.cis.upenn.edu To try it, point your browser to:

http://m174pc4.cis.upenn.edu:8080/beerV1/form.html

When you ftp to m174pc4, pwd will tell you that you are in a directory “/”, but you are really in a directoryC:\Tomcat\webapps\yourLastName

This is the top-level directory for your web applications You should be able to put an HTML file here, say, index.html,

and access it withhttp://m174pc4.cis.upenn.edu:8080/yourLastName/index.html

The End

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