An Example Servlet Putting it all together Jan 13 2019 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 webapp 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 import import import javax servlet javax servlet http java io 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 java package 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 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 are 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 directory C 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 with http m174pc4 cis upenn edu 8080 yourLastName index html The End
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