An Example Servlet

1
An Example Servlet

• Putting it all together

2
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

3
It starts with an HTML form...
4
The HTML page, 1
lthtmlgt ltheadgt lttitlegtBeer
Selectionlt/titlegt lt/headgt ltbodygt lth1
align"center"gtBeer Selection Pagelt/h1gt
...the form (on the next slide)...
lt/bodygt lt/htmlgt
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The HTML page, 2
ltform method"POST" action"SelectBeer.do"gt
Select beer characteristicsltpgt Color
ltselect name"color" size"1"gt
ltoptiongtlightlt/optiongt ltoptiongtamberlt/opti
ongt ltoptiongtbrownlt/optiongt
ltoptiongtdarklt/optiongt lt/selectgt ltbrgt
ltbrgt ltcentergt ltinput
type"SUBMIT"gt lt/centergt lt/formgt
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The deployment descriptor

• The request goes to the server, with the action
  ltform method"POST" action"SelectBeer.do"gt
• 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 dont 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

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web.xml 1 -- boilerplate
lt?xml version"1.0" encoding"ISO-8859-1"?gt ltweb-
app xmlns"http//java.sun.com/xml/ns/j2ee"
xmlnsxsi"http//www.w3.org/2001/XMLSchema-ins
tance" xsischemaLocation"http//java.su
n.com/xml/ns/j2ee/web-app_2_4.xsd"
version"2.4"gt ...important stuff goes
here... lt/web-appgt
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web.xml 2 -- actual work
ltservletgt ltservlet-namegtCh3
Beerlt/servlet-namegt ltservlet-classgt
com.example.web.BeerSelect lt/servlet-classgt lt/
servletgt ltservlet-mappinggt
ltservlet-namegtCh3 Beerlt/servlet-namegt
lturl-patterngt/SelectBeer.dolt/url-patterngt lt/servle
t-mappinggt
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BeerSelect.java 1
package com.example.web import
javax.servlet. import javax.servlet.http. impo
rt java.io. import java.util. import
com.example.model.BeerExpert // notice
this public class BeerSelect extends HttpServlet
... doPost method goes here. ..
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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)
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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.f
  orward(request, response)

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The model class

• BeerExpert is the model class it computes
  results and adds them to the HttpServletRequest
  object
• Not the HttpServletResponse object thats the
  HTML output
• It returns, in the usual fashion, to the
  BeerSelect class, which will then forward it to
  the JSP

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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
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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 its a bad
  idea)
• The resultant HTML page goes back to the user

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result.jsp
lt_at_ page import"java.util." gt lthtmlgt ltbodygt lth
1 align"center"gtBeer Recommendations
JSPlt/h1gt ltpgt lt List styles
(List)request.getAttribute("styles") Iterator
it styles.iterator() while (it.hasNext())
out.print("ltbrgtTRY " it.next())
gt lt/bodygt lt/htmlgt
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Directory structure
jakarta-tomcat-5.0.12/ webapps/ ? this is
http//m174pc4.cis.upenn.edu8080/
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
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Accessing the class server

• Tomcat should be running 24/7 on
  m174pc4.cis.upenn.edu
• To try it, point your browser tohttp//m174pc4.c
  is.upenn.edu8080/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.edu8080/yourLastName/index.html

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The End