Servlets

1
Servlets

• N.L. Hsueh
• 2003/9

2
Outline
3
Introduction

• Java networking capabilities
• Socket-based and packet-based communications
• Package java.net
• Remote Method Invocation (RMI)
• Package java.rmi
• Servlets and Java Server Pages (JSP)
• Request-response model
• Packages javax.servlet, javax.servlet.http,
  javax.servlet.jsp, javax.servlet.tagext
• Form the Web tier of J2EE

4
Conti.

• Servlets
• A Java program running in the context of a web
  server that can respond to many clients and
  communicate with other servers
• Server-side (as opposed to Java applet)
• Request/response mechanism
• Alternative for CGI, NSAPI, ISAPI, etc
• Support thin clients
• Session-tracking capabilities

5
Servlets in Multi-Tier Systems

• Servlet is in middle of three-tier system
• Web page client, communicates using HTTP with
• Web server, which can run Java servlet, which in
  turn communicates through JDBC with
• Database Server (e.g. Oracle)
• Servlet provide all the services of standard CGI
• Servlet API is a standard extension to the JDK
  under javax
• Package javax.servlet, Package javax.servlet.http

6
Servlets vs. CGI
Gateway Programs
HTTP request
Run CGI Script or CGI Program (Process)
CGI
HTTP response
Output
Web Server
7
Conti.
8
Conti.

• Tomcat
• Jakarta project
• Official reference implementation of the JSP and
  servlet standards

9
Architecture
Model 1
10
Conti.
Model 2
11
Conti.

• Benefits of Model 2
• Using MVC architecture
• Servlets do not deal with presentation logic at
  all but rather just process HTTP requests and
  control the flow of the application.
• The model implementing the business logic sends
  objects or JavaBeans to the view, therefore
  encouraging a much cleaner separation of business
  and presentation logic and making application
  development and maintenance much easier

12
Servlet Container

• Servlet container (servlet engine)
• Server that executes a servlet
• Web servers and application servers
• Netscape iPlanet Application Server
• Microsofts Internet Information Server (IIS)
• Apache HTTP Server
• BEAs WebLogic Application Server
• IBMs WebSphere Application Server
• World Wide Web Consortiums Jigsaw Web Server

13
Working Process

• A client sends an HTTP request to the server or
  servlet container
• The server or servlet container receives the
  request and directs it the be processed by the
  appropriate servlet
• The servlet does its processing, which may
  include interacting with a database or other
  server-side components such as other servlets,
  JSP or enterprise java bean
• The servlet returns its result to the client in
  the form of html, xhtml or xml document

14
UML Presentation
15
Servlet Life Cycle

• void init (ServletConfig config) called once at
  start
• ServletConfig getServletConfig() access to
  servlet information
• String getServletInfo() useful for allowing use
  to get servlet information
• void service (ServletRequest req, ServletResponse
  resp) called as often as needed to respond to
  requests
• void destroy() called once for cleanup when
  stopped

16
Interface Servlet

• Interface Servlet
• All servlets must implement this interface
• All methods of interface Servlet are invoked
  automatically
• Default implementation of Servlet
• Abstract class GenericServlet
• Abstract class HttpServlet

17
Servlet.init()

• public void init (ServletConfig config)
• Be invoked when the servlet is first started.
• Be called only once
• ServletConfig object passed as the parameter has
  a method getServletContext ( )
• returns a ServletContext with information about
  the servlet environment

18
Servlet Initialization Information

• This information is passed to the servlet via the
  ServletConfig object parameter of the init
  method.
• Each web server has its own information tags
  defined.
• The getInitParameterNames ( ) returns an
  Enumeration of all the parameters available to
  the servlet on that server.
• A particular parameter is obtained by
• config.getInitParameter ( timezone)

19
Servlet Context Information

• This information is available through the
  ServerConfig object.
• save the ServerConfig parameter from the init
  method.
• ServletContext c config.getServletContext ( )
• The ServletContext object has methods
• getAttribute
• getMimeType
• getRealPath
• getServerInfo
• getServlet (String name )
• getServletNames
• log (String message )

20

• public void init(ServletConfig c) throws
  ServletException
• dbUser c.getServletConfig().getInitParameter(
  "dbUser" )
• driver c.getServletConfig().getInitParameter(
  "driver" )
• dbUrl c.getServletConfig().getInitParameter(
  "dbUrl" )
• Msg c.getServletConfig().getInitParameter(
  "exampleMsg" )

An example of ServletContext
21
Servlet.service()

• public void service (ServletRequest req,
  ServletResponse res)
• Each request message from the client results in
  invoking the service method.
• Two ways the client can send information
• parameter name/value pairs
• streams - the servlet can invoke
  getInputStream(), which returns a
  ServletInputStream.
• Servlet can invoke getOutputStream() to generate
  the response.
• More than one instance of the service method can
  be invoked at one time to respond to multiple
  requests.

22
Servlet.destroy()

• Called when the servlet in unloaded to clean up
  any open resources.
• Server normally waits until all service calls are
  terminated to invoke destroy
• The destroy method should make sure that
  resources are not being used.

23
HttpServlet Class

• Overrides method service
• Two most common HTTP request types
• get requests
• post requests
• Method doGet responds to get requests
• Method doPost responds to post requests
• HttpServletRequest and HttpServletResponse objects

24

• HttpServletRequest interface
• Web server creates an HttpServletRequest object
  and passes it to the servlets service method
• HttpServletRequest object contains the request
  from the client
• HttpServletResponse interface
• Web server creates an HttpServletResponse object
  and passes it to the servlets service method
• HttpServletResponse object contains the response
  to the client

25
UML Presentation
26
Handling HTTP get Requests

• get request
• Retrieve the content of a URL
• Example WelcomeServlet
• a servlet handles HTTP get requests

27
// WelcomeServlet.java // A simple servlet to
process get requests. import javax.servlet. imp
ort javax.servlet.http. import
java.io. public class WelcomeServlet extends
HttpServlet // process "get" requests
from clients protected void doGet(
HttpServletRequest request,
HttpServletResponse response ) throws
ServletException, IOException
response.setContentType( "text/html" )
PrintWriter out response.getWriter()
// send XHTML page to client // start
XHTML document out.println( "lt?xml version
\"1.0\"?gt" ) out.println( "lt!DOCTYPE
html PUBLIC \"-//W3C//DTD " "XHTML 1.0
Strict//EN\" \"http//www.w3.org"
"/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt" )
28
out.println( "lthtml xmlns
\"http//www.w3.org/1999/xhtml\"gt" )
// head section of document out.println(
"ltheadgt" ) out.println( "lttitlegtA Simple
Servlet Examplelt/titlegt" ) out.println(
"lt/headgt" ) // body section of
document out.println( "ltbodygt" )
out.println( "lth1gtWelcome to Servlets!lt/h1gt" )
out.println( "lt/bodygt" ) // end
XHTML document out.println( "lt/htmlgt" )
out.close() // close stream to complete the
page
29
(No Transcript)
30
Compiling Servlets

• Software requirement
• j2sdk1.4.1, j2sdkee1.3.1
• JAVA_HOME
• For example, c\j2sdk1.4.1
• J2EE_HOME
• For example, c\j2sdkee1.3.1
• CLASSPATH
• JAVA_HOME\lib\.jar J2EE_HOME\lib\.jar

31
Setting Up Tomcat Server

• Download Tomcat (version 3.2.3)
• Jakarta.apache.org/builds/jakarta-tomcat/release/v
  3.2.3/bin/
• Define environment variables
• JAVA_HOME
• TOMCAT_HOME
• Start the Tomcat server
• tomcat start
• Launch the Tomcat server
• http//localhost8080/

32
Conti.
33
Deploying Web Applications

• Web applications
• JSPs, servlets and their supporting files
• Deploying a Web application
• Directory structure
• Context root
• Web application archive file (WAR file)
• Deployment descriptor
• web.xml

34
lt!DOCTYPE web-app PUBLIC "-//Sun Microsystems,
Inc.//DTD Web Application 2.2//EN"
"http//java.sun.com/j2ee/dtds/web-app_2_2.dtd"gt
ltweb-appgt lt!-- General description of your Web
application --gt ltdisplay-namegt First
Servlet Example Demo lt/display-namegt
ltdescriptiongt This is the Web application
in which we demonstrate our Servlet example
lt/descriptiongt lt!-- Servlet definitions --gt
ltservletgt ltservlet-namegtwelcomelt/servlet-na
megt ltdescriptiongt A servlet that
returns a "Welcome" screen through an HTTP get
request lt/descriptiongt
ltservlet-classgt neo.WelcomeServlet
lt/servlet-classgt lt/servletgt
web.xml
35
lt!-- Servlet mappings --gt ltservlet-mappinggt
ltservlet-namegtwelcomelt/servlet-namegt
lturl-patterngt/welcomelt/url-patterngt
lt/servlet-mappinggt lt!-- Neo --gt lt/web-appgt
web.xml (conti.)
36
Cont.
37
Handling HTTP get Requests Containing Data

• Servlet WelcomeServlet2
• Responds to a get request that contains data

38
WelcomeServlet2.java
39
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40
9.5 Handling HTTP post Requests

• HTTP post request
• Post data from an HTML form to a server-side form
  handler
• Browsers cache Web pages
• Servlet WelcomeServlet3
• Responds to a post request that contains data

41
WelcomeServlet3.java
42
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43
9.6 Redirecting Requests to Other Resources

• Servlet RedirectServlet
• Redirects the request to a different resource

44
RedirectServlet.java
45
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46
9.7 Session Tracking

• Personalization
• Privacy invasion
• HTTP stateless protocol
• Does not support persistent information
• Track clients individually
• Cookies
• Session tracking
• hidden type input
• URL rewriting

47
9.7.1 Cookies

• Stored on the users computer for retrieval later
• Text-based data sent by servlets
• Maximum age of a cookie
• Deleted automatically when they expire
• Servlet CookieServlet
• Handles both get and post requests

48
Fig. 9.20 Storing user data on the client
computer with cookies.Lines 14-20Line
28Line 29 Line 30Line 32

• 1 // Fig. 9.20 CookieServlet.java
• 2 // Using cookies to store data on the client
  computer.
• 3 package com.deitel.advjhtp1.servlets
• 4
• 5 import javax.servlet.
• 6 import javax.servlet.http.
• 7 import java.io.
• 8 import java.util.
• 9
• 10 public class CookieServlet extends
  HttpServlet
• 11 private final Map books new HashMap()
• 12
• 13 // initialize Map books
• 14 public void init()
• 15
• 16 books.put( "C", "0130895725" )
• 17 books.put( "C", "0130895717" )
• 18 books.put( "Java", "0130125075" )
• 19 books.put( "VB6", "0134569555" )

49
Fig. 9.20 Storing user data on the client
computer with cookies.

• 36 // send XHTML page to client
• 37
• 38 // start XHTML document
• 39 out.println( "lt?xml version
  \"1.0\"?gt" )
• 40
• 41 out.println( "lt!DOCTYPE html PUBLIC
  \"-//W3C//DTD "
• 42 "XHTML 1.0 Strict//EN\"
  \"http//www.w3.org"
• 43 "/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt
  " )
• 44
• 45 out.println(
• 46 "lthtml xmlns \"http//www.w3.org/1
  999/xhtml\"gt" )
• 47
• 48 // head section of document
• 49 out.println( "ltheadgt" )
• 50 out.println( "lttitlegtWelcome to
  Cookieslt/titlegt" )
• 51 out.println( "lt/headgt" )
• 52
• 53 // body section of document
• 54 out.println( "ltbodygt" )

50
Fig. 9.20 Storing user data on the client
computer with cookies.Line 77

• 71 // read cookies from client and create
  XHTML document
• 72 // containing recommended books
• 73 protected void doGet( HttpServletRequest
  request,
• 74 HttpServletResponse response )
• 75 throws ServletException,
  IOException
• 76
• 77 Cookie cookies request.getCookies()
  // get cookies
• 78
• 79 response.setContentType( "text/html"
  )
• 80 PrintWriter out response.getWriter()
  
• 81
• 82 // start XHTML document
• 83 out.println( "lt?xml version
  \"1.0\"?gt" )
• 84
• 85 out.println( "lt!DOCTYPE html PUBLIC
  \"-//W3C//DTD "
• 86 "XHTML 1.0 Strict//EN\"
  \"http//www.w3.org"
• 87 "/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt
  " )
• 88
• 89 out.println(

51
Fig. 9.20 Storing user data on the client
computer with cookies.

• 105 // get the name of each cookie
• 106 for ( int i 0 i lt
  cookies.length i )
• 107 out.println( cookies i
  .getName()
• 108 " How to Program. ISBN "
• 109 cookies i .getValue()
  "ltbr /gt" )
• 110
• 111 out.println( "lt/pgt" )
• 112
• 113 else // there were no cookies
• 114 out.println( "lth1gtNo
  Recommendationslt/h1gt" )
• 115 out.println( "ltpgtYou did not select
  a language.lt/pgt" )
• 116
• 117
• 118 out.println( "lt/bodygt" )
• 119
• 120 // end XHTML document
• 121 out.println( "lt/htmlgt" )
• 122 out.close() // close stream
• 123

52
Fig. 9.21 CookieSelectLanguage.html document for
selecting a programming language and posting the
data to the CookieServlet.

• 1 lt?xml version "1.0"?gt
• 2 lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN"
• 3 "http//www.w3.org/TR/xhtml1/DTD/xhtml1-st
  rict.dtd"gt
• 4
• 5 lt!-- Fig. 9.21 CookieSelectLanguage.html
  --gt
• 6
• 7 lthtml xmlns "http//www.w3.org/1999/xhtml"gt
  
• 8 ltheadgt
• 9 lttitlegtUsing Cookieslt/titlegt
• 10 lt/headgt
• 11
• 12 ltbodygt
• 13 ltform action "/advjhtp1/cookies" method
  "post"gt
• 14
• 15 ltpgtSelect a programming languagelt/pgt
• 16 ltpgt
• 17 ltinput type "radio" name
  "language"
• 18 value "C" /gtC ltbr /gt
• 19

53
Fig. 9.21 CookieSelectLanguage.html document for
selecting a programming language and posting the
data to the CookieServlet. Program output
54
Fig. 9.21 CookieSelectLanguage.html document for
selecting a programming language and posting the
data to the CookieServlet. Program output
55
9.7.1 Cookies (Cont.)
56
9.7.1 Cookies (Cont.)
Fig. 9.23 (Part 1 of 2) Important methods of
class Cookie.
57
9.7.1 Cookies (Cont.)
58
9.7.2 Session Tracking with HttpSession

• Interface HttpSession
• Supports session tracking
• Servlet SessionServlet
• Uses HttpSession objects
• Handles both get and post requests

59
Fig. 9.24 Maintaining state information with
HttpSession objects.Line 28Line 32Line 35

• 1 // Fig. 9.24 SessionServlet.java
• 2 // Using HttpSession to maintain client
  state information.
• 3 package com.deitel.advjhtp1.servlets
• 4
• 5 import javax.servlet.
• 6 import javax.servlet.http.
• 7 import java.io.
• 8 import java.util.
• 9
• 10 public class SessionServlet extends
  HttpServlet
• 11 private final Map books new HashMap()
• 12
• 13 // initialize Map books
• 14 public void init()
• 15
• 16 books.put( "C", "0130895725" )
• 17 books.put( "C", "0130895717" )
• 18 books.put( "Java", "0130125075" )
• 19 books.put( "VB6", "0134569555" )

60
Fig. 9.24 Maintaining state information with
HttpSession objects.Line 64Line 67

• 36
• 37 response.setContentType( "text/html"
  )
• 38 PrintWriter out response.getWriter()
  
• 39
• 40 // send XHTML page to client
• 41
• 42 // start XHTML document
• 43 out.println( "lt?xml version
  \"1.0\"?gt" )
• 44
• 45 out.println( "lt!DOCTYPE html PUBLIC
  \"-//W3C//DTD "
• 46 "XHTML 1.0 Strict//EN\"
  \"http//www.w3.org"
• 47 "/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt
  " )
• 48
• 49 out.println(
• 50 "lthtml xmlns \"http//www.w3.org/1
  999/xhtml\"gt" )
• 51
• 52 // head section of document
• 53 out.println( "ltheadgt" )
• 54 out.println( "lttitlegtWelcome to
  Sessionslt/titlegt" )

61
Fig. 9.24 Maintaining state information with
HttpSession objects.Line 71Line 74Line
77Line 100

• 70 out.println( "The session was created
  at "
• 71 new Date( session.getCreationTime()
  ) "ltbr /gt" )
• 72
• 73 out.println( "You last accessed the
  session at "
• 74 new Date( session.getLastAccessedTim
  e() ) "ltbr /gt" )
• 75
• 76 out.println( "The maximum inactive
  interval is "
• 77 session.getMaxInactiveInterval()
  " secondslt/pgt" )
• 78
• 79 out.println( "ltpgtlta href "
• 80 "\"servlets/SessionSelectLanguage.ht
  ml\"gt"
• 81 "Click here to choose another
  languagelt/agtlt/pgt" )
• 82
• 83 out.println( "ltpgtlta href
  \"sessions\"gt"
• 84 "Click here to get book
  recommendationslt/agtlt/pgt" )
• 85 out.println( "lt/bodygt" )
• 86
• 87 // end XHTML document
• 88 out.println( "lt/htmlgt" )

62
Fig. 9.24 Maintaining state information with
HttpSession objects.Line 106

• 105 if ( session ! null )
• 106 valueNames session.getAttributeNam
  es()
• 107 else
• 108 valueNames null
• 109
• 110 PrintWriter out response.getWriter()
  
• 111 response.setContentType( "text/html"
  )
• 112
• 113 // start XHTML document
• 114 out.println( "lt?xml version
  \"1.0\"?gt" )
• 115
• 116 out.println( "lt!DOCTYPE html PUBLIC
  \"-//W3C//DTD "
• 117 "XHTML 1.0 Strict//EN\"
  \"http//www.w3.org"
• 118 "/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt
  " )
• 119
• 120 out.println(
• 121 "lthtml xmlns \"http//www.w3.org/1
  999/xhtml\"gt" )
• 122
• 123 // head section of document

63
Fig. 9.24 Maintaining state information with
HttpSession objects.Line 141

• 138 // get value for each name in
  valueNames
• 139 while ( valueNames.hasMoreElements()
  )
• 140 name valueNames.nextElement().t
  oString()
• 141 value session.getAttribute(
  name ).toString()
• 142
• 143 out.println( name " How to
  Program. "
• 144 "ISBN " value "ltbr /gt"
  )
• 145
• 146
• 147 out.println( "lt/pgt" )
• 148
• 149 else
• 150 out.println( "lth1gtNo
  Recommendationslt/h1gt" )
• 151 out.println( "ltpgtYou did not select
  a language.lt/pgt" )
• 152
• 153
• 154 out.println( "lt/bodygt" )
• 155
• 156 // end XHTML document

64
Fig. 9.25 SessionSelectLanguage.html document for
selecting a programming language and posting the
data to the SessionServlet.

• 1 lt?xml version "1.0"?gt
• 2 lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN"
• 3 "http//www.w3.org/TR/xhtml1/DTD/xhtml1-st
  rict.dtd"gt
• 4
• 5 lt!-- Fig. 9.25 SessionSelectLanguage.html
  --gt
• 6
• 7 lthtml xmlns "http//www.w3.org/1999/xhtml"gt
  
• 8 ltheadgt
• 9 lttitlegtUsing Sessionslt/titlegt
• 10 lt/headgt
• 11
• 12 ltbodygt
• 13 ltform action "/advjhtp1/sessions"
  method "post"gt
• 14
• 15 ltpgtSelect a programming languagelt/pgt
• 16 ltpgt
• 17 ltinput type "radio" name
  "language"
• 18 value "C" /gtC ltbr /gt
• 19

65
Fig. 9.25 SessionSelectLanguage.html document for
selecting a programming language and posting the
data to the SessionServlet.Program output
66
Fig. 9.25 SessionSelectLanguage.html document for
selecting a programming language and posting the
data to the SessionServlet. Program output
67
Fig. 9.25 SessionSelectLanguage.html document for
selecting a programming language and posting the
data to the SessionServlet. Program output
68
Fig. 9.25 SessionSelectLanguage.html document for
selecting a programming language and posting the
data to the SessionServlet. Program output
69
9.7.2 Session Tracking with HttpSession (Cont.)
70
9.8 Multi-Tier Applications Using JDBC from a
Servlet

• Three-tier distributed applications
• User interface
• Business logic
• Database access
• Web servers often represent the middle tier
• Three-tier distributed application example
• SurveyServlet
• Survey.html
• Cloudscape database

71
Fig. 9.27 Multi-tier Web-based survey using
XHTML, servlets and JDBC.Lines 16-54Line
21Lines 22-23Lines 27-31

• 1 // Fig. 9.27 SurveyServlet.java
• 2 // A Web-based survey that uses JDBC from a
  servlet.
• 3 package com.deitel.advjhtp1.servlets
• 4
• 5 import java.io.
• 6 import java.text.
• 7 import java.sql.
• 8 import javax.servlet.
• 9 import javax.servlet.http.
• 10
• 11 public class SurveyServlet extends
  HttpServlet
• 12 private Connection connection
• 13 private PreparedStatement updateVotes,
  totalVotes, results
• 14
• 15 // set up database connection and prepare
  SQL statements
• 16 public void init( ServletConfig config )
• 17 throws ServletException
• 18
• 19 // attempt database connection and
  create PreparedStatements

72
Fig. 9.27 Multi-tier Web-based survey using
XHTML, servlets and JDBC.Lines 34-44

• 33 // PreparedStatement to sum the
  votes
• 34 totalVotes
• 35 connection.prepareStatement(
• 36 "SELECT sum( votes ) FROM
  surveyresults"
• 37 )
• 38
• 39 // PreparedStatement to obtain
  surveyoption table's data
• 40 results
• 41 connection.prepareStatement(
• 42 "SELECT surveyoption, votes,
  id "
• 43 "FROM surveyresults ORDER BY
  id"
• 44 )
• 45
• 46
• 47 // for any exception throw an
  UnavailableException to
• 48 // indicate that the servlet is not
  currently available
• 49 catch ( Exception exception )
• 50 exception.printStackTrace()
• 51 throw new UnavailableException(excep
  tion.getMessage())

73
Fig. 9.27 Multi-tier Web-based survey using
XHTML, servlets and JDBC.Lines 80-81Lines
87-88Lines 91-93Lines 96-123

• 66 // start XHTML document
• 67 out.println( "lt?xml version
  \"1.0\"?gt" )
• 68
• 69 out.println( "lt!DOCTYPE html PUBLIC
  \"-//W3C//DTD "
• 70 "XHTML 1.0 Strict//EN\"
  \"http//www.w3.org"
• 71 "/TR/xhtml1/DTD/xhtml1-strict.dtd\"gt
  " )
• 72
• 73 out.println(
• 74 "lthtml xmlns \"http//www.w3.org/1
  999/xhtml\"gt" )
• 75
• 76 // head section of document
• 77 out.println( "ltheadgt" )
• 78
• 79 // read current survey response
• 80 int value
• 81 Integer.parseInt(
  request.getParameter( "animal" ) )
• 82
• 83 // attempt to process a vote and
  display current results
• 84 try

74
Fig. 9.27 Multi-tier Web-based survey using
XHTML, servlets and JDBC.

• 100 out.println( "ltbodygt" )
• 101 out.println( "ltpgtThank you for
  participating." )
• 102 out.println( "ltbr
  /gtResultslt/pgtltpregt" )
• 103
• 104 // process results
• 105 int votes
• 106
• 107 while ( resultsRS.next() )
• 108 out.print( resultsRS.getString(
  1 ) )
• 109 out.print( " " )
• 110 votes resultsRS.getInt( 2 )
• 111 out.print( twoDigits.format(
• 112 ( double ) votes / total
  100 ) )
• 113 out.print( " responses " )
• 114 out.println( votes )
• 115
• 116
• 117 resultsRS.close()
• 118

75
Fig. 9.27 Multi-tier Web-based survey using
XHTML, servlets and JDBC.Lines 140-154

• 135
• 136
• 137 // end of doPost method
• 138
• 139 // close SQL statements and database when
  servlet terminates
• 140 public void destroy()
• 141
• 142 // attempt to close statements and
  database connection
• 143 try
• 144 updateVotes.close()
• 145 totalVotes.close()
• 146 results.close()
• 147 connection.close()
• 148
• 149
• 150 // handle database exceptions by
  returning error to client
• 151 catch( SQLException sqlException )
• 152 sqlException.printStackTrace()
• 153

76
Fig. 9.28 Survey.html document that allows users
to submit survey responses to SurveyServlet.

• 1 lt?xml version "1.0"?gt
• 2 lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN"
• 3 "http//www.w3.org/TR/xhtml1/DTD/xhtml1-st
  rict.dtd"gt
• 4
• 5 lt!-- Fig. 9.28 Survey.html --gt
• 6
• 7 lthtml xmlns "http//www.w3.org/1999/xhtml"gt
  
• 8 ltheadgt
• 9 lttitlegtSurveylt/titlegt
• 10 lt/headgt
• 11
• 12 ltbodygt
• 13 ltform method "post" action
  "/advjhtp1/animalsurvey"gt
• 14
• 15 ltpgtWhat is your favorite pet?lt/pgt
• 16
• 17 ltpgt
• 18 ltinput type "radio" name "animal"
• 19 value "1" /gtDogltbr /gt

77
Fig. 9.28 Survey.html document that allows users
to submit survey responses to SurveyServlet.
78
9.8 Multi-Tier Applications Using JDBC from a
Servlet (Cont.)
79
9.9 HttpUtils Class