5.1 servlets n http request

7/30/2019 5.1 Servlets n Http Request

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2004 Prentice Hall, Inc. All rights reserved.

Chapter 36 - Servlets:

Bonus for Java DevelopersOutline

36.1 Introduction36.2 Servlet Overview and Architecture

36.2.1 Interface Servlet and the Servlet Life Cycle36.2.2 HttpServlet Class36.2.3 HttpServletRequest Interface36.2.4 HttpServletResponse Interface

36.3 Handling HTTP get Requests36.3.1 Setting Up the Apache Tomcat Server

36.3.2 Deploying a Web Application

36.4 Handling HTTP get Requests Containing Data36.5 Handling HTTP post Requests36.6 Redirecting Requests to Other Resources

36.7 Multi-Tier Applications: Using JDBC from a Servlet

36.8 Web Resources


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Objectives

In this lesson, you will learn: To execute servlets with the Apache Tomcat server.

To be able to respond to HTTP requests from an

HttpServlet.

To be able to redirect requests to static and dynamic Webresources.


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36.1 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


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36.1 Introduction (Cont.)

Servlets Thin clients

Request/response mechanism

redirection

Tomcat Jakarta project

Official reference implementation of the JSP and servlet

standards


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36.2 Servlet Overview and Architecture

Servlet container (servlet engine) Server that executes a servlet

Web servers and application servers Sun ONE 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


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36.2.1 Interface Servlet and the Servlet LifeCycle

Interface Servlet All servlets must implement this interface

All methods of interface Servlet are invoked by servlet

container

Servlet life cycle Servlet container invokes the servlets init method

Servlets service method handles requests

Servlets destroy method releases servlet resources when

the servlet container terminates the servlet Servlet implementation

GenericServlet

HttpServlet


7/57 2004 Prentice Hall, Inc. All rights reserved.

36.2.1 Interface Servlet and the Servlet LifeCycle (Cont.)

Method Descriptionvoid init(ServletConfigconfig )

The servlet container calls this method once during a servlets execution cycle to initialize theservlet. The ServletConfig argument is supplied by the servlet container that executes theservlet.

ServletConfiggetServletConfig()

This method returns a reference to an object that implements interface ServletConfig. This

object provides access to the servlets configuration information such as servlet initializationparameters and the servlets ServletContext, which provides the servlet with access to itsenvironment (i.e., the servlet container in which the servlet executes).

StringgetServletInfo()

This method is defined by a servlet programmer to return a string containing servlet informationsuch as the servlets author and version.

void service(ServletRequestrequest,ServletResponseresponse )

The servlet container calls this method to respond to a client request to the servlet.

void destroy()This cleanup method is called when a servlet is terminated by its servlet container. Resources

used by the servlet, such as an open file or an open database connection, should be deallocated here.

Fig. 36.1 Methods of interface Servlet (package javax.servlet).



36.2.2 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



36.2.2 HttpServlet Class (Cont.)

Method DescriptiondoDelete Called in response to an HTTP delete request. Such a request is normally used

to delete a file from a server. This may not be available on some servers, becauseof its inherent security risks (e.g., the client could delete a file that is critical tothe execution of the server or an application).

doHead Called in response to an HTTP headrequest. Such a request is normally usedwhen the client only wants the headers of a response, such as the content type andcontent length of the response.

doOptions Called in response to an HTTP options request. This returns information to theclient indicating the HTTP options supported by the server, such as the version ofHTTP (1.0 or 1.1) and the request methods the server supports.

doPut Called in response to an HTTPput request. Such a request is normally used tostore a file on the server. This may not be available on some servers, because ofits inherent security risks (e.g., the client could place an executable application onthe server, which, if executed, could damage the serverperhaps by deletingcritical files or occupying resources).

doTrace Called in response to an HTTP trace request. Such a request is normally usedfor debugging. The implementation of this method automatically returns anHTML document to the client containing the request header information (datasent by the browser as part of the request).

Fig.36.2 Other methods of class HttpServlet.



36.2.3 HttpServletRequest Interface

Web server creates an HttpServletRequest object

passes it to the servlets service method

HttpServletRequest object contains the request

from the client



36.2.3 HttpServletRequest Interface(Cont.)

Method DescriptionStringgetParameter(String name )

Obtains the value of a parameter sent to the servlet as part of a get orpost request. Thename argument represents the parameter name.

EnumerationgetParameterNames()

Returns the names of all the parameters sent to the servlet as part of a post request.

String[]getParameterValues( String name )

For a parameter with multiple values, this method returns an array of strings containing thevalues for a specified servlet parameter.

Cookie[]getCookies()

Returns an array ofCookie objects stored on the client by the server. Cookie objects canbe used to uniquely identify clients to the servlet.

HttpSessiongetSession(boolean create )

Returns an HttpSession object associated with the clients current browsing session.This method can create an HttpSession object (true argument) if one does not alreadyexist for the client. HttpSession objects are used in similar ways to Cookies foruniquely identifying clients.

Fig. 36.3 Some methods of interface HttpServletRequest.



36.2.4 HttpServletResponse Interface

Web server creates an HttpServletResponse object

passes it to the servlets service method



36.2.4 HttpServletResponse Interface(Cont.)

Method Descriptionvoid addCookie(Cookie cookie )

Used to add a Cookie to the header of the response to the client. The

Cookies maximum age and whetherCookies are enabled on the clientdetermine ifCookies are stored on the client.

ServletOutputStreamgetOutputStream()

Obtains a byte-based output stream for sending binary data to the client.

PrintWritergetWriter()

Obtains a character-based output stream for sending text data to the client.

voidsetContentType(String type )

Specifies the MIME type of the response to the browser. The MIME type

helps the browser determine how to display the data (or possibly what

other application to execute to process the data). For example, MIME type

"text/html" indicates that the response is an HTML document, so thebrowser displays the HTML page.

Fig. 36.4 Some methods of interface HttpServletResponse.



36.3 Handling HTTP get Requests

get request Retrieve the content of a URL

Example: WelcomeServlet a servlet handles HTTP get requests

1 // Fig 36 5: WelcomeServlet java


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2004 Prentice Hall, Inc.

All rights reserved.

Outline

1 // Fig. 36.5: WelcomeServlet.java

2 // A simple servlet to process get requests.

3

4 import javax.servlet.*;

5 import javax.servlet.http.*;

6 import java.io.*;

7

8 publicclass WelcomeServlet extends HttpServlet {

9

10 // process "get" requests from clients

11 protectedvoid doGet( HttpServletRequest request,

12 HttpServletResponse response )

13 throws ServletException, IOException

14{

15 response.setContentType( "text/html" );

16 PrintWriter out = response.getWriter();

17

18 // send XHTML page to client

19

20 // start XHTML document

21 out.println( "" );22

23 out.println( "" );

WelcomeServlet.java

(1 of 2)

Import the javax.servlet andjavax.servlet.http packages.

Extends HttpServlet tohandle HTTP get requestsand HTTP post requests.

Override method doGet toprovide custom get request

processing.

Uses the response objectssetContentType method tospecify the content type of the data to

be sent as the response to the client.

Uses the response objectsgetWriter method to obtain areference to the PrintWriterobject that enables the servlet to send

content to the client.Create the XHTML document

by writing strings with theoutobjects println method.

26


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Outline

26


28

29 // head section of document


31 out.println( "A Simple Servlet Example" );


33

34 // body section of document


36 out.println( "Welcome to Servlets!" );


38

39 // end XHTML document40 out.println( "" );

41 out.close(); // close stream to complete the page

42 }

43 }

WelcomeServlet.java

(2 of 2)

Closes the output stream,

flushes the output buffer

and sends the information

to the client.

1


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Outline

WelcomeServlet.html

(1 of 1)

1

2

4

5

6

7

8

9 Handling an HTTP Get Request

10

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15

Click the button to invoke the servlet

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Outline

Program output



36.3.1 Setting Up the Apache Tomcat Server

Download Tomcat (version 4.1.27) jakarta.apache.org/site/binindex.cgi

Define environment variables JAVA_HOME

CATALINA_HOME

Start the Tomcat server startup

Launch the Tomcat server http://localhost:8080/



36.3.1 Setting Up the Apache Tomcat Server

(Cont.).

Fig. 36.7 Tomcat documentation home page. (Courtesy of The Apache Software Foundation.)



36.3.2 Deploying a Web Application

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



36.3.2 Deploying a Web Application (Cont.)

Directory Descriptioncontext root This is the root directory for the Web application. All the

JSPs, HTML documents, servlets and supporting files such

as images and class files reside in this directory or its

subdirectories. The name of this directory is specified by the

Web application creator. To provide structure in a Web

application, subdirectories can be placed in the context root.

For example, if your application uses many images, you

might place an images subdirectory in this directory. The

examples of this chapter use jhtp5 as the context root.WEB-INF This directory contains the Web application deployment

descriptor(web.xml).WEB-INF/classes This directory contains the servlet class files and other

supporting class files used in a Web application. If the

classes are part of a package, the complete package directory

structure would begin here.

WEB-INF/lib This directory contains Java archive (JAR) files. The JARfiles can contain servlet class files and other supporting class

files used in a Web application.

Fig. 36.8 Web application standard directories.

1


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2004 Prentice Hall, Inc.All rights reserved.

Outline

pp

2 "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"

3 "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">

4

5

6

7

8

9 Internet World Wide Web How to Program JSP

10 and Servlet Chapter Examples

11

12

13

14 This is the Web application in which we15 demonstrate our JSP and Servlet examples.

16

17

18

19

20 welcome1

21

22

23 A simple servlet that handles an HTTP get request.

24

25

web.xml

(1 of 2)

Element web-app defines the configurationof each servlet in the Web application and

the servlet mapping for each servlet.

Element display-name specifiesa name that can be displayed to the

administrator of the server on which

the Web application is installed.

Element description specifies adescription of the Web application

that might be displayed to the

administrator of the server.

Element servlet describes a servlet.Element servlet-name

is the name for the servlet.Element descriptionspecifies a description for

this particular servlet.

26


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Outline27 WelcomeServlet28

29

30

31

32

33 welcome1

34 /welcome1

35

36

37

web.xml

(2 of 2)Element servlet-mapping

specifies servlet-name andurl-pattern elements.

Element servlet-classspecifies compiled servlets

fully qualified class name.


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Invoke WelcomeServlet example /iw3htp3/welcome1 /iw3htp3 specifies the context root

/welcome1 specifies the URL pattern

URL pattern formats Exact match

/iw3htp3/welcome1

Path mappings

/iw3htp3/example/*

Extension mappings

*.jsp

Default servlet

/


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WelcomeServlet Web application directory and file structureiw3htp3servlets

WelcomeServlet.htmlWEB-INF

web.xmlclasses

WelcomeServlet.classFig. 36.10 Web application directory and file structure for

WelcomeServlet.


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36.4 Handling HTTP get RequestsContaining Data

Servlet WelcomeServlet2 Responds to a get request that contains data

1 // Fig. 36.11: WelcomeServlet2.java


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Outline2 // Processing HTTP get requests containing data.3



6 import java.io.*;

7

8 publicclass WelcomeServlet2 extends HttpServlet {

9

10 // process "get" request from client




14

{15 String firstName = request.getParameter( "firstname" );

16



19

20 // send XHTML document to client

21



24

WelcomeServlet2

(1 of 2)

The request objectsgetParametermethod receives the

parameter name and

returns the

correspondingStringvalue.

25 out.println( "


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Outline26 "XHTML 1.0 Strict//EN\" \"http://www.w3.org" +27 "/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );

28


30



33 out.println(

34 "Processing get requests with data" );


36


38out.println( "" );

39 out.println( "Hello " + firstName + ",
" );



42

43 // end XHTML document



46 }

47 }

WelcomeServlet2

(2 of 2)

Uses the result of line15 as part of the

response to the client.

1


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Outline2

4

5

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7

8

9 Processing get requests with data

10

11

12

13

14

15

16 Type your first name and press the Submit button

17

18

19

20

21

22

23

WelcomeServlet2

.html

(1 of 1)

Get the first name

from the user.


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Outline

Program output


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36.4 Handling HTTP get RequestsContaining Data (Cont.)

Descriptor elementValueservletelementservlet-name welcome2description Handling HTTP get requests with data.servlet-class WelcomeServlet2servlet-mappingelementservlet-name welcome2url-pattern /welcome2Fig. 36.13 Deployment descriptor information for servlet

WelcomeServlet2.


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36.5 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

O tli

1 // Fig. 36.14: WelcomeServlet3.java


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Outline2 // Processing post requests containing data.3



6 import java.io.*;

7

8 publicclass WelcomeServlet3 extends HttpServlet {

9

10 // process "post" request from client

11 protectedvoid doPost( HttpServletRequest request,



14{

15 String firstName = request.getParameter( "firstname" );

16



19

20 // send XHTML page to client

21



24

WelcomeServlet3

.java

(1 of 2)

Declare a doPost methodto responds to post requests.

O tli

25 out.println( "


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Outline26 "XHTML 1.0 Strict//EN\" \"http://www.w3.org" +27 "/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );

28


30



33 out.println(

34 "Processing post requests with data" );


36


38

out.println( "" );39 out.println( "Hello " + firstName + ",
" );



42




46 }

47 }

WelcomeServlet3

.java

(1 of 2)

O tli

1 2 !DOCTYPE ht l PUBLIC " //W3C//DTD XHTML 1 0 St i t//EN"


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Outline2

4

5

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7

8

9 Handling an HTTP Post Request with Data

10

11

12

13

14

15

16 Type your first name and press the Submit button

17

18

19

20

21

22

23

WelcomeServlet3

.html

(1 of 1)

Provide a form in which theuser can input a name in the

text input elementfirstname, then click theSubmit button to invokeWelcomeServlet3.

O tli


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Outline

Program output


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36.5 Handling HTTP post Requests (Cont.)

Descriptorelement Valueservletelementservlet-name welcome3description Handling HTTP post requests with

data.servlet-class WelcomeServlet3

servlet-mappingelementservlet-name welcome3url-pattern /welcome3Fig. 36.16 Deployment descriptor information for servlet

WelcomeServlet3.

36 6 R di ti R t t Oth


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36.6 Redirecting Requests to Other

Resources

Servlet RedirectServlet Redirects the request to a different resource

Outline

1 // Fig. 36.17: RedirectServlet.java

2 // R di cti g t diff t W b g


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Outline2 // Redirecting a user to a different Web page.3



6 import java.io.*;

7

8 publicclass RedirectServlet extends HttpServlet {

9

10 // process "get" request from client




14

{15 String location = request.getParameter( "page" );

16

17 if ( location != null )

18

19 if ( location.equals( "deitel" ) )

20 response.sendRedirect( "http://www.deitel.com" );

21 else

22 if ( location.equals( "welcome1" ) )

23 response.sendRedirect( "welcome1" );

24

RedirectServlet.java

(1 of 3)

Obtains the pageparameter from the request.

Determine if the value is either

deitel or welcome1Redirects the request to

www.deitel.com.

Redirects the request to the

servlet WelcomeServlet.

Outline

25 // code that executes only if this servlet26 // does not redirect the user to another page


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Outline26 // does not redirect the user to another page27



30



33


37

38

out.println(39 "" );

40



43 out.println( "Invalid page" );


45



48 out.println( "Invalid page requested" );


(2 of 3)

Output a Web page indicating that aninvalid request was made if method

sendRedirect is not called.

Outline

49 out.println( "

" );


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Outline50 \ servlets/RedirectServlet.html\ > );51 out.println( "Click here to choose again
" );

53




57 }

58 }


(3 of 3)

Outline

1 2


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Outline2

4

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9 Redirecting a Request to Another Site

10

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12

13

Click a link to be redirected to the appropriate page

14

15

16 www.deitel.com

17

18 Welcome servlet

19

20

21

RedirectServlet.html

(1 of 1)

Provide hyperlinks that allow

the user to invoke the servlet

RedirectServlet.

Outline


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Outline

Program output

36 6 Redirecting Requests to other


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36.6 Redirecting Requests to other

Resources (Cont.)

Descriptor

elementValue

servletelementservlet-name

redirect

descriptionRedirecting to static Web pages and otherservlets.

servlet-class

com.deitel.iw3htp3.servlets.RedirectServlet

servlet-mappingelementservlet-name

redirect

url-pattern/redirectFig. 36.19 Deployment descriptor information for servlet

RedirectServlet.

36 7 Multi Tier Applications: Using JDBC


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36.7 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

MS Access database

Outline

1 // Fig. 36.20: SurveyServlet.java2 // A Web-based survey that uses JDBC from a servlet.


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Outline// A Web based survey that uses JDBC from a servlet.3 package com.deitel.iw3htp3.servlets;

4

5 import java.io.*;

6 import java.text.*;

7 import java.sql.*;



10

11 public class SurveyServlet extends HttpServlet {

12 private Connection connection;

13 private Statement statement;

14

15 // set up database connection and create SQL statement

16 public void init( ServletConfig config ) throws ServletException

17 {

18 // attempt database connection and create Statements

19 try {

20 Class.forName( config.getInitParameter( "databaseDriver" ) );

21 connection = DriverManager.getConnection(22 config.getInitParameter( "databaseName" ) );

23

SurveyServlet.java

(1 of 6)

Servlets are initialized by

overriding method init.

Attempt to open a connection to

the animalsurvey database.

Loads the

database driver.

Outline

24 // create Statement to query database25 statement = connection.createStatement();

Create Statement tod t b


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Outline();26 }

27

28 // for any exception throw an UnavailableException to

29 // indicate that the servlet is not currently available

30 catch ( Exception exception ) {

31 exception.printStackTrace();

32 throw new UnavailableException(exception.getMessage());

33 }

34

35 } // end of init method

36

37

// process survey response38 protected void doPost( HttpServletRequest request,



41 {

42 // set up response to client


44 PrintWriter out = response.getWriter();45 DecimalFormat twoDigits = new DecimalFormat( "0.00" );

46



49

SurveyServlet.java

(2 of 6)

query database.

Outline

50 out.println( "


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Outline// \ \ p // g52 "/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );

53

54 out.println(

55 "" );

56



59

60 // read current survey response

61 int value =

62 Integer.parseInt( request.getParameter( "animal" ) );

63

String query;64

65 // attempt to process a vote and display current results

66 try {

67

68 // update total for current survey response

69 query = "UPDATE surveyresults SET votes = votes + 1 " +

70 "WHERE id = " + value;71 statement.executeUpdate( query );

72

SurveyServlet.java

(3 of 6)

Obtain the survey

response

Create query to update total

for current survey response

Execute queryto update total

for current survey response

Outline

73 // get total of all survey responses74 query = "SELECT sum( votes ) FROM surveyresults";

Create query to get total of all

E l f


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Outlineq y y75 ResultSet totalRS = statement.executeQuery( query );

76 totalRS.next();

77 int total = totalRS.getInt( 1 );

78

79 // get results

80 query = "SELECT surveyoption, votes, id FROM surveyresults " +

81 "ORDER BY id";

82 ResultSet resultsRS = statement.executeQuery( query );

83 out.println( "Thank you!" );


85


87 out.println( "

Thank you for participating." );

88 out.println( "
Results:
" );
89

90 // process results

91 int votes;

92

93 while ( resultsRS.next() ) {94 out.print( resultsRS.getString( 1 ) );

95 out.print( ": " );

96 votes = resultsRS.getInt( 2 );

97 out.print( twoDigits.format(

98 ( double ) votes / total * 100 ) );

SurveyServlet.java

(4 of 6)

survey responsesExecute queryto get total of

all survey responses

Create query to getsurvey results

Execute query to get

survey results

Outline

99 out.print( "% responses: " );100 out.println( votes );


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Outline101 }

102

103 resultsRS.close();

104

105 out.print( "Total responses: " );

106 out.print( total );

107



110 out.close();

111

112 } // end try

113

114 // if database exception occurs, return error page

115 catch ( SQLException sqlException ) {

116 sqlException.printStackTrace();

117 out.println( "Error" );


119 out.println( "

Database error occurred. " );120 out.println( "Try again later.
" );
121 out.close();

122 }

123

124 } // end of doPost method

SurveyServlet.java

(5 of 6)

OutlineM h d d l

125

126 // close SQL statements and database when servlet terminates


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Outline

SurveyServlet.java

(6 of 6)

Method destroy closes

Statement anddatabase connection.

127 public void destroy()

128 {

129 // attempt to close statements and database connection

130 try {

131 statement.close();

132 connection.close();

133 }

134

135 // handle database exceptions by returning error to client

136 catch ( SQLException sqlException ) {

137 sqlException.printStackTrace();

138 }

139 }

140

141 } // end class SurveyServlet

Outline

1 2


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Outline3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

4

5

6

7

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9 Survey

10

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12

13

14

15

What is your favorite pet?

16

17

18 Dog

20 Cat
22 Bird

24 Snake

Survey.html

(1 of 2)

Outline

26 None


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Outline28

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31

32

33

34

Survey.html

(2 of 2)

Outline


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Outline

36 7 Multi-Tier Applications: Using JDBC


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36.7 Multi-Tier Applications: Using JDBC

from a Servlet (Cont.)

Descriptor element

Valueservletelement

servlet-name animalsurvey

description Connecting to a database from a servlet.

servlet-class com.deitel.iw3htp3.servlets.SurveyServlet

init-param

param-name databaseDriverparam-value sun.jdbc.odbc.JdbcOdbcDriver

init-param

param-name databaseName

param-value jdbc:odbc:animalsurvey

servlet-mappingelement

servlet-name animalsurveyurl-pattern /animalsurvey

Fig. 36.22 Deployment descriptor information for servlet SurveyServlet.


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36.8 Web Resources

Servlet resources java.sun.com/products/servlet/index.html

www.servlets.com

www.servletsource.com

www.servletforum.com

www.coolservlets.com

5.1 servlets n http request

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