JavaServer Pages and Servlets

1
Chapter 25

• JavaServer Pages and Servlets

2
CHAPTER GOALS

• To implement dynamic web pages with JavaServer
  Pages technology
  
• To learn the syntactical elements of JavaServer
  Pages
  
• To structure a web application as a sequence of
  JavaServer Pages
  
• To understand the relationship between JavaServer
  Pages and servlets

3
Dynamic Web Content

• You can use JavaServer Pages (JSP) to implement
  dynamic web pages
  
• To use JSP's you need a web server that is
  integrated with a JSP container
  
• Apache Tomcat server is free

4
Dynamic Web Content

• A JavaServer Pages (JSP) page contains HTML tags
  and Java instructions
  
• The Java instructions are executed each time the
  page is served to the browser
  
• An instruction to insert the current date and
  time into a web page
  

5
File date.jsp

• 01
• 02
• 03 Date JSP
• 04
• 05
• 06 Date JSP
• 07 The current time is
• 08
• 09
• 10
• 11
• 12

6
Executing the Date Page
7
To Deploy the Date Page

• 1. Type the JSP file into a text editor
• 2. Place the file into a web application
  directory of your JSP engine
  
• 3. If you use Tomcat, create a subdirectory for
  the JSP file
  
• c\jakarta-tomcat\webapps\bigjava
• 4. Place the date.jsp file into that directory
• 5. Start the web server
• 6. Point your browser to
• localhost8080/bigjava/date.jsp

8
Dynamic Web Content

• The JSP container reads the requested JSP page
  and transforms it into an HTML page
  
• Regular HTML tags are left unchanged
• JSP tags ( ) are processed
• Expressions enclosed in JSP tags are evaluated
  and converted to a string using toString method

9
Dynamic Web Content

• The string is inserted into the HTML page
• The resulting document contains only HTML
• The web server sends the document to the
  browser

10
The JSP Container Rewrites the Requested Page
11
Encapsulating Computations in JavaBeans

• Most professional web pages need input from
  two different experts
  
• A programmer who understands how to compute
  the results the page will display
  
• A graphics designer who determines how to
  display the results
  
• It is best to keep the Java code and the HTML
  tags separate
  
• Any nontrivial computation should be carried
  out in a separate Java class
  
• You connect one or more JavaBeans to a JSP page

12
Encapsulating Computations in JavaBeans

• A JavaBean is a Java class
• It must have a default constructor
• A JavaBean exposes its properties through get
  and set methods
  
• Properties are accessed and modified by methods
  that follow a naming convention

13
Encapsulating Computations in JavaBeans

• If the property name is propertyName and the
  type is Type
  
• accessor method
• Type getPropertyName()
• mutator method
• void setpropertyName(Type newValue)
• A boolean property uses a different convention
• boolean isPropertyName()
• void setPropertyName(boolean newValue)
• By convention the name of the bean ends in Bean
  
  
• Do not make any assumptions about the internal
  representation of the data

14
Encapsulating Computations in JavaBeans

• A JSP page gives you access to a JavaBean's
  properties without having to write Java code.
  
• To use a bean in a JSP page, use the
  jspuseBean directive
  
• Give a name to the object and specify the class
  name of the bean
  
• This directive invokes the default constructor
  of the PersonBean class
  
• It makes an object with name user

15
Encapsulating Computations in JavaBeans

• To set a property in the bean, use the
  setProperty directive
  
• value"true"/
  
• To get a property in the bean, use the
  getProperty directive
  
• 
  
  
• This returns a string that becomes part of the
  HTML page

16
Encapsulating Computations in JavaBeans

• We want to display just the current time, not
  the whole date
  
• Get the time with the getTimeInstance method of
  the DateFormat class
  
• Put this code in a bean class

17

• File TimeFormatterBean.Java

01 import java.text.DateFormat
02 import java.util.Date 03 04 / 05
This bean formats the time of day from a given
date. 06 / 07 public class TimeFormatterBean
08 09 / 10 Initializes the
formatter. 11 / 12 public TimeFormatter
Bean() 13 14 timeFormatter DateFo
rmat.getTimeInstance() 15 16 17 /
18 Write-only date property. 19
_at_param aDate the date to be formatted.
18
20 / 21 public void setDate(Date aDate)
22 23 theDate aDate 24
25 26 / 27 Read-only time prop
erty. 28 _at_return the formatted time 29
/ 30 public String getTime() 31 32
String timeString timeFormatter.format(t
heDate) 33 return timeString 34
35 36 private DateFormat timeFormatter 37
private Date theDate 38
19

• File time.jsp

01 class"TimeFormatterBean"/ 02
name"formatter" property"date" value"
java.util.Date() "/ 03 04
05 Time JSP 06
07 08 Time JSP 09
The current time is
10
property"time"/ 11 12
13 14
20
Encapsulating Computations in JavaBeans

• It is a good idea to put the bean directive at
  the beginning of the JSP file, before the HTML
  
• Both time.jsp and TimeFormatterBean must be
  deployed to the proper directories
  
• time.jsp into
• c\Jakarta-tomcat\webapps\bigjava
• TimeFormatterBean into
• c\Jakarta-tomcat\webapps\bigjava\WEB-INF\classes
  
  
• You use JavaBeans to separate HTML presentation
  from Java computation

21
Handling Request Parameters

• Modify the JSP page to take as input the user's
  city and to return the time in that time zone
  
• The Java library contains a TimeZone class that
  knows about time zones
  
• A time zone is identified by a string such as
• "America/Los_Angeles"
• "Asia/Tokyo"
• The static method getAvailableIDs returns a
  string array containing all IDs
  
• The static getTimeZone method returns a
  TimeZone class for a given ID string
  
• String zoneID "America/Los_Angeles"
• TimeZone zone TimeZone.getTimeZone(zoneID)

22
Handling Request Parameters

• The user will enter a city like Los Angeles
• Our time zone bean will check whether that
  string appears at the end of one of the time zone
  ID's
  
• The JSP page formats the current time in that
  time zone
  
• Or prints a message that the city name is not
  found

23
Handling Request Parameters

• We need an HTML form to get the user input
• The form will have a textfield and a button to
  submit the form to the JSP

24

• File timezone.html

01 02 03 Time
Zone Form 04 05
06 07
City 08
t" name"city"/ 09
bmit" value"Get Time"/ 10 11
12 13
25
The HTML Form for Entering City Names
26
Handling Request Parameters

• When a browser submits a form, it sends the
  names and values of all form elements to the web
  server
  
• The name is city
• the value is the contents of the text field
• The action attribute of the form element
  specifies the URL of the server-side program that
  processes the form
  
• In this case timezone.jsp
• In a JSP page, you can access the form data
  through the predefined request object
  
• The getParameter method of the ServletRequest
  class returns the value of the form element with
  a given name
  
• To get the city that the user typed

27
Handling Request Parameters

• To set the city property in the TimeZoneBean
  value" /
  
• A convenient shorthand
• param"city"/

28

• File timezone.jsp

01
02
value""/
03
param"city"/ 04 05
itleTime Zone JSP 06 07
08 Time Zone JSP 09
The current time in
("city") is 10
e"zone" property"time"/ 11 12
13
29
File TimeZoneBean.java

• 01 import java.text.DateFormat
• 02 import java.util.Date
• 03 import java.util.TimeZone
• 04
• 05 /
• 06 This bean formats the local time of day
  for a given date
  
• 07 and city.
• 08 /
• 09 public class TimeZoneBean
• 10
• 11 /
• 12 Initializes the formatter.
• 13 /
• 14 public TimeZoneBean()
• 15
• 16 timeFormatter DateFormat.getTimeInstan
  ce()
  
• 17

30

• 18
• 19 /
• 20 Write-only date property.
• 21 _at_param aDate the date to be formatted.
• 22 /
• 23 public void setDate(Date aDate)
• 24
• 25 theDate aDate
• 26
• 27
• 28 /
• 29 Write-only city property.
• 30 _at_param aCity the city for which to
  report the local time
  
• 31 /
• 32 public void setCity(String aCity)
• 33
• 34 city aCity
• 35
• 36

31

• 38 Read-only available property.
• 39 _at_return true if time zone information
  is available for
  
• 40 this city.
• 41 /
• 42 public boolean isAvailable()
• 43
• 44 return getTimeZone(city) ! null
• 45
• 46
• 47 /
• 48 Read-only time property.
• 49 _at_return the formatted time
• 50 /
• 51 public String getTime()
• 52
• 53 TimeZone zone getTimeZone(city)
• 54 if (zone null) return "not
  available"
  
• 55 timeFormatter.setTimeZone(zone)
• 56 String timeString timeFormatter.format
  (theDate)
  

32

• 58
• 59
• 60 /
• 61 Looks up the time zone for a city
• 62 _at_param aCity the city for which to find
  the time zone
  
• 63 _at_return the time zone or null if no
  match is found
  
• 64 /
• 65 private static TimeZone getTimeZone(String
  city)
  
• 66
• 67 String ids TimeZone.getAvailableIDs(
  )
  
• 68 for (int i 0 i
• 69 if (timeZoneIDmatch(idsi, city))
• 70 return TimeZone.getTimeZone(idsi
  )
  
• 71 return null
• 72
• 73
• 74 /
• 75 Checks whether a time zone ID matches a
  city
  
• 76 _at_param id the time zone ID (e.g.
  "America/Los_Angeles")
  

33

• 78 _at_return true if the ID and city match
• 79 /
• 80 private static boolean timeZoneIDmatch(Stri
  ng id, String city)
  
• 81
• 82 String idCity id.substring(id.indexOf(
  '/') 1)
  
• 83 return idCity.replace('_', '
  ').equals(city)
  
• 84
• 85
• 86 private DateFormat timeFormatter
• 87 private Date theDate
• 88 private String city
• 89

34
The Output of the Time Zone JSP Page
previous start next
previous start next
35
HTML Forms

• An HTML form contains user interface elements
  such as
  
• o Text fields
• o Password fields
• o Text areas
• o Radio buttons
• o Check boxes
• o Selection lists
• o Submit buttons
• o Hidden fields

36
The HTML Form Elements
37
HTML Forms

• Most form elements have the syntax
• You should include a name attribute on every
  element except submit button
  
• You may include a value attribute with a
  default value

38
HTML Forms

• Text field
• value"USA" size"16" maxlength"16" /
  
• Password
• size"16" maxlength"16" /
  
• Text area
• 
  default text
  

39
HTML Forms

• Radio button
• value"S"/Small
  
• value"M"/Medium
  
• checked"checked"/Large
  
• value"XL"/Extra large
  
• Only one radio button can be checked at a
  time
  
• Check box
• value"mushrooms" checked"checked"/Mushrooms
  
  
• value"anchovies" /Anchovies
  
• More than one checkbox in a group can have
  the checked attribute set to "checked"
  
• If both boxes are checked the browser sends
  the server toppingsmushroomstoppingsanchovies

40
HTML Forms

• Selection list
• Januarytion February
  
• March
• April
• .
• .
• .
• December

41

• Submit button
• Hidden field
• value"YYY-11543-234-9"/
  
• The browser does not display a hidden field
• It sends the name/value pairs in the field to
  the server when the form is submitted

42
HTML Forms

• Place all elements that belong to a form into a
  form element method"POST"
  
• .
• .
• .
• An HTML form must specify the URL of the server
  program that processes the form data
  
• The action attribute contains the URL
• Set the method attribute to POST because it has
  no length
  
• limit

43
Session Tracking

• A session is a sequence of page requests from the
  same browser to the same web server
  
• To track a session in a sequence of JSP pages,
  use a bean with session scope
  
• scope"session"/
  
• The user requests the JSP page containing this
  directive for the first time
  
• A new cart object is constructed
• The user returns to the same page or visits
  another page in the same application
  
• The cart object is still alive
• If the bean directive has no scope attribute
• The bean object has page scope
• A new object is created every time the page is
  visited

44
Session Tracking

• Create a program that allows the user to keep
  adding cities and their time zones
  
• In the initial HTML form, the web application
  asks for the name of the first city
  
• The JSP page displays the first city and a form
  to enter another city
  
• The user can add as many cities as he likes
• All cities are stored in an object of the
  MultiZoneBean class

45
Session Tracking

• The bean object has session scope and so holds a
  list of all the cities
  
• Keep cities in a MultiZoneBean
• scope"session"/
  
• An instance is created for each session
• The setCity method adds a city to the bean object
  
  
• The new city is the value of the text field whose
  name is city
  
• param"city"/

46
Asking for the First of Several Cities
47
Asking for the Next City
48
Display the Time in Multiple Locations
49
File multizone.html

• 01
• 02
• 03 Multiple Time Zone Form
• 04
• 05
• 06
• 07 method"POST"
• 08 First City
• 09
• 10 City"/
  
• 11
• 12
• 13
• 14

50
File multizone.jsp

• 01 scope"session"/
  
• 02 value""/
  
• 03 param"city"/
  
• 04 value"
  property\"times\"/"/
  
• 05
• 06
• 07
• 08 Multiple Time Zone JSP
• 09
• 10
• 11 Current time lookup
• 12
  • 13 property"times"/
    
  • 14

51

• 15
• 16 method"POST"
• 17 Next City
• 18
• 19 City"/
  
• 20
• 21
• 22
• 23

52
File MultiZoneBean.java

• 01 import java.text.DateFormat
• 02 import java.util.ArrayList
• 03 import java.util.Date
• 04 import java.util.TimeZone
• 05
• 06 /
• 07 This bean formats the local times of day
  for a given date
  
• 08 and list of cities.
• 09 /
• 10 public class MultiZoneBean
• 11
• 12 /
• 13 Initializes the formatter and city
  list.
  
• 14 /
• 15 public MultiZoneBean()
• 16
• 17 timeFormatter DateFormat.getTimeInstan
  ce()

53

• 18 cities new ArrayList()
• 19
• 20
• 21 /
• 22 Write-only date property.
• 23 _at_param aDate the date to be formatted.
• 24 /
• 25 public void setDate(Date aDate)
• 26
• 27 theDate aDate
• 28
• 29
• 30 /
• 31 Write-only city property.
• 32 _at_param aCity the city to add to the
  city list
  
• 33 /
• 34 public void setCity(String aCity)
• 35
• 36 cities.add(aCity)

54

• 38
• 39 /
• 40 Read-only times property.
• 41 _at_return a string containing the HTML
  code for an unnumbered
  
• 42 list of cities and local times
• 43 /
• 44 public String getTimes()
• 45
• 46 StringBuffer buffer new
  StringBuffer()
  
• 47 for (int i 0 i i)
  
• 48
• 49 String city (String)cities.get(i)
  
• 50
• 51 buffer.append("
• ")
• 52 buffer.append(city)
• 53 buffer.append(" ")
• 54
• 55 TimeZone zone getTimeZone(city)
• 56 if (zone null)

55

• 58 else
• 59
• 60 timeFormatter.setTimeZone(zone)
• 61 String timeString
  timeFormatter.format(theDate)
  
• 62 buffer.append(timeString)
• 63
• 64 buffer.append("
")
• 65
• 66 return buffer.toString()
• 67
• 68
• 69 /
• 70 Looks up the time zone for a city
• 71 _at_param aCity the city for which to find
  the time zone
  
• 72 _at_return the time zone or null if no
  match is found
  
• 73 /
• 74 private static TimeZone getTimeZone(String
  city)
  
• 75
• 76 String ids TimeZone.getAvailableIDs(
  )
  

56

• 78 if (timeZoneIDmatch(idsi, city))
• 79 return TimeZone.getTimeZone(idsi
  )
  
• 80 return null
• 81
• 82
• 83 /
• 84 Checks whether a time zone ID matches a
  city
  
• 85 _at_param id the time zone ID (e.g.
  "America/Los_Angeles")
  
• 86 _at_param aCity the city to match (e.g.
  "Los Angeles")
  
• 87 _at_return true if the ID and city match
• 88 /
• 89 private static boolean timeZoneIDmatch(Stri
  ng id, String city)
  
• 90
• 91 String idCity id.substring(id.indexOf(
  '/') 1)
  
• 92 return idCity.replace('_', '
  ').equals(city)
  
• 93
• 94
• 95 private DateFormat timeFormatter
• 96 private Date theDate

57

• Branching and Forwarding Pages

• A JSP page can forward a request to another
  page
  
• You can use forwarding to implement branches
• Post the query to a JSP page that checks the
  input but has no HTML output
  
• The page evaluates the input and uses the
  jspforward directive to select another page

58

• Branching and Forwarding Pages

• The forward directive has the format
• It causes the JSP engine to load the page at
  the URL
  
• The request data of the current bean and beans
  with scope"request" are forwarded to new page
  
• Branch and forward page
• if (some condition)
• else

59

• Branching and Forwarding Pages

• We can use this technique to handle cities for
  which no time zone is known
  
• Start with the same HTML form
• Use the same html
• Except post the data to a non-visual JSP page
• This page then forwards the request to the
  proper page

60
File zonebranch.html

• 01
• 02
• 03 Time Zone Branch Form
• 04
• 05
• 06
• 07 City
• 08
  
  
• 09 Time"/
  
• 10
• 11
• 12
• 13

61
File zonebranch.jsp

• 01 scope"request"/
  
• 02 value""/
  
• 03 param"city"/
  
• 04
• 05 if (zone.isAvailable())
• 06
• 07
• 08
• 09
• 10
• 11 else
• 12
• 13
• 14
• 15
• 16
• 17

62
File zoneresult.jsp

• 01
• 02
• 03 Time Zone Branch Result
  JSP
  
• 04
• 05
• 06 Time Zone Branch Result JSP
• 07 The current time in request.getParameter("city") is
  
• 08 property"time"/
  
• 09
• 10
• 11

63
File zoneerror.jsp

• 01
• 02
• 03 Time Zone Error JSP
• 04
• 05
• 06 Unfortunately, no information is
  available for
  
• 07 .
  Please enter
  
• 08 another city.
• 09
• 10
• 11 City
• 12
  
  
• 13 Time"/
  
• 14
• 15
• 16
• 17

64
A Three-Tier Application

• The presentation tier the web browser
• The business logic tier the JSP engine, JSP
  pages, and the JavaBean
  
• The storage tier the database

65
A Three-Tier Application

• Database table CityZone
• ZoneDBBean consults this database to find the
  user requested city
  
• If not available, it looks through the ID's as
  MultiZoneBean did
  
• Use a DataSourceBean to manage the database
  connection

66
A Three-Tier Application

• Only one instance of DataSourceBean needed for
  all JSP pages that make up the web application
  
• Set its scope to "application"
• Store the database properties in the file
  web.xml in the WEB_INF subdirectory
  
• The JSP pages can access the information in
  web.xml
  
• Use the getInitParameter method of the
  predefined application object

67
A Three-Tier Application

• Retrieve the database information from web.xml
  and initialize the database
  
• Any directives you place as child elements of
  the jspuseBean element are executed only once
  
• ZoneDBBean makes a database query to find the
  requested city

68
File zonedb.html

• 01
• 02
• 03 Time Zone Database Form
• 04
• 05
• 06 method"POST"
  
• 07 City
• 08
• 09 Time"/
  
• 10
• 11
• 12
• 13

69

• File zonedb.jsp

01 scope"application" 02
"db" property"driver" 03 value'
lication.getInitParameter("jdbc.drivers") '/
04
05 value'
r("jdbc.url") '/ 06
"db" property"username" 07 value'
plication.getInitParameter("jdbc.username")
'/ 08
"password" 09 value'
nitParameter("jdbc.password") '/
10 11 12
e" class"ZoneDBBean"/ 13
"zone" property"city" param"city"/
14
property"connection" value"
db.getConnection() "/ 15
e"zone" property"date" value"
java.util.Date() "/ 16
70
17 18 19 Zone D
atabase JSP 20 21
22 Zone Database JSP 23
The current time in
ity") is 24
zone" property"time"/ 25 26
body 27
71
File DataSourceBean.Java

• 01 import java.sql.DriverManager
• 02 import java.sql.Connection
• 03 import java.sql.SQLException
• 04
• 05 /
• 06 A simple data source bean for getting
  database connections.
  
• 07 /
• 08 public class DataSourceBean
• 09
• 10 /
• 11 Write-only driver property.
• 12 _at_param driver the database driver name
• 13 /
• 14 public void setDriver(String driver)
• 15 throws ClassNotFoundException
• 16
• 17 Class.forName(driver)

72

• 18
• 19
• 20 /
• 21 Write-only url property.
• 22 _at_param aUrl the JDBC URL
• 23 /
• 24 public void setUrl(String aUrl)
• 25
• 26 url aUrl
• 27
• 28
• 29 /
• 30 Write-only username property.
• 31 _at_param aUsername the database user
  name
  
• 32 /
• 33 public void setUsername(String aUsername)
• 34
• 35 username aUsername
• 36

73

• 38 /
• 39 Write-only password property.
• 40 _at_param aUsername the database user's
  password
  
• 41 /
• 42 public void setPassword(String aPassword)
• 43
• 44 password aPassword
• 45
• 46
• 47 /
• 48 Gets a connection to the database.
• 49 _at_return the database connection
• 50 /
• 51 public static Connection getConnection()
• 52 throws SQLException
• 53
• 54 return
• 55 DriverManager.getConnection(url,
  username, password)
  
• 56

74

• 58 private static String url
• 59 private static String username
• 60 private static String password
• 61

75
File ZoneDBBean.Java

• 001 import java.text.DateFormat
• 002 import java.util.Date
• 003 import java.util.TimeZone
• 004 import java.sql.Connection
• 005 import java.sql.Statement
• 006 import java.sql.ResultSet
• 007 import java.sql.SQLException
• 008
• 009 /
• 010 This bean formats the local time of day
  for a given date
  
• 011 and city, consulting a database in
  addition to the standard
  
• 012 time zone ID list.
• 013 /
• 014 public class ZoneDBBean
• 015
• 016 /
• 017 Initializes the formatter.

76

• 018 /
• 019 public ZoneDBBean()
• 020
• 021 timeFormatter DateFormat.getTimeInsta
  nce()
  
• 022
• 023
• 024 /
• 025 The city property.
• 026 _at_return the city for which to report
  the local time
  
• 027 /
• 028 public String getCity()
• 029
• 030 return city
• 031
• 032
• 033 /
• 034 The city property.
• 035 _at_param aCity the city for which to
  report the local time
  
• 036 /

77

• 038
• 039 city aCity
• 040
• 041
• 042 /
• 043 Write-only date property.
• 044 _at_param aDate the date to be
  formatted.
  
• 045 /
• 046 public void setDate(Date aDate)
• 047
• 048 theDate aDate
• 049
• 050
• 051 /
• 052 Read-only time property.
• 053 _at_return the formatted time
• 054 /
• 055 public String getTime() throws
  SQLException
  
• 056

78

• 058 zone getTimeZoneDB()
• 059 if (zone null) // not found in
  database
  
• 060 zone getTimeZone(city)
• 061 if (zone null) return "not
  available"
  
• 062 timeFormatter.setTimeZone(zone)
• 063 return timeFormatter.format(theDate)
  
  
• 064
• 065
• 066 /
• 067 Looks up the time zone for a city in
  the database and
  
• 068 the list of time zone IDs.
• 069 _at_param aCity the city for which to
  find the time zone
  
• 070 _at_return the time zone or null if no
  match is found
  
• 071 /
• 072 private TimeZone getTimeZoneDB() throws
  SQLException
  
• 073
• 074 Connection conn null
• 075 try
• 076

79

• 078 Statement stat conn.createStatemen
  t()
  
• 079 String query "SELECT Zone FROM
  CityZone"
  
• 080 " WHERE City '" city
  "'"
  
• 081 ResultSet result
  stat.executeQuery(query)
  
• 082 if (result.next())
• 083 return TimeZone.getTimeZone(resul
  t.getString(1))
  
• 084 else
• 085 return null
• 086
• 087 finally
• 088
• 089 if (conn ! null) conn.close()
• 090
• 091
• 092
• 093 /
• 094 Looks up the time zone for a city in
  the list of time
  
• 095 zone IDs
• 096 _at_param aCity the city for which to
  find the time zone
  

80

• 098 /
• 099 private static TimeZone
  getTimeZone(String city)
  
• 100
• 101 String ids TimeZone.getAvailableIDs
  ()
  
• 102 for (int i 0 i
• 103 if (timeZoneIDmatch(idsi, city))
• 104 return TimeZone.getTimeZone(idsi
  )
  
• 105 return null
• 106
• 107
• 108 /
• 109 Checks whether a time zone ID matches
  a city
  
• 110 _at_param id the time zone ID (e.g.
  "America/Los_Angeles")
  
• 111 _at_param aCity the city to match (e.g.
  "Los Angeles")
  
• 112 _at_return true if the ID and city match
• 113 /
• 114 private static boolean timeZoneIDmatch(Str
  ing id, String city)
  
• 115
• 116 String idCity id.substring(id.indexOf
  ('/') 1)
  

81

• 118
• 119
• 120 private Date theDate
• 121 private DateFormat timeFormatter
• 122 private String city
• 123

82
Servlets

• Servlets are an alternative to JSPs for
  building web applications
  
• JSP pages are actually translated into Servlets
  
  
• A servlet is a Java program
• It carries out computations
• And can emit data that is returned to the
  browser

83
Servlets

• A servlet is a class that extends HTTPServlet
  class
  
• To handle GET requests, a servlet implements
  doGet
  
• void doGet( HttpServletRequest request,
  HttpServletResponse response)
  
• To handle POST requests, a servlet implements
  doPost
  
• void doPost( HttpServletRequest request,
  HttpServletResponse response)

84
Servlets

• This example does not receive any request
  information
  
• The servlet
• Obtains the current time
• Creates HTML document containing the
  information
  
• Sends the page back to the browser

85
Servlets

• The request parameter contains information about
  the request
  
• Not used in this example
• The response parameter lets you specify what to
  send back to the browser

86
Servlets

• To send an HTML document back to the browser
• Set the content type of the response to HTML
  response.setContentType("text/html")
  
• Get a print writer to collect the document to be
  sent PrintWriter out response.getWriter()
  
• Print the HTML document to the print writer
• Close the print writer

87

• File DateServlet.Java

01 import java.io.PrintWriter
02 import java.io.IOException