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Chapter 25 JavaServer Pages and Servlets. CHAPTER GOALS To implement dynamic web pages with JavaServer Pages technology To learn the syntactical elements.

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Presentation on theme: "Chapter 25 JavaServer Pages and Servlets. CHAPTER GOALS To implement dynamic web pages with JavaServer Pages technology To learn the syntactical elements."— Presentation transcript:

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 localhost:8080/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 o A programmer who understands how to compute the results the page will display o 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 o accessor method Type getPropertyName() o 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 jsp:useBean 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 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 TimeFormatterBean() 13: { 14: timeFormatter = DateFormat.getTimeInstance(); 15: } 16: 17: /** 18: Write-only date property. 19: @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 property. 28: @return the formatted time 29: */ 30: public String getTime() 31: { 32: String timeString = timeFormatter.format(theDate); 33: return timeString; 34: } 35: 36: private DateFormat timeFormatter; 37: private Date theDate; 38: }

19 File time.jsp 01: 02: "/> 03: 04: 05: Time JSP 06: 07: 08: Time JSP 09: The current time is: 10: 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 o "America/Los_Angeles" o "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: 09: 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 o The name is city o 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 o 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 o

27 Handling Request Parameters To set the city property in the TimeZoneBean /> A convenient shorthand

28 File timezone.jsp 01: 02: "/> 03: 04: 05: Time Zone JSP 06: 07: 08: Time Zone JSP 09: The current time in is: 10: 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.getTimeInstance(); 17: }

30 18: 19: /** 20: Write-only date property. 21: @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: @param aCity the city for which to report the local time 31: */ 32: public void setCity(String aCity) 33: { 34: city = aCity; 35: } 36: 37: /**

31 38: Read-only available property. 39: @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: @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); 57: return timeString;

32 58: } 59: 60: /** 61: Looks up the time zone for a city 62: @param aCity the city for which to find the time zone 63: @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 < ids.length; i++) 69: if (timeZoneIDmatch(ids[i], city)) 70: return TimeZone.getTimeZone(ids[i]); 71: return null; 72: } 73: 74: /** 75: Checks whether a time zone ID matches a city 76: @param id the time zone ID (e.g. "America/Los_Angeles") 77: @param aCity the city to match (e.g. "Los Angeles")

33 78: @return true if the ID and city match 79: */ 80: private static boolean timeZoneIDmatch(String 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 previousprevious | start | nextstartnext previousprevious | start | nextstartnext

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 Password Text area default text

39 HTML Forms Radio button Small Medium Large Extra large o Only one radio button can be checked at a time Check box Mushrooms Anchovies o More than one checkbox in a group can have the checked attribute set to "checked" o If both boxes are checked the browser sends the server toppings=mushrooms+toppings=anchovies

40 HTML Forms Selection list January February March April. December

41 Submit button Hidden field o The browser does not display a hidden field o 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. 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 The user requests the JSP page containing this directive for the first time oA new cart object is constructed The user returns to the same page or visits another page in the same application oThe cart object is still alive If the bean directive has no scope attribute oThe bean object has page scope oA 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 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

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:

08: First City: 09: 10: 11: 12: 13: 14:

50 File multizone.jsp 01: 02: "/> 03: 04: "/> 05: 06: 07: 08: Multiple Time Zone JSP 09: 10: 11: Current time lookup 12: 13: 14:

51 15: 17: Next City: 18: 19: 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.getTimeInstance();

53 18: cities = new ArrayList(); 19: } 20: 21: /** 22: Write-only date property. 23: @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: @param aCity the city to add to the city list 33: */ 34: public void setCity(String aCity) 35: { 36: cities.add(aCity); 37: }

54 38: 39: /** 40: Read-only times property. 41: @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 < cities.size(); 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) 57: buffer.append("not available");

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: @param aCity the city for which to find the time zone 72: @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(); 77: for (int i = 0; i < ids.length; i++)

56 78: if (timeZoneIDmatch(ids[i], city)) 79: return TimeZone.getTimeZone(ids[i]); 80: return null; 81: } 82: 83: /** 84: Checks whether a time zone ID matches a city 85: @param id the time zone ID (e.g. "America/Los_Angeles") 86: @param aCity the city to match (e.g. "Los Angeles") 87: @return true if the ID and city match 88: */ 89: private static boolean timeZoneIDmatch(String 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; 97: private ArrayList cities; 98: }

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 jsp:forward 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: 10: 11: 12: 13:

61 File zonebranch.jsp 01: 02: "/> 03: 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 is: 08: 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: 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 jsp:useBean 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: 07: City: 08: 09: 10: 11: 12: 13:

69 File zonedb.jsp 01: 02: 04: 06: 08: 10: 11: 12: 13: 14: "/> 15: "/> 16:

70 17: 18: 19: Zone Database JSP 20: 21: 22: Zone Database JSP 23: The current time in is: 24: 25: 26: 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: @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: @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: @param aUsername the database user name 32: */ 33: public void setUsername(String aUsername) 34: { 35: username = aUsername; 36: } 37:

73 38: /** 39: Write-only password property. 40: @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: @return the database connection 50: */ 51: public static Connection getConnection() 52: throws SQLException 53: { 54: return 55: DriverManager.getConnection(url, username, password); 56: } 57:

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.getTimeInstance(); 022: } 023: 024: /** 025: The city property. 026: @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: @param aCity the city for which to report the local time 036: */ 037: public void setCity(String aCity)

77 038: { 039: city = aCity; 040: } 041: 042: /** 043: Write-only date property. 044: @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: @return the formatted time 054: */ 055: public String getTime() throws SQLException 056: { 057: TimeZone zone = null;

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: @param aCity the city for which to find the time zone 070: @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: { 077: conn = DataSourceBean.getConnection();

79 078: Statement stat = conn.createStatement(); 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(result.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: @param aCity the city for which to find the time zone 097: @return the time zone or null if no match is found

80 098: */ 099: private static TimeZone getTimeZone(String city) 100: { 101: String[] ids = TimeZone.getAvailableIDs(); 102: for (int i = 0; i < ids.length; i++) 103: if (timeZoneIDmatch(ids[i], city)) 104: return TimeZone.getTimeZone(ids[i]); 105: return null; 106: } 107: 108: /** 109: Checks whether a time zone ID matches a city 110: @param id the time zone ID (e.g. "America/Los_Angeles") 111: @param aCity the city to match (e.g. "Los Angeles") 112: @return true if the ID and city match 113: */ 114: private static boolean timeZoneIDmatch(String id, String city) 115: { 116: String idCity = id.substring(id.indexOf('/') + 1); 117: return idCity.replace('_', ' ').equals(city);

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 o It carries out computations o 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 o Obtains the current time o Creates HTML document containing the information o 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; 03: import java.util.Date; 04: import javax.servlet.ServletException; 05: import javax.servlet.http.HttpServlet; 06: import javax.servlet.http.HttpServletRequest; 07: import javax.servlet.http.HttpServletResponse; 08: 09: /** 10: This servlet prints out the current date and time. 11: */ 12: public class DateServlet extends HttpServlet 13: { 14: public void doGet(HttpServletRequest request, 15: HttpServletResponse response) 16: throws ServletException, IOException 17: { 18: // get information 19: String now = new Date().toString();

88 20: 21: // set content type to HTML 22: response.setContentType("text/html"); 23: 24: // print formatted information 25: PrintWriter out = response.getWriter(); 26: 27: String title = "Date Servlet"; 28: out.println(" "); 29: out.println(title); 30: out.println(" "); 31: out.print(title); 32: out.println(" The current time is: "); 33: out.println(now); 34: out.println(" "); 35: 36: out.close(); 37: } 38: }

89 Servlets To deploy a servlet, you need to write a deployment descriptor The deployment descriptor gives the servlet a name The name may be different than the class name The deployment descriptor tells how to locate the servlet class The deployment descriptor tells which URL's map to the servlet

90 Servlets The deployment descriptor must be in the web.xml file The web.xml file goes in the WEB-INF subdirectory of the web application directory Put the class files into the classes subdirectory of the WEB-INF directory

91 Placement of Web Application Files

92 Servlets This second servlet lets the user supply a city name Use the request parameter of the doPost method to get the value Use the getParameter method of the request object

93 File zoneservlet.html 01: 02: 03: Time Zone Servlet Form 04: 05: 06: 07: City: 08: 09: 10: 11: 12: 13:

94 File TimeZoneServlet.Java 01: import java.io.PrintWriter; 02: import java.io.IOException; 03: import java.text.DateFormat; 04: import java.util.Date; 05: import java.util.TimeZone; 06: import javax.servlet.ServletException; 07: import javax.servlet.http.HttpServlet; 08: import javax.servlet.http.HttpServletRequest; 09: import javax.servlet.http.HttpServletResponse; 10: 11: /** 12: This servlet prints out the current local time. 13: The city name must be posted as value of the 14: "city" parameter. 15: */ 16: public class TimeZoneServlet extends HttpServlet 17: {

95 18: public void doPost(HttpServletRequest request, 19: HttpServletResponse response) 20: throws ServletException, IOException 21: { 22: // get information 23: 24: String cityName = request.getParameter("city"); 25: TimeZone zone = getTimeZone(cityName); 26: 27: // set content type to HTML 28: response.setContentType("text/html"); 29: 30: // print formatted information 31: PrintWriter out = response.getWriter(); 32: 33: String title = "Time Zone Servlet"; 34: out.println(" "); 35: out.println(title); 36: out.println(" "); 37: out.print(title);

96 38: out.println(" "); 39: 40: if (zone == null) 41: out.println("Sorry--unknown city"); 42: else 43: { 44: out.print("The current time in "); 45: out.print(cityName); 46: out.print(" is: "); 47: DateFormat formatter = DateFormat.getTimeInstance(); 48: formatter.setTimeZone(zone); 49: Date now = new Date(); 50: out.print(formatter.format(now)); 51: } 52: out.println(" "); 53: 54: out.close(); 55: } 56: 57: /**

97 58: Looks up the time zone for a city 59: @param aCity the city for which to find the time zone 60: @return the time zone or null if no match is found 61: */ 62: private static TimeZone getTimeZone(String city) 63: { 64: String[] ids = TimeZone.getAvailableIDs(); 65: for (int i = 0; i < ids.length; i++) 66: if (timeZoneIDmatch(ids[i], city)) 67: return TimeZone.getTimeZone(ids[i]); 68: return null; 69: } 70: 71: /** 72: Checks whether a time zone ID matches a city 73: @param id the time zone ID (e.g. "America/Los_Angeles") 74: @param aCity the city to match (e.g. "Los Angeles") 75: @return true if the ID and city match 76: */ 77: private static boolean timeZoneIDmatch(String id, String city)

98 78: { 79: String idCity = id.substring(id.indexOf('/') + 1); 80: return idCity.replace('_', ' ').equals(city); 81: } 82: }

99 Compilation of JSP Pages The JSP container translates the JSP pages into servlets This happens when the page is first requested Also whenever the page has changed Bean directives translate into Java code


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