1. JavaServer Pages (JSP)27
JavaServer Pages (JSP)

2. A fair request should be followed by the deed in silence.
If it’s a good script, I’ll do it and if it’s a bad script and they pay me enough, I’ll do it.
George Burns
A fair request should be followed by the deed in silence.
Dante Alighieri
Talent is a question of quantity. Talent does not write one page: it writes three hundred.
Jules Renard
Every action must be due to one or other of seven causes: chance, nature, compulsion, habit, reasoning, anger, or appetite.
Aristotle

3. OBJECTIVES In this chapter you will learn:
The differences between servlets and JSPs.
To create and deploy JavaServer Pages.
To use JSP’s implicit objects and scriptlets to create dynamic Web pages.
To specify global JSP information with directives.
To use actions to manipulate JavaBeans in a JSP, to include resources dynamically and to forward requests to other JSPs.

4. 27.1   Introduction
27.2   JavaServer Pages Overview
27.3   First JSP Example
27.4   Implicit Objects
27.5   Scripting
27.5.1  Scripting Components
27.5.2  Scripting Example
27.6   Standard Actions
27.6.1  <jsp:include> Action
27.6.2  <jsp:forward> Action
27.6.3  <jsp:useBean> Action
27.7   Directives
27.7.1  page Directive
27.7.2  include Directive
27.8   Case Study: Guest Book
27.9   Wrap-Up
27.10   Internet and Web Resources

5. 27.1 Introduction JavaServer Pages
Extension of Servlet technology
Separate the presentation from the business logic
Simplify the delivery of dynamic Web content
Reuse existing Java components
JavaBean
Custom-tag libraries
Encapsulate complex functionality
Classes and interfaces specific to JSP
Package javax.servlet.jsp
Package javax.servlet.jsp.tagext

6. 27.2 JavaServer Pages Overview
Key components
Directives
Actions
Scripting elements
Tag libraries

7. 27.2 JavaServer Pages Overview (Cont.)
Directive
Message to JSP container
i.e., program that compiles/executes JSPs
Enable programmers to specify
Page settings
Content to include from other resources
Custom tag libraries used in the JSP

8. 27.2 JavaServer Pages Overview (Cont.)
Action
Predefined JSP tags that encapsulate functionality
Often performed based on information from client request
Can be used to create Java objects for use in scriptlets

9. 27.2 JavaServer Pages Overview (Cont.)
Scripting elements
Enable programmers to insert Java code in JSPs
Performs request processing
Interacts with page elements and other components to implement dynamic pages
Scriptlets
One kind of scripting element
Contain code fragments
Describe the action to be performed in response to user request

10. 27.2 JavaServer Pages Overview (Cont.)
Custom Tag Library
JSP’s tag extension mechanism
Enables programmers to define new tags
Tags encapsulate complex functionality
Tags can manipulate JSP content

11. 27.2 JavaServer Pages Overview (Cont.)
JSPs
Look like standard XHTML or XML
Normally include XHTML or XML markup
Known as fixed-template data
Used when content is mostly fixed-template data
Small amounts of content generated dynamically
Servlets
Used when small amount of content is fixed-template data
Most content generated dynamically

12. Software Engineering Observation 27.1
Literal text in a JSP becomes string literals in the servlet that represents the translated JSP.

13. 27.2 JavaServer Pages Overview (Cont.)
When server receive the first JSP request
JSP container translates a JSP into a servlet
Handle the current and future requests
Code that represents the JSP
Placed in servlet’s _jspService method
JSP errors
Translation-time errors
Occur when JSPs are translated into servlets
Request-time errors
Occur during request processing
Methods jspInit and jspDestroy
Container invokes them when initializing and terminating a JSP
Defined in JSP declarations

14. Performance Tip 27.1
Some JSP containers translate JSPs to servlets at installation time. This eliminates the translation overhead for the first client that requests each JSP.

15. 27.3 First JSP Example Simple JSP example (Fig. 27.1) Demonstrates
Fixed-template data (XHTML markup)
Creating a Java object (java.util.Date)
Automatic conversion of JSP expression to a String
meta element to refresh Web page at specified interval
First invocation of clock.jsp
Notice the delay while:
JSP container translates the JSP into a servlet
JSP container compiles the servlet
JSP container executes the servlet
Subsequent invocations should not experience the same delay

16. meta element refreshes the Web page every 60 seconds
Outline
clock.jsp
(1 of 2)
Line 9
Line 24
meta element refreshes the Web page every 60 seconds
Creates Date object that is converted to a String implicitly and displayed in paragraph (p) element

17. Outline
clock.jsp
(2 of 2)
Program output

18. Software Engineering Observation 27.2
JavaServer Pages are easier to implement than servlets when the response to a client request consists primarily of markup that remains constant between requests.

19. Software Engineering Observation 27.3
The JSP container converts the result of every JSP expression into a string that is output as part of the response to the client.

20. 27.4 Implicit Objects Implicit Objects
Provide access to many servlet capabilities within a JSP
Four scopes
Application scope
Objects owned by the container application
Any servlet or JSP can manipulate these objects
Page scope
Objects that exist only in page in which they are defined
Each page has its own instance of these objects

21. 27.4 Implicit Objects (Cont.)
Request scope
Objects exist for duration of client request
Objects go out of scope when response sent to client
Session scope
Objects exist for duration of client’s browsing session
Objects go out of scope when client terminates session or when session timeout occurs

22. Fig. 27.2 | JSP implicit objects. (1 of 2)

23. Fig. 27.2 | JSP implicit objects. (2 of 2)

24. 27.5 Scripting Scripting Dynamically generated content
Insert Java code and logic in JSP using scripting

25. 27.5.1 Scripting Components JSP scripting components
Scriptlets (delimited by <% and %>)
Comments
JSP comments (delimited by <%-- and --%>)
XHTML comments (delimited by <!-- and -->)
Java’s comments (delimited by // and /* and */)
Expressions (delimited by <%= and %>)
Declarations (delimited by <%! and %>)
Escape sequences

26. Common Programming Error 27.1
Placing a JSP comment or XHTML comment inside a scriptlet is a translation-time syntax error that prevents the JSP from being translated properly.

27. Software Engineering Observation 27.4
JSPs should not store client state information in instance variables. Rather, they should use the JSP implicit session object. For more information on how to use the session object, visit Sun’s J2EE tutorial at java.sun.com/j2ee/1.4/docs/tutorial/doc/index.html.

28. Fig. 27.3 | JSP escape sequences.

29. 27.5.2 Scripting Example Demonstrate basic scripting capabilities
Responding to get requests

30. Software Engineering Observation 27.5
Scriptlets, expressions and fixed-template data can be intermixed in a JSP to create different responses based on the information in a request.

31. Outline (1 of 3) Lines 17-23 Line 19 Line 26
welcome.jsp
(1 of 3)
Lines 17-23
Line 19
Line 26
Scriptlet used to insert Java code
Use request implicit object to get parameter
JSP expression

32. Scriptlets used to insert Java code
Outline
welcome.jsp
(2 of 3)
Lines and lines 45-49

33. Outline
welcome.jsp
(3 of 3)
Program output

34. Error-Prevention Tip 27.1
It is sometimes difficult to debug errors in a JSP, because the line numbers reported by a JSP container normally refer to the servlet that represents the translated JSP, not the original JSP line numbers. Program development environments enable JSPs to be compiled in the environment, so you can see syntax error messages. These messages include the statement in the servlet that represents the translated JSP, which can be helpful in determining the error.

35. Error-Prevention Tip 27.2
Many JSP containers store the source code for the servlets that represent the translated JSPs. For example, the Tomcat installation directory contains a subdirectory called work in which you can find the source code for the servlets translated by Tomcat. Recall from Chapter 26 that the log files located in the logs subdirectory of the Tomcat installation directory are also helpful for determining the errors.

36. Error-Prevention Tip 27.3
Always put the closing brace for the if statement and the else in the same scriptlet.

37. 27.6 Standard Actions JSP standard actions
Provide access to common tasks performed in a JSP
Including content from other resources
Forwarding requests to other resources
Interacting with JavaBeans
JSP containers process actions at request time
Delimited by <jsp:action> and </jsp:action>

38. Fig. 27.5 | JSP standard actions. (1 of 2)

39. Fig. 27.5 | JSP standard actions. (2 of 2)

40. 27.6.1 <jsp:include> Action
Enables dynamic content to be included in a JSP
More flexible than include directive
Requires more overhead when page contents change frequently

41. Software Engineering Observation 27.6
According to the JavaServer Pages 2.0 specification, a JSP container is allowed to determine whether a resource included with the include directive has changed. If so, the container can recompile the JSP that included the resource. However, the specification does not provide a mechanism to indicate a change in an included resource to the container.

42. Performance Tip 27.2
The <jsp:include> action is more flexible than the include directive, but requires more overhead when page contents change frequently. Use the <jsp:include> action only when dynamic content is necessary.

43. Common Programming Error 27.2
Specifying in a <jsp:include> action a page that is not part of the same Web application is a request-time error—the <jsp:include> action will not include any content.

44. Fig. 27.6 | Action <jsp:include> attributes.

45. Outline
include.jsp
(1 of 3)

46. Outline (2 of 3) Lines 38-39 Line 45
include.jsp
(2 of 3)
Lines 38-39
Line 45
Lines 49-50
Use JSP include action to include banner.html
Use JSP include action to include toc.html
Use JSP include action to include clock2.jsp

47. Outline
include.jsp
(3 of 3)
Program output

48. Outline
banner.html

49. Outline
toc.html

50. Outline
clock2.jsp
Line 14
Lines 17-20
Line 25
Use request object’s getLocale method to obtain the client’s Locale
Invoke DateFormat static method getDateTimeInstance to obtain a DataFormat object for the specified Locale
Format Date with specified DataFormat

51. 27.6.2 <jsp:forward> Action
Enables JSP to forward request to different resources
Forward requests to resources in same context
<jsp:param> action
Specifies name-value pairs of information
Name-value pairs are passed to other actions

52. Software Engineering Observation 27.7
When using the <jsp:forward> action, the resource to which the request will be forwarded must be in the same context (Web application) as the JSP that originally received the request.

53. Outline (1 of 2) Line 14 Lines 20-23
forward1.jsp
(1 of 2)
Line 14
Lines 20-23
Use request implicit object to get parameter
Forward request to forward2.jsp

54. Outline
forward1.jsp
(2 of 2)
Program output

55. Get date parameter from request
Outline
forward2.jsp
(1 of 2)
Line 21
Line 28
Receive request from forward1.jsp, then get firstName parameter from request
Get date parameter from request

56. Outline
forward2.jsp
(2 of 2)
Program output

57. 27.6.3 <jsp:useBean> Action
Enables JSP to manipulate Java object
Creates Java object or locates an existing object for use in JSP

58. Common Programming Error 27.3
One or both of the <jsp:useBean> attributes class and type must be specified—otherwise, a translation-time error occurs.

59. Fig. 27.13 | Attributes of the <jsp:useBean> action.

60. Return image file name for book cover image
Outline
Rotator.java
(1 of 2)
Lines 26-29
Return image file name for book cover image

61. Return hyperlink to book at Amazon.com
Outline
Rotator.java
(2 of 2)
Lines 32-35
Lines 39-42
Update Rotator so subsequent calls to getImage and getLink return information for different advertisements

62. Outline Use jsp:useBean action to obtain reference to Rotator object
adrotator.jsp
(1 of 2)
Lines 7-8
Line 19
Lines 24-29
Invoke Rotator’s nextAd method
Define hyperlink to Amazon.com site

63. Outline
adrotator.jsp
(2 of 2)
Program output

64. 27.6.3 <jsp:useBean> Action (Cont.)
Action <jsp:getProperty>
Attribute name
Specify the bean object to manipulate
Attribute property
Specify the property to get
Replace <jsp:getProperty> action with JSP expressions
<%= rotator.getLink() %>
<%= rotator.getImage() %>

65. Software Engineering Observation 27.8
Action <jsp:setProperty> can use request-parameter values to set JavaBean properties of the following types: Strings, primitive types (boolean, byte, char, short, int, long, float and double) and type-wrapper classes (Boolean, Byte, Character, Short, Integer, Long, Float and Double). See Fig. 27.22 for an example.

66. Fig. 27.16 | Attributes of the <jsp:setProperty> action.

67. Common Programming Error 27.4
Conversion errors occur if you use action <jsp:setProperty>’s value attribute to set JavaBean property types that cannot be set with request parameters.

68. 27.7 Directives JSP directives Messages to JSP container
Enable programmer to:
Specify page settings
Include content from other resources
Specify custom-tag libraries
Delimited by and %>

69. Fig | JSP directives.

70. 27.7.1 page Directive JSP page directive
Specifies JSP’s global settings in JSP container

71. Common Programming Error 27.5
Providing multiple page directives with one or more repeated attributes in common is a JSP translation-time error, unless the values for all repeated attributes are identical. Also, providing a page directive with an attribute or value that is not recognized is a JSP translation-time error.

72. Software Engineering Observation 27.9
According to the JSP specification, section , the extends attribute “should not be used without careful consideration as it restricts the ability of the JSP container to provide specialized superclasses that may improve on the quality of rendered service.” Remember that a Java class can extend exactly one other class. If your JSP specifies an explicit superclass, the JSP container cannot translate your JSP into a subclass of one of the container application’s own enhanced servlet classes.

73. Fig. 27.18 | Attributes of the page directive. (1 or 3)

74. Fig. 27.18 | Attributes of the page directive. (2 or 3)

75. Fig. 27.18 | Attributes of the page directive. (3 or 3)

76. Common Programming Error 27.6
Using JSP implicit object session in a JSP that does not have its page directive attribute session set to true is a translation-time error.

77. 27.7.2 include Directive JSP include directive
Includes content of another resource at JSP translation time
Not as flexible as <jsp:include> action

78. Outline
includeDirective.j sp
(1 of 3)

79. Outline (2 of 3) Line 34 Use include directive to include banner.html
includeDirective.j sp
(2 of 3)
Line 34
Line 40
Line 44
Use include directive to include banner.html
Use include directive to include toc.html
Use include directive to include clock2.jsp

80. Outline
includeDirective.j sp
(3 of 3)
Program output

81. 27.8 Case Study: Guest Book Demonstrate Action <jsp:setProperty>
JSP page directive
JSP error pages
Use of JDBC

82. Outline
GuestBean.java
(1 of 2)
Lines 7-9
GuestBean declares three guest properties: firstName, lastName and

83. Outline
GuestBean.java
(2 of 2)

84. Outline (1 of 3) Line 19 Line 22 Line 23 Line 24 Line 25
GuestDataBean.java
(1 of 3)
Line 19
Line 22
Line 23
Line 24
Line 25
Load MySQL driver
Create a CachedRowSet object using Sun’s reference implementation CachedRowSetImpl
Set the CachedRowSet’s database URL property
Set the CachedRowSet’s database username property
Set the CachedRowSet’s database password property

85. Outline Set the CachedRowSet’s database command property
Execute the query specified by the command property
GuestDataBean.java
(2 of 3)
Lines 28-29
Line 30
Line 38
Lines 41-50
Move the CachedRowSet’s cursor before the first row
Create the GuestBean objects for each row in the CachedRowSet

86. Outline
Invoke the CachedRowSet’s moveToInsertRow method to remember the current row and move the cursor to the insert row
GuestDataBean.java
(3 of 3)
Line 58
Lines 61-63
Line 64
Line 65
Line 66
Invoke the CachedRowSet’s updateString method to update the column values
Invoke the CachedRowSet’s insertRow method to insert the row into the rowset
Invoke the CachedRowSet’s moveToCurrentRow method to move the cursor back to the current row
Invoke the CachedRowSet’s acceptChanges method to propagates the changes in the rowset to the underlying database

87. page directive defines information that is globally available in JSP
Outline
page directive defines information that is globally available in JSP
guestBookLogin.jsp
(1 of 3)
Line 8
Lines 11-14
Use jsp:useBean actions to obtain references to GuestBean and GuestDataBean objects

88. Set properties of GuestBean with request parameter values, because the input elements have the same names as the GuestBean properties
Outline
Verify that the user fills in all the entries, including first name, last name and
guestBookLogin.jsp
(2 of 3)
Line 34
Lines 36-89

89. Outline
guestBookLogin.jsp
(3 of 3)
Line 74
Line 77
Add GuestBean guest to GuestDataBean guestData
Forward request to guestBookView.jsp

90. 27.8 Case Study: Guest Book (Cont.)
Line 34
Specify “*” for attribute property
Match request parameters to properties
Can set the properties individually
<jsp:setProperty name = “guest” property = “firstName” param = “firstName” />
<jsp:setProperty name = “guest” property = “lastName” param = “lastName” />
<jsp:setProperty name = “guest” property = “ ” param = “ ” />
<% guest.setFirstName( request.getParameter( “firstName” ) ); %>

91. Use jsp:useBean action to obtain reference to GuestDataBean
Outline
Use page directive import to specify Java classes and packages that are used in JSP context
guestBookView.jsp
(1 of 2)
Lines 9 and 10
Lines 13-14
Use jsp:useBean action to obtain reference to GuestDataBean

92. Outline
guestBookView.jsp
(2 of 2)
Lines 45-64
Use scriptlet and expressions to display last name, first name and address for all guests

93. Outline
Use page directive isErrorPage to specify that guestBookError-Page is an error page
guestBookErrorPage .jsp
(1 of 3)
Line 8

94. Use implicit object exception to determine error to be displayed
Outline
Use implicit object exception to determine error to be displayed
guestBookErrorPage .jsp
(2 of 3)
Lines 28 and 36

95. Display the actual error message from the exception
Outline
guestBookErrorPage .jsp
(3 of 3)
Line 60
Display the actual error message from the exception

96. Fig. 27.25 | JSP guest book sample output windows. (1 of 3)

97. Fig. 27.25 | JSP guest book sample output windows. (2 of 3)

98. Fig. 27.25 | JSP guest book sample output windows. (2 of 3)