jsp

1
Chapter 10

• jsp

2
Purpose

• Simplifies the delivery of dynamic Web content,
  using predefined components and server-side
  scripting
• javax.servlet.jsp, javax.servlet.jsp.tagext
  provide functionality

3
JSP
Template data static can be sent directly
to client
Elements dynamic interpreted by container
JSP normally includes XHTML or XML markup.  Such
markup is known as fixed-template data or
fixed-template text.  JSP is typically used when
most of the content sent to the client is
fixed-template data and only a small portion is
generated dynamically with Java code.  Servlets
are typically used when only a small portion of
the content is fixed-template data.  Some
servlets just perform a task for the client, then
invoke other servlets or JSPs to provide a
response. In most cases, servlet and JSP
technologies are interchangeable.  JSPs normally
execute as part of a Web server. The server (or
Tomcat) is the JSP container.
4
Dynamic JSP Components

• actions encapsulate functionality in predefined
  tags. Can create Java objects for use in
  scriptlets (aka scripting elements).
• scriptlets insert Java code into html.
  interacts with components in a JSP to process
  requests.
• directives messages to the JSP container that
  enable the programmer to specify page settings,
  include content from other resources, specify
  custom tag libraries etc.
• tag libraries tag extension mechanism that
  enables programmers to create custom tags.  These
  tags enable programmers to manipulate JSP
  content. 

5
JSP Lifecycle
browser
request
Translate to servlet
yes
First Time?
Tomcat
no
find in work directory
jsp service method ready for client

• If there are any errors compiling the new
  servlet, they result in translation-time errors. 
  
• Any errors during request processing are
  request-time errors.
• Some JSP containers translate JSP at
  installation time, to eliminate overhead for
  first client.

6
Expressions

• lt gt
• Send a string of text to client
• Object left as result of evaluation will have
  toString() called

7
clock.jsp uses expression for Date

• lt?xml version "1.0"?gt
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN"
• "http//www.w3.org/TR/xhtml1/DTD/xhtml1-strict.
  dtd"gt
• lthtml xmlns http//www.w3.org/1999/xhtmlgt
• ltheadgt
• ltmeta http-equiv "refresh" content "60"
  /gt
• lttitlegtA Simple JSP Examplelt/titlegt
• ltstyle type "text/css"gt
• .big font-family helvetica, arial,
  sans-serif
• font-weight bold
• font-size 2em
• lt/stylegt
• lt/headgt
• ltbodygt
• ltp class "big"gtSimple JSP Examplelt/pgt
• lttable style "border 6px outset"gt

8
Scripting

• In some cases, the content of generated XHTML
  documents is static, but is output only if
  certain conditions are met (e.g., providing
  values in a form that submits a request). 
• Scripting provides ability to use Java code, but
  no class declaration
• Allows for loops, conditions
• JSP currently supports scripting only with Java. 
  Future JSP versions may support other scripting
  languages.

9
Scripting Components

• Scriptlets are blocks of code delimited by lt and
  gt.  They contain Java statements that the
  container places in method _jspService at
  translation time.
• Scriptlets, expressions and fixed template data
  can be intermixed in a JSP to create different
  responses.
• JSPs can be difficult to debug, because line
  numbers reported in JSP container refer to
  translated JSP servlet, not the original JSP line
  numbers.  Some IDEs allow JSPs to be compiled in
  the environment, so you can see syntax error
  messages
• The Tomcat installation directory contains a
  subdirectory called work where you can find
  source code for the translated servlets.

10
Comments

• JSP comments are delimited by lt-- and --gt.  Can
  be placed throughout a JSP, but not inside
  scriptlets.
• XHTML comments are delimited with lt!-- and --gt. 
  Can be placed throught JSP, but not inside
  scriptlets. 
• Scriptlets can use Java comments (delimited by //
  or /  and /).

11
Declarations

• Declarations are delimited by lt! and gt
• They enable a JSP programmer to define variables
  and methods.  Variables and methods are instance
  members of the servlet class that represents the
  translated JSP.  Declarations use Java syntax
  (e.g., must end in a semicolon).   lt! int
  counter 0 gt
• Variables and methods in JSP declarations are
  initialized when JSP is initialized and are
  available in all scriptlets and expressions in
  the JSP. 
• JSPs should not store client state information in
  instance variables.  Should use JSP implicit
  session object.
• Not thread-safe unless programmer takes care of

12
Escape Sequences

• Must use escape sequences for characters used as
  JSP delimiters. 
• lt  -gt lt\
• gt -gt \gt
• ' -gt \'
• " -gt \"
• \ -gt \\

13
Implicit Objects

• Because no method calls, have automatic objects
  available
• response httpServletResponse
• request - httpServletRequest
• out response.getWriter
• page this reference in servlet

14
clock2.jsp - script

• lttablegt
• lttrgt
• lttd style "background-color black"gt
• ltp class "big" style "color cyan
  font-size 3em
• font-weight bold"gt
• lt-- script to determine client
  locale and format date accordingly --gt
• lt
• // get client locale
• java.util.Locale locale
  request.getLocale()
• // get DateFormat for client's
  Locale
• java.text.DateFormat dateFormat
• java.text.DateFormat.getDateTime
  Instance(
• java.text.DateFormat.LONG,
  java.text.DateFormat.LONG, locale )
• gt lt-- end script --gt
• lt-- output date --gt
• lt dateFormat.format( new
  java.util.Date() ) gt
• lt/pgt
• lt/tdgt

15
welcome.jsp - scriptlet

• ltbodygt
• lt // begin scriptlet
• String name request.getParameter(
  "firstName" )
• if ( name ! null )
• gt lt-- end scriptlet to insert fixed
  template data --gt
• lth1gt
• Hello lt name gt, ltbr /gt
• Welcome to JavaServer Pages!
• lt/h1gt
• lt // continue scriptlet
• // end if
• else
• gt lt-- end scriptlet to insert fixed
  template data --gt
• ltform action "welcome.jsp" method
  "get"gt
• ltpgt Type your first name and press
  Submitlt/pgt
• ltpgtltinput type "text" name
  "firstName" /gt
• ltinput type "submit" value
  "Submit" /gt
• lt/pgt
• lt/formgt

16
Exercise

• Run jsp examples clock.jsp, clock2.jsp,
  welcome.jsp
• Look at work directory, see servlets
• Change clock.jsp to display another expression,
  possibly the result of a numeric calculation
• Change clock2.jsp to have a different date format
• Change welcome.jsp to accept a different field
  and display a different message

17
Standard Actions

• Actions provide JSP implementors with access to
  common tasks performed in a JSP. 
• Actions are delimited by ltjspactiongt and
  lt/jspactiongt where action is the standard action
  name.
• Can use lt/action /gt if nothing appears between
  start/end tags.
• ltjspincludegt - dynamically includes another
  resource in a JSP. 
• ltjspforwardgt - forwards to JSP, servlet or
  static page.  Terminates current JSP's execution.
  
• ltjspplugingt - Allows plug-in component to be
  added to a page in the form of a browser-specific
  object or embed HTML element.  Can be an applet,
  which enables downloading the Java Plug-in, if
  not already installed.
• ltjspparamgt - Used with include, forward and
  plugin actions to specify additional name/value
  pairs of information.

18
Standard Actions, cont

• ltjspuseBeangt - specifies that JSP use a JavaBean
  instance.  Specifies the scope of the bean and
  assigns it an ID that scripting components can
  use to manipulate the bean.
• ltjspsetPropertygt - sets a property in the
  specified JavaBean.  Matches request parameters
  to bean properties of the same name.
• ltjspgetPropertygt - gets a property in the
  specified JavaBean, converts the result to a
  string for output in the response.

19
Include Mechanism

• JSP supports two include mechanisms
• The include directive (covered later) copies the
  content into the JSP once, at translation time. 
  
• ltjspincludegt enables dynamic content to be
  included.  If the included resource changes
  between requests, the next request includes the
  new content.   This is more flexible than the
  include directive, but requires more overhead. 
  Use only when necessary. Includes attributes
• page- specifies the relative URL of the resource
  to include.  Must be part of the same Web
  application, or a request-time error occurs.
• flush- specifies whether buffer should be flushed
  after include is performed.  In JSP 1.1, required
  to be true. If this attribute is not specified, a
  translation-time error occurs.

20
Include.jsp

• ltbodygt
• lttablegt
• lttrgt
• lttd style "width 160px
  text-align center"gt
• ltimg src "images/logotiny.png"
• width "140" height "93"
• alt "Deitel Associates,
  Inc. Logo" /gt
• lt/tdgt
• lttdgt
• lt-- include banner.html in this
  JSP --gt
• ltjspinclude page "banner.html"
  flush "true" /gt
• lt/tdgtlt/trgt
• lttrgt
• lttd style "width 160px"gt
  
• lt-- include toc.html in this JSP
  --gt
• ltjspinclude page "toc.html"
  flush "true" /gt
• lt/tdgt
• lttd style "vertical-align top"gt
• lt-- include clock2.jsp in this
  JSP --gt

21
forward1.jsp

• ltbodygt
• lt // begin scriptlet
• String name request.getParameter(
  "firstName" )
• if ( name ! null )
• gt lt-- end scriptlet to insert fixed template
  data --gt
• ltjspforward page "forward2.jsp"gt
• ltjspparam name "date"
• value "lt new java.util.Date()
  gt" /gt
• lt/jspforwardgt
• lt // continue scriptlet
• // end if
• else
• gt lt-- end scriptlet to insert fixed template
  data --gt
• ltform action "forward1.jsp" method
  "get"gt
• ltpgtType your first name and press
  Submitlt/pgt
• ltpgtltinput type "text" name
  "firstName" /gt
• ltinput type "submit" value
  "Submit" /gt
• lt/pgt
• lt/formgt

22
forward2.jsp

• ltbodygt
• ltp class "big"gt
• Hello lt request.getParameter( "firstName"
  ) gt, ltbr /gt
• Your request was received ltbr /gt and
  forwarded at
• lt/pgt
• lttable style "border 6px outset"gt
• lttrgt
• lttd style "background-color black"gt
• ltp class "big" style "color
  cyan"gt
• lt request.getParameter( "date" )
  gt
• lt/pgt
• lt/tdgt
• lt/trgt
• lt/tablegt
• lt/bodygt

23
Exercise

• Modify include to have different layout/ pages
  included
• Modify forward1 and forward2 to accept a
  different piece of information and respond
  differently
• Also experiment with if-else structure

24
Plugins

• type - Component type bean or applet
• code - class that represents the component
• codebase - location of class specified in the
  code attribute and archives specified with
  archive attribute
• align - alignment of the component
• archive  - space-separated list of archive files
  that contain resources used by the component. 
  May include the class specified by the code
  attribute.
• height - component height specifed in pixels or
  percentage
• hspace- number of pixels of space that appear to
  the left and to the right of the component.
• jreversion - version of Java Runtime Environment
  and plug-in required to execute component. 
  Default is 1.1.
• name - name of component.
• vspace- number of pixels of space that appear
  above and below the component.
• title - text that describes the component.
• width  - component width specified in pixels or
  percentage.
• nspluginur1- location for download of Java
  Plug-in for Netscape
• iepluginurl - location for download of Java
  Plug-in for Internet Explorer
• Most Web browsers do not support applets written
  for Java 2 platform, so you must use Java
  Plug-in.  (still true?)

25
useBean Action

• like constructor, only executed when bean is
  first created
• has attributes that can be manipulated
• id - name used to manipulate the Java object with
  actions like ltjspsetPropertygt and
  ltjspgetPropertygt A variable of this name is
  available for use in scripting elements. The bean
  should name properties using set and get in order
  to work with setProperty and getProperty.
• scope- Can have page, request, session or
  application scope that indicates where they can
  be used in a Web application.
• class - fully qualified class name of the Java
  object
• beanName - name of a bean that can be used with
  method instantiate of class java.beans.Beans to
  load a JavaBean
• type- Can be the same as the class attribute, a
  superclass of that type or an interface
  implemented by that type.  A ClassCastException
  occurs if the Java object is not of the type
  specified with the attribute type.
• One or both of type and class must be specified,
  or a translation-time error occurs

26
setProperty

• can be used to set JavaBean properties
• Often used to map request parameter values to
  JavaBean properties
• Can set primitive types boolean, byte, char, int,
  long, float, double and java.lang types String,
  Boolean, Byte, Character, Integer, Long, Float
  and Double.
• Attributes used with setProperty
• name- ID of JavaBean
• property - name of property to set.  Can specify
  '' to cause JSP to match the request parameters
  to the properties of the bean.  If the value of
  the request parameter is "", property remains
  unchanged.
• param- Can be used to specify which request
  parameter to use, in case names do not match bean
  properties. If omitted, names must match.
• value - value to assign.  Often the result of a
  JSP expression.  Used when property types cannot
  be set with request parameters (avoid conversion
  errors).

27
adRotator.jsp

• ltjspuseBean id "rotator" scope "session"
• class "com.deitel.advjhtp1.jsp.beans.Rotator"
  /gt
• lthtml xmlns "http//www.w3.org/1999/xhtml"gt
• ltheadgt
• lttitlegtLogoAnimator Examplelt/titlegt
• ltstyle type "text/css"gt
• .big font-family helvetica, arial,
  sans-serif
• font-weight bold
• font-size 2em
• lt/stylegt
• lt-- update advertisement --gt
• lt rotator.nextAd() gt
• lt/headgt
• ltbodygt
• ltp class "big"gtAdRotator Examplelt/pgt ltpgt
• lta href "ltjspgetProperty name
  "rotator" property "link" /gt"gt
• ltimg src "ltjspgetProperty name
  "rotator" property "image" /gt"

28
Exercise

• Run adRotator.jsp
• Create your own small bean, attach it to a jsp.
• Example User.java. I have a user name and
  message. The output message depends on the user
  name. (idea business login encapsulated in the
  java class. Want to eliminate scriptlets
  expressions by using beans, makes cleaner syntax
  for jsp)

29
Directives

• Messages to JSP that enable you to specify page
  settings, to include content from other
  resources, and to specify custom-tag libraries. 
  Directives are processed at translation time
  (i.e., before any requests are received). 
• Three types of directives page, include and
  taglib

30
Handling Exceptions

• When a JSP performs an operation that causes an
  exception, the JSP can include scriptlets that
  catch the exception and process it. 
• Exceptions that are not caught can be forwarded
  to a JSP error page.
• page directive defines information that is
  globally available in a JSP
• Directives are delimited by lt_at_ and gt
• errorPage attribute specifies page to handle all
  uncaught exceptions
• isErrorPage set to true creates a page that can
  be used to catch errors
• the implicit object exception can only be used in
  error pages

31
Page Directives

• Attributes include
• language - scripting language used, currently
  must be java
• extends - class from which JSP will be inherited,
  must be fully qualified
• import - comma-separated list of fully qualified
  names/packages to be used.
• session - specifies whether the page participates
  in a session.  Default is true, which makes the
  implicit object session available. 
• buffer - size of output buffer used with implicit
  object out.  Can be none or a value such as 8kb
  (the default).
• autoFlush - If true (the default), indicates
  buffer associated with out should be flushed
  automatically when full.  If false, an exception
  occurs when the buffer is full. 
• isThreadSafe - If true (default), the page can
  process multiple requests at the same time.  JSP
  allows multiple instances of a JSP if not thread
  safe.
• info- information string that describes the
  page.  Returned by getServletInfo method.
• errorPage - processes exceptions.
• isErrorPage - if true, will handle exceptions.
• contentType - MIME type of data in response,
  default is text/html.

32
On Your Own

• Review Guest Book application
• Interacts with database
• Uses GuestDataBean
• Uses one error page for application
  (guestBookErrorPage.jsp)

33
Include directives

• includes the content of another resource, at
  compile time.  Only attribute is a file that
  specifies the URL of the page to include. 
  ltjspincludegt is processed each request to the
  server, so should be used if content of included
  resource can change.
• view includeDirective.jsp

34
JSP

• JSP syntax may be normal, as in text examples
• Newer versions are XML-compliant
• Not widely supported in 2003, probably is now
• Easier to use with development tools