Using JavaServer Pages

1
Using JavaServer Pages

• Harry R. Erwin, PhD
• CIT304/CSE301

2
Review

• Last lecture, we examined the use of Java
  servlets as a way to provide dynamic content.
• Problems
• Requires fully-qualified Java programmers ()
• Tedious and error-prone ()
• Time-consuming and requires frequent update ()
• Adding a new servlet involves editing XML and
  restarting the application ()
• Mixing static HTML with servlets does not scale
  ().
• This lecture, we will examine the use of
  JavaServer Pages to overcome these problems.

3
Resources

• Farley, Crawford, and Flanagan, 2002, Java
  Enterprise in a Nutshell, second edition,
  OReilly, ISBN 0-596-00152-5. For programmers.
• Bergsten, 2002, JavaServer Pages, second edition,
  OReilly, ISBN 0-596-00317-X. Covers JSP 1.2,
  for both programmers and web page authors. Has
  lots of worked examples. Recommended. If you have
  to manage web application development, it wont
  hurt you to know something about the process.

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JavaServer Pages (JSP)

• Allow you to embed the dynamic elements into the
  static content.
• Can be edited using a text editor or HTML
  authoring tool.
• Can be previewed live in the various browsers
  that you plan to support.

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Template Engines
Resources
Template Processor
Web Server
Web Browser
Instruction Template
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Java and JSP

• JSP pages are compiled into Java servlets before
  being executed.
• Benefits
• More efficient lifecycle
• Integration with Java
• Easy use of JavaBeans without writing code
• Java code can be completely avoided.
• Avoids programming.

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JSP Basics

• Individual JSP pages are text files stored on the
  web server.
• When a page is first requested, the JSP engine
  uses the page to generate a servlet.
• The compiled servlet is saved and used to handle
  later requests.
• When a page is modified, the servlet is
  recreated.
• Precompilation of pages is also feasible.

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A Simple JSP (from Java Enterprise in a Nutshell)
ltHTMLgt ltBODYgt Hello, sailor, it is now lt new
java.util.Date().toString() gt lt/BODYgt lt/HTMLgt
The only non-self-evident element is the
new java.util.Date().toString() This
creates a date object and converts it to a String
that can be displayed. The lt gt tag is are used
to display a Java variable. XML syntax can also
be used, if you want to be open to the future.
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Points to Note

• More generally, the lt gt elements (HTML/XML
  comments) can be used to insert regular Java code
  to control the flow of a page.
• We will discuss this in more detail next lecture.
• The next slide gives an example of an if, then,
  else flow control construct used in a JSP page.
  This is also from Java Enterprise in a Nutshell.

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Java Flow Control
ltHTMLgt ltBODYgt lt java.util.Date theDate new
java.util.Date() gt lt int theHour
theDate.getHours() gt lt if(theHourlt12) gt
Good morning, lt else gt Good
afternoon, lt gt sailor. It is now lt
theDate.toString() gt. lt/BODYgt lt/HTMLgt
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Java APIs Available

• JDBC (ODBC)
• RMI and CORBA
• Java Naming and Directory Interface
• Enterprise JavaBeans
• Java Message Service
• Java Transaction API
• JAXP
• JavaMail

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JSP Directives

• Affect the entire page.
• Begin with lt_at_ or lt _at_
• lt _at_include filedata.htmlgt
• Used to include static content
• lt _at_page gt
• Used to set page parameters
• lt _at_taglib gt
• Declares a tag library (later)

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Important Page Directives

• contentType
• MIME type of the page, default text/html
• extends
• JspPage class to be used if not default.
• import
• Java classes or packages to import.
• info
• A description of JSP page.
• session
• Indicates whether page participates in a user
  session.

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Declaration Elements

• This is another type of tag used to create
  variables.
• lt! global variable declarationvalue gt
• These are defined at the level of the JSP rather
  than at the session level. They persist across
  invocations.
• They can be used to count hits and detect
  hacking. Not all that useful. Use other
  approaches, if the data need to persist whenever
  the JSP is rebuilt and reloaded.

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Built-ins

• Your web server provides classes that the JSP can
  use. These include
• Configuration data
• The standard output stream
• The request that created the invocation
• The response being generated
• The current users session record.

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Whats in it for the Web Designer?

• JSP supports action tags.
• These are regular HTML tags of two types
• Built-in functions
• Custom tags
• Built-in functions use XML namespace-enabled tag
  syntax. They work with JavaBeans, too.

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Standard Action Tags

• ltjspuseBeangt imports a JavaBeans component.
• ltjspgetPropertygt gets a property value and adds
  it to the response.
• ltjspsetPropertygt sets a property value.
• ltjspincludegt includes the response from a
  servlet or JSP page that is called for the
  request.
• ltjspforwardgt forwards the call to a servlet or
  JSP page for service.
• ltjspparamgt adds a parameter to a request.
• ltjspplugingt generates the OBJECT or EMBED tag
  for an applet.

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taglib Directives

• If the web site architect wants to extend the JSP
  tag syntax, she can also define custom action
  tags. These are organized into Tag Libraries and
  can be loaded using the taglib directive.
• This allows her to remove almost all Java code
  from the JSPs. Her web page developers use these
  custom tags to replace the calls to Java
  functions, beans and programs.
• The programmers can then do their jobs separately
  from everyone else.

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Conclusions

• JSP is a solution to providing dynamic content.
• Equivalent to ASP.NET but currently more popular.
• Can be used to avoid Java scripting.
• Next lecture
• Java programming basicsjust enough to let you
  organize your JSP pagesthere is no requirement
  to learn class or method syntax unless you want
  to provide programming support to a web design
  organization.