Introduction to Java Server Pages technology by Naomi Chen

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Introduction to Java Server Pages technologyby
Naomi Chen
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What is JSP?

• Java based technology that simplifies the
  developing of dynamic web sites
• JSP pages are HTML pages with embedded code that
  allows to access data from Java code running on
  the server
• JSP provides separation of HTML presentation
  logic from the application logic.

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JSP Flow
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Comparison with existing technologies CGI

• CGI(Common Gateway Interface) programs (typically
  written in C or Perl) interact with the user by
  reading the user's input, HTML forms, and
  returning custom HTML pages.
• Problems
• For each user request the CGI script must be
  loaded, run, and unloaded.
• Designed to handle only a single request needed
  additional session support (to remember a users
  state between requests for a example).
• JSP vs. CGI
• JSP can maintain state on the server between
  requests
• Spawns a new thread for each request
• Does not have to be loaded each time, once it has
  been initialized
• Runs in a ready-loaded JVM as an extension to the
  web server.

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Comparison with existing technologies ASP

• ASP (Active Server Pages) from Microsoft is the
  main competing technology for JSP.
• JSP ASP are similar in the way they support the
  creation of dynamic web pages, using HTML
  templates, scripting code and components for
  business logic.

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Comparison with existing technologies ASP
(continue)

• ASP used on Microsoft IIS pr PWS web servers. Two
  third parties, Chili!Soft and Halcyonsoft sell
  software that allows ASPs to be uses with other
  platforms the main problem is in porting the COM
  components to the new platform.
• JSPs score over ASP
• JSPs are interprted only once, to Java byte-code,
  and re-interpreted only when the file is modified
• JSPs run on all the main web servers
• JSPs provide better facilities for separation of
  page code and template data by means of
  JavaBeans, Enterprise JavaBeans and custom tag
  libraries.
• For more information see Sun JSP vs. ASP page

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Comparison with existing technologies Servlets

• Servlets are standard, server-side Java
  applications that extend the capabilities of a
  Web server.
• Java Servlets programming model is similar to CGI
  scripts.
• Servlets run inside a single process associated
  with a web server.
• Instead of creating a process for each request
  (as CGI) JVM cerates a Java thread to handle each
  servlet request.
• JVM persists beyond the life of a single request
  (so requests can share data and resources).
• Essence Java code that outputs the HTML
  (out.println approach).
• All benefits of the core Java platform OOP
  model, cross-platform, memory management, rich
  collections of Java APIs., etc.
• Problems
• All document contents, both static and dynamic,
  reside in program source code.

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JSP Technology

• JSP technology provides a way to combine the
  worlds of HTML and Java servlet programming.
• JSP specs are built on the Java Servlet API.
• JSP supports two different styles for adding
  dynamic content to web pages
• JSP pages can embed actual programming code
  (typically Java)
• JSP supports a set of HTML-like tags that
  interact with Java objects on the server (without
  the need for raw Java code to appear in the
  page).

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JSP Example Hello World

• 1.
• 2.

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SimpleJSP.jsp
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SimpleJSP.jsp - the Bean edition

• JSP includes tags for interacting with JavaBeans.
• JavaBean is a simply Java class that follow
  JavaBeans specs rules for defining a Beans ctor
  methods for accessing and setting their
  properties.

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SimpleJSP.jsp - the Bean edition
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JSP Example Hello World

• In both cases the http request is
• http//localhost8080/SimpleJSP.jsp?nameNaomi
  
• The response from JSP container would be

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How it is work?

• Client request for a page ending with ".jsp.
• Web Server fires up the JSP engine.
• The JSP engine checks to see if the JSP file is
  new or changed.
• The JSP engine takes the page and converts it
  into a Java servlet (by JSP parser)
• The JSP engine compiles the servlet (by standard
  Java compiler).
• Servlet Engine executes the new Java servlet
  using the standard API.
• Servlets output is transferred by Web Server as
  a http response.

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JSP Pages content

• standard HTML tags scripts (JavaScript/VBscript)
  
• new tags for scripting in the Java language.
• Expressions
• ltexpression gt or XML variant
• ltjsp expressiongtexpression lt/jspexpressiongt
• For Example
• lt fact(12) gt
• lt (hours lt12) ? AM PM gt
• lt Math.pow(radius, 2) gt
• Scriptlets
• lt scriptlet gt or XML variant
• ltjspscriptletgt scriptlet lt/jspscriptletgt
• Declarations
• lt! declaration (s) gt or XML variant
• ltjspdeclarationgt declaration(s) lt/jsp
  declarationgt
• For Example

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JSP Pages content cont.

• JSP directives is a set of tags for providing
  the JSP container with page specific instructions
  for how the document should be processed.
  Directives affect global properties of the JSP
  page.
• lt_at_ page attr1val1 attr2 gt
• Comments for adding documentation
• Comments that will be in the output
• lt!-- comment --gt
• JSP comments
• lt-- comment --gt
• Scripting language comments
• lt / comment / gt

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JSP Pages content cont.

• Actions and implicit objects
• JSP implicit objects
• page out
• config session
• request application
• response pageContext
• exception

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JSP Pages content cont.

• Beans tags
• allows JSP pages to call reusable components
  called JavaBeans components.
• The tag ltjspuseBeangt syntax is
• ltjspuseBean id"Bean_name"
  scope"scope_value" class"class_name"
  beanName"ser_filename" type"class_or_interface_n
  ame" gt properties tags lt/jspuseBeangt
• ltjspsetPropertygt tag syntax is
• ltjspsetProperty name"property_name"
  property"property_value" /gt

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JSP benefits

• Java-based technology
• Vendor-neutral
• Full access to underlying Java platform
• Performance
• Reusable components (JavaBeans)
• Separating presentation and implementation

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Resources

• Sun JSP 1.1 Specs and description
• Server Side Java Resource Site
• IBM education courses
• JSP resource index
• JSP insider

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The end
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Scriptlet Example