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					 Introduction to
  Java Server
      Pages
   technology
            by Naomi Chen




28/1/2001                   Seminar in Databases in the Internet
                                       Environment
              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.

28/1/2001        Seminar in Databases in the Internet
                            Environment
            JSP Flow




28/1/2001   Seminar in Databases in the Internet
                       Environment
            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 user’s 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.


28/1/2001                 Seminar in Databases in the Internet
                                     Environment
             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.



                      JSP                                        ASP
Platforms             All major web platforms                    Microsoft only

Base Language         Java                                       Jscript or VBScript

Components            JSP Tags, JavaBeans, or                    COM/DCOM
                      Enterprise JavaBeans
Code Interpretation   Once                                       Each Instance



 28/1/2001                Seminar in Databases in the Internet
                                     Environment
     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
28/1/2001                Seminar in Databases in the Internet
                                    Environment
       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 API’s.,
  etc.
• Problems:
      – All document contents, both static and dynamic, reside in program
28/1/2001 source code.    Seminar in Databases in the Internet
                                 Environment
                 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).




28/1/2001               Seminar in Databases in the Internet
                                   Environment
      JSP Example: Hello World
• 1.




• 2.




28/1/2001    Seminar in Databases in the Internet
                        Environment
            SimpleJSP.jsp




28/1/2001     Seminar in Databases in the Internet
                         Environment
            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 Bean’s ctor & methods for accessing and
  setting their properties.




28/1/2001             Seminar in Databases in the Internet
                                 Environment
            SimpleJSP.jsp - the Bean
                    edition




28/1/2001          Seminar in Databases in the Internet
                              Environment
      JSP Example: Hello World
• In both cases the http request is:
    http://localhost:8080/SimpleJSP.jsp?name=Naomi
• The response from JSP container would be:




28/1/2001          Seminar in Databases in the Internet
                              Environment
                  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.
• Servlet’s output is transferred by
  Web Server as a http response.


 28/1/2001               Seminar in Databases in the Internet
                                    Environment
                     JSP Pages content
• standard HTML tags & scripts
  (JavaScript/VBscript)
• new tags for scripting in the Java language.
     – Expressions:
             <%=expression %> or XML variant:
             <jsp: expression>expression
               </jsp:expression>
            For Example:
             <%= fact(12) %>
             <%= (hours <12) ? “AM” : “PM” %>
             <%= Math.pow(radius, 2) %>
     – Scriptlets:
             <% scriptlet %> or XML variant:
             <jsp:scriptlet> scriptlet </jsp:scriptlet>
     – Declarations:
             <%! declaration (s) %> or XML variant:
             <jsp:declaration> declaration(s) </jsp:
               declaration>
28/1/2001                          Seminar in Databases in the Internet
            For Example                       Environment
            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.
     <%@ page attr1=“val1” attr2=… %>
• Comments –for adding documentation
     – Comments that will be in the output:
       <!-- comment -->
     – JSP comments
       <%-- comment --%>
     – Scripting language comments:
       <% /* comment */ %>



28/1/2001                 Seminar in Databases in the Internet
                                     Environment
            JSP Pages content – cont.
• Actions and implicit objects
     JSP implicit objects:
     page                 out
     config              session
     request              application
     response             pageContext
     exception




28/1/2001                Seminar in Databases in the Internet
                                    Environment
             JSP Pages content – cont.
• Bean’s tags
     allows JSP pages to call reusable
     components called JavaBeans components.
• The tag <jsp:useBean> syntax is:
  <jsp:useBean id="Bean_name"
  scope="scope_value" class="class_name"
  beanName="ser_filename"
  type="class_or_interface_name" > properties
  tags </jsp:useBean>
• <jsp:setProperty> tag syntax is:
  <jsp:setProperty name="property_name"
  property="property_value" />



 28/1/2001            Seminar in Databases in the Internet
                                 Environment
               JSP benefits
•   Java-based technology
•   Vendor-neutral
•   Full access to underlying Java platform
•   Performance
•   Reusable components (JavaBeans)
•   Separating presentation and implementation




28/1/2001         Seminar in Databases in the Internet
                             Environment
                 Resources
•   Sun JSP 1.1 Specs and description
•   Server Side Java Resource Site
•   IBM education courses
•   JSP resource index
•   JSP insider




28/1/2001        Seminar in Databases in the Internet
                            Environment
              The end




28/1/2001   Seminar in Databases in the Internet
                       Environment
            Scriptlet Example




28/1/2001       Seminar in Databases in the Internet
                           Environment

				
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