Basic JSP

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Basic JSP
Celsina Bignoli bignolic_at_smccd.net
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Problems with Servlets

• Servlets contain
• request processing,
• business logic
• response generation
• all lumped together!
• Problems
• good Java knowledge is needed to develop and
  maintain the application
• changing look and feel or a new client type
  require changes to the Servlet code
• cannot use web page development tools

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Advantages of JSP

• separates request processing and business logic
  from the presentation
• places all static HTML in a JSP page and adds a
  few JSP elements to generate the dynamic content
• allows the separation of tasks between Java
  programmers and WEB page authors
• makes it easier to change presentation without
  affecting business layer and viceversa

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A Simple JSP Page
JSP tag
lt_at_ page importjava.text., java.util.gt
lthtmlgt
ltheadgtlttitlegtltDate Examplelt/titlegtlt/headgt
HTML
ltbodygt
Scriptlet
Today is ltemgtlttodaygtlt/emgt lt/bodygt lt/htmlgt
Example.jsp

• Static HTML/XML elements
• Dynamic scriptlets
• Special JSP elements

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JSP Processing- Translation Phase
request
response
JSP Page (.jsp)
JSP Translator
Text Buffer
Java Compiler
Servlet Source (.java)
Servlet Class (.class)
JVM
Servlet Container
Translation Phase
Request Processing Phase
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JSP Processing- Request Processing Phase
request
response
JSP Page (.jsp)
JSP Translator
Text Buffer
Java Compiler
Servlet Source (.java)
Servlet Class (.class)
JVM
Servlet Container
Translation Phase
Request Processing Phase
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JSP Translation - Example

• package jsp
• import javax.servlet.
• import javax.servlet.http.
• import java.text.
• import java.util.
• public class example_jsp
• extends org.apache.jasper.runtime.HttpJs
  pBase

example_jsp.java
extends javax.servlet.http.HttpServlet
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service() method - Example

• public void _jspService(HttpServletRequest
  request,
• HttpServletResponse
  response)
• throws IOException,
  ServletException
• try
• out pageContext.getOut()
• out.write("lthtmlgt\r\n")
• out.write("ltheadgtlttitlegtltDate
  Examplelt/titlegtlt/headgt\r\n")
• out.write("ltbodygt\r\n")
• Date dnew Date()
• String today DateFormat.getInstance().form
  at(d)
• out.write("\r\n")
• out.write("Today is\r\n")
• out.write("ltemgt")
• out.print(today)
• out.write("lt/emgt\r\n")
• out.write("lt/bodygt\r\n")

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JSP Elements

• Directives
• Comments
• Actions
• standard actions
• custom actions and JSTL
• Expression Language (EL)
• Scripting
• JavaBean components

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JSP Directive Elements

• Specify attribute of the page itself
• type of content
• buffering requirements
• resources used
• how runtime errors should be handled
• Do not affect content of a response but how the
  container should handle it.
• Enclosed between lt_at_ and and gt
• Have a name and one or more attribute/value pairs
  
• attribute and values are case-sensitive
• values must be enclosed in single or double quotes

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Page Directive

• lt_at_page contentTypetext/html gt
• other possible values for contentType
• text/plain
• text/xml
• text/vnd.wap.wml
• other possible attributes
• errorPage
• isErrorPage
• session
• pageEncoding
• buffer
• autoFlush

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Taglib Directive

• lt_at_taglib prefixc urihttp//java.sun.com/jsp/
  jstl/core gt
• declares a JSTL custom tag library used in the
  page
• the prefix is the name used for the library in
  the JSP page
• the uri uniquely identifies the library

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JSP Comments

• lt-- comment goes here --gt
• delimited by lt-- and --gt
• ignored when the page is processed
• never sent to the browser

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JSP Actions

• represent dynamic actions to be performed at
  runtime
• ltprefix action-name attr1value1
  attr2value2gt
• action_body
• lt/brefixaction-namegt
• or
• ltprefix action-name attr1value1
  attr2value2gt
• allows dor actions in different libraries to have
  the same name
• allow contaienr to determine which library an
  action belongs

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Standard Actions

• ltispuseBeangt
• makes a java bean component available to a page
• ltjspgetPropertygt
• gets a property value from a JavaBean components
  and adds it to the response
• ltjspsetPropertygt
• Set a JavaBean property value
• ltjspincludegt
• Include the response from a servlet or JSP page
  during the request processing phase
• ltjspforwardgt
• Forwards the processing of a request to a servlet
  or JSP page

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Standard Actions (2)

• ltispparamgt
• adds a parameter to a request handed over to
  another servlet or JSP page
• ltjspplugingt
• Used to run applets on the browser
• ltjspattributegt
• Set the value of an action attribute
• ltjspbodygt
• Sets the action element body
• ltjspelementgt
• Dynamically generate an XML element
• ltjsptextgt
• to encapsulate text verbatim

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JSP Standard Tag Library (JSTL)

• group of libraries each containing related
  actions
• Core
• XML processing
• Internationalization
• Relational Database Access
• Functions

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JSP Expression Language

• based on both ECMAScript and XPath
• built-in support for JavaBean access and
  manipulation, collection of objects, automatic
  type conversion etc
• EL expressions enclosed within and
• anObject.aProperty
• ltcif testuser.salary gt 10000gt
• lt/Cifgt

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Scripting Elements

• fragments of java code embedded in a JSP page
• Declarations
• Expressions
• Scriptlets
• heavily used in early JSP pages but rarely in
  newer developments (and discouraged)

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Declarations

• used to insert methods, constants and variable
  declarations in JSP pages
• lt!
• private static String EXAMPLE/example2
• private static String SHOP_PAGE/estore.jsp
• private static String CART_PAGE/shopcart.jsp
  
• private String dispPrice(String price)
• // method body
• gt

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Expressions

• an embedded Java expression that is evaluated and
  converted to a text String
• The text string is placed in the JSP output at
  the location in which the element appears
• lttablegt
• lttrgt
• lttdgt lt curItem.getName() gt lt/tdgt
• lttdgt lt String.valueOf(dispPrice(curItem.getPrice
  ())) gt
• lt/tdgt
• lt/trgt
• lt/tablegt

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Scriptlets

• used to include complete fragments of java code
  in a JSP page
• cau use the out implicit object (of type
  javax.servlet.jsp.JspWriter) to write output
• lt
• if (state.isLocal())
• out.print(totalCost localTax)
• else
• out.print(totalCost)
• gt

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Problems with Scriptlets

• discouraged since they do not promote separation
  of presentation from data/logic
• look as a Servlet inside-out
• make JSP page as hard to write/maintain as
  corresponding Servlet

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Model-View-Controller Design

• Separation of
• data and business logic (Model)
• data presentation (View)
• data interaction (Controller)
• The user interacts with the Controller to ask for
  things to be done.
• Controller forward the request to the Model
• the result of the request is displayed by the View

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Model-View-Controller Design
Controller (Servlet)
Data
Request
Model (JavaBean)
Response
View (JSP)
Data
Data Tier
JSP/Servlet Container
Browser