Java Server Pages

1
Java Server Pages

• JSP

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Topics

• JSP Overview
• JSP and Java Beans
• Servlet Integration
• JSP Scripting
• Custom Tags
• JSP and WARs/EARs

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JSP Overview

• Document-centric specification
• similar to HTML
• markup code embedded in the document
• directives
• actions
• scripts
• Java is the currently supported scripting
  language
• Complementary to servlets

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JSP Example

• ltHTMLgt
• ltHEADgtltTITLEgtJSP Examplelt/TITLEgt
• lt_at_ page import"java.util.Date" gt
• lt/HEADgt
• lt-- Embed Date in generated output --gt
• ltBODYgt
• The Date is
• lt new Date() gt
• lt/BODYgt
• lt/HTMLgt

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JSP Components

• JSP Tags
• Comments
• Scripting elements
• Actions
• Directives

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JSP Comments

• JSP comments are stripped out and do not appear
  in the generated HTML page
• lt-- This is a JSP comment --gt
• HTML comments are supported and do appear in the
  generated HTML page
• lt!-- This is an HTML comment --gt

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JSP Directives

• Instructions for JSP Container
• Processed when JSP page is converted to a servlet
• Directives do not cause information to be written
  to JSPs output
• Shorthand Form
• lt_at_ page importjavax.naming. gt
• XML Form
• ltjspdirective.page importjavax.naming. /gt

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JSP Page Directives

• Page directive attributes
• info - defines string returned from
  Servlet.getServletInfo()
• language - only required language is java
• contentType - defaults to text/htmlcharsetISO-8
  859-1
• ltjspdirective.page contentTypetext/xml/gt
• extends - specifies the base class of the
  generated servlet
• generally not a good idea, limits the container
  implementation options
• import - specifies classes to import for
  scriptlets/beans
• ltjspdirective.page importpackage.Class/gt

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JSP Page Directives (cont.)

• Page directive attributes (Cont)
• session - defines implicit HttpSession session
  variable
• ltjspdirective.page sessiontrue/gt
• buffer - specifies size of output buffer
• autoFlush - flushes (true) buffer when
  fullthrows (false) exception
• isThreadSafe - dispatches requests in single
  thread (false) or multiple threads (true).
  Default is true.
• isErrorPage - defines implicit java.lang.Throwable
  exception variable
• ltjspdirective.page errorPagetrue/gt
• errorPage - specifies JSP to invoke on uncaught
  exceptions
• ltjspdirective.page errorPage/ErrorPage.jsp/gt

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JSP Include Directives

• Static includes done at deployment
• lt_at_ include filefileRelativeURL gt
• ltjspdirective.include filefileRelativeURL /gt
• Same as include is C/C
• Imagine a page
• ltjspdirective.include fileHeader.jsp /gt
• lt jspdirective.include fileBody.jsp /gt
• lt jspdirective.include fileFooter.jsp /gt
• Another form may be done at runtimeltjspinclude
  pagepageRelativeURL/gt

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JSP Declarations

• Create variables (or methods) for later use in
  expressions or scriptlets
• lt! String choice gt
• ltjspdeclarationgt String choice
  lt/jspdeclaraiongt
• Code is inserted in generated servlet outside of
  service() method.
• Object-level scope
• Example
• ltjspdeclarationgt
• int i0
• void print() System.out.println(i)
• ltjspdeclarationgt
• ltjspscriptletgtprint()ltjspscriptletgt

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Scriptlets

• Code to be inserted directly in the generated
  servlet and executed when page is requested
• i.e. inserted in service method
• lt choice request.getParameter(Product) gt
• ltjspscriptletgt
• choicerequest.getParameter(Product)
• lt/jspscriptletgt
• Default scripting language is Java so all
  conditional statements, method invocations, etc.
  are supported

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Expressions

• Insert results from code execution directly onto
  the JSP Page
• ltPgt
• The Date is lt new Date() gt
• lt/Pgt
• ltPgt
• The Date is ltjspexpressiongtnew
  Date()lt/jspexpressiongt
• lt/Pgt
• Automatically converts toString() and writes
  result

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Implicit Objects

• page
• Pages servlet instance
• config
• ServletConfig (configuration data)
• request
• HttpServletRequest
• response
• HttpServletResponse

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Implicit Objects (Cont)

• out
• Output Stream for content (JspWriter)
• session
• HttpSession
• application
• ServletContext
• pageContext
• Context Data for page execution (PageContext)
• exception
• Available on error pages (java.lang.Throwable)

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Implicit Object Example

• ltHTMLgt
• ltBODYgt
• lt String visitorrequest.getParameter(name)
• if( visitornull) visitorUnknown gt
• Hello, lt visitor gt
• lt/BODYgt
• lt/HTMLgt
• http//localhost7001/jsp/implicit.jsp?nameDan
• Remember Keep URLs shorter than 255 characters

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JSP-Specific Tags

• jspforward
• Switch to another URL
• jspinclude
• Embed the contents of another URL in this page
• jspuseBean, jspsetProperty, jspgetProperty
• Embed and use JavaBeans in a JSP Page
• jspplugin
• downloads Java plugin to client

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Risks

• Embedding code in the HTML page is convenient,
  but .
• We are mixing business logic with presentation
• Use JSP for simple coding e.g. Date
• Defer business logic to Beans and or Servlets

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JSP and Java Beans
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What is a Bean?

• Java class that follows a set of implementation
  and naming guidelines
• Typically named xxxBean
• Public no argument constructor
• Setters/Getters for attributes
• Indexed properties
• BeanInfo interface
• Should implement java.io.Serializable
• Event model, bound and constrained properties

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HelloBean
packages corej2ee.examples.web.usebean public
class HelloBean implements java.io.Serializable
String name public HelloBean()
nameAnonymous public String getName()
return name public void setName(String
argName) nameargName
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usebean.html
lthtmlgt ltheadgtlttitlegtTest of jsp use
beangtlt/titlegtlt/headgt ltbodygt lth1gtEnter
Namelt/h1gt ltform action"usebean.jsp"
method"POST"gt lttable border"0"
width"30" cellspacing"3" cellpadding"2"gt
lttrgtlttdgtltbgtUser Namelt/bgtlt/tdgt
lttdgtltinput type"text" size"20"
name"name"gtlt/tdgtlt/trgt
lttrgtlttdgtltpgtltinput type"submit"
value"Login"gtlt/tdgtlt/trgt lt/tablegt
lt/formgt lt/bodygt lt/htmlgt
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Using Java Beans in JSP

• ltjspuseBean id"hellobean" class"corej2ee.exampl
  es.web.usebean.HelloBean"/gt
• ltjspsetProperty namehellobean property"name"
  param"name"/gt
• ltHTMLgt
• Hello, ltjspgetProperty name"hellobean"
  property"name"/gt
• ltBODYgt
• lt/BODYgt
• lt/HTMLgt

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Setting Bean Attributes

• jspsetProperty tag
• Can initialize bean properties from HttpRequest
• ltjspsetProperty namehello propertyname
  paramname/gt
• Param attribute (from form) is the equivalent of
• request.getParameter(name)
• Property attribute (from JavaBean) is equivalent
  of
• hello.setName()
• Shortcut to set all parameters in bean that match
  request parameter names
• ltjspsetProperty namehello property/gt
• Use value attribute to set the property to a
  specific value
• propertyname valuehard-coded-value

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Bean Scope

• Bean lifetime defaults to the execution of the
  page that contains the useBean tag
• scope
• page - defined in jsp.PageContext
• request - defined in Servlet.service()s
  request object
• (jspforward, jspinclude)
• session - defined in users session object
• application - defined in Servlets Context
• Interesting servlet/jsp communication mechanism

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Benefits and Limitations

• Benefits
• Separates business logic from HTML content
• Easier maintenance
• Component Re-usability
• Can be configured with commercial tools
• Limitations
• Java Bean event model not supported

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JSP Summary

• Allows HTML authors to be HTML authors and not
  Java programmers
• While Java code can be embedded in the .jsp page
  this should be kept to a minimum
• Use JavaBeans for model data and tags as the
  interface between the html page and the model
• Avoid HTML output from Beans
• Custom Tags are useful for generating HTML

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JSP Custom Tags
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JSP Tags Overview

• Capability to define your own jsp tags in a
  portable manner
• Required components
• Tag Handler class
• Implements tag behavior
• Tag Library Descriptor File
• Define class to server and associate it with an
  XML tag name
• XML document

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Tag Handler

• Must implement the javax.servlet.jsp.tagext.Tag
  interface
• doStartTag() and doEndTag() are key methods
• Frequently extend TagSupport

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Handler Example (DebugTag.java)

• package corej2ee.examples.web.tag
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import javax.servlet.
• / A tag that includes the body content only if
• the "debug" request parameter is set.
• ltPgt
• Taken from Core Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.coreservlets.com/.
• copy 2000 Marty Hall may be freely used or
  adapted.
• /

• public class DebugTag extends TagSupport
• public int doStartTag()
• ServletRequest request pageContext.getReques
  t()
• String debugFlag request.getParameter("debug
  ")
• if ((debugFlag ! null)
• (!debugFlag.equalsIgnoreCase("false")))
• return(EVAL_BODY_INCLUDE)
• else
• return(SKIP_BODY)

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TagLib Descriptor FileWEB-INF/csajsp-taglib.tld
lt?xml version"1.0" encoding"ISO-8859-1"
?gt lt!DOCTYPE taglib PUBLIC "-//Sun Microsystems,
Inc.//DTD JSP Tag Library 1.1//EN"
"http//java.sun.com/j2ee/dtds/web-jsptaglibrary_1
_1.dtd"gt lttaglibgt lttlibversiongt1.0lt/tlibversion
gt ltjspversiongt1.1lt/jspversiongt
ltshortnamegtcsajsplt/shortnamegt lturigtlt/urigt
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WEB-INF/csajsp-taglib.tld (Cont)

• ltinfogt
• A tag library from Core Servlets and
  JavaServer Pages,
• http//www.coreservlets.com/.
• lt/infogt
• lttaggt
• ltnamegtdebuglt/namegt
• lttagclassgtcorej2ee.examples.web.tag.DebugTaglt/
  tagclassgt
• ltbodycontentgtJSPlt/bodycontentgt
• ltinfogtIncludes body only if debug param is
  set.lt/infogt
• lt/taggt
• lt/taglibgt

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web.xml entry
lt?xml version"1.0" ?gt lt!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application
2.3//EN " "http//java.sun.com/j2ee/dtds/web-app_2
_2.dtd"gt ltweb-appgt lttaglibgt
lttaglib-urigtcsajsp-taglib.tldlt/taglib-urigt
lttaglib-locationgtWEB-INF/csajsp-taglib.tldlt/taglib
-locationgt lt/taglibgt lt/web-appgt
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DebugExample.jsp

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of SimplePrimeTag tag.
• Taken from Core Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.coreservlets.com/.
• copy 2000 Marty Hall may be freely used or
  adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtUsing the Debug Taglt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• ltBODYgt

• ltH1gtUsing the Debug Taglt/H1gt
• lt_at_ taglib uri"csajsp-taglib.tld"
  prefix"csajsp" gt
• Top of regular page. Blah, blah, blah. Yadda,
  yadda, yadda.
• ltPgt
• ltcsajspdebuggt
• ltBgtDebuglt/Bgt
• ltULgt
• ltLIgtCurrent time lt new java.util.Date() gt
• ltLIgtRequesting hostname lt request.getRemoteHo
  st() gt
• ltLIgtSession ID lt session.getId() gt
• lt/ULgt
• lt/csajspdebuggt
• ltPgt
• Bottom of regular page. Blah, blah, blah. Yadda,
  yadda, yadda.
• lt/BODYgtlt/HTMLgt

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Invoking debug.jsp
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Invoking debug.jsp with Debug
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Tag Complexity

• Tags can become very complicated
• Can parse body themselves
• Can become nested in other tags
• Ex. IF/THEN/ELSE
• Looping constructs
• While beans are generally used for model data and
  shared information, tags are typically confined
  to a single page

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Tag Summary

• Tags are a portable extension mechanism for jsp
• Can build a library of components
• Ex. XSLT renderer of XML data
• Bridge to JavaBean model data
• Ex. Setting indexed properties
• Further eliminates the need for HTML authors to
  learn Java

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JSTL and Expression Language

• Optional Topic

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JSP Standard Tag Library

• Encapsulates core functionality for many web
  applications in custom tags
• http//java.sun.com/products/jsp/jstl
• Requires JSP 1.2
• Custom tags
• Iteration, Control, Internationalization,
  Database Access
• Expression language to simplify page development

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JSTL Libraries

• Core
• XML Processing
• I18N
• Database Access

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Expression Language

• Simpler syntax for accessing Java Bean properties
• Similar to JavaScript
• customerBean.name
• customerBeanname
• customerBean is in one of the JSPs scopes
• page, request, session, or application
• Implicit variables also available
• param collection of all request parameters
• cookie collection of all cookies
• header collection of all request headers

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Basic Example (e1.jsp)

• lt_at_ taglib uri"myTLD" prefix"c" gt
• lthtmlgt
• ltheadgt
• lttitlegtJSTL Basic EL Supportlt/titlegt
• lt/headgt
• ltbody bgcolor"FFFFFF"gt

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lth1gtBasic EL exampleslt/h1gt cookie.JSESSIONID.val
ue ltcout value"cookie.JSESSIONID.value"
/gt ltBRgt param'name' ltcout
value"param'name'" /gt ltBRgt header'User-Ag
ent' ltcout value"header'User-Agent'"
/gt ltBRgt lt/bodygt lt/htmlgt
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Iteration Example (IterateSetup.jsp)
lt_at_ page import"corej2ee.examples.web.jspstl.,
java.util.List,
java.util.ArrayList" gt lt STLPerson
personnew STLPerson() person.setName("Dan")
person.setStreet("Poplar Ridge")
person.setZip("21122")
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STLPerson person2new STLPerson()
person2.setName("Jim") person2.setStreet("Seve
rna Park") person2.setZip("21046") List
peopleListnew ArrayList() peopleList.add(pers
on) peopleList.add(person2)
request.setAttribute("people", peopleList) gt ltjs
pinclude page"Iterate.jsp" /gt
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Iterate.jsp
lt_at_ taglib uri"myTLD" prefix"c"
gt lthtmlgt ltheadgt lttitlegtJSTL Iteration
Examplelt/titlegt lt/headgt ltbody bgcolor"FFFFFF"gt lt
h3gtSimple Iterationlt/h3gt lth4gtPeople listlt/h4gt
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ltTABLE BORDER"1"gt ltTRgtltTDgtNamelt/TDgtltTDgtStreetlt/
TDgtltTDgtZiplt/TDgtlt/TRgt ltcforEach var"person"
items"people" gt ltTRgt ltTDgtltcout
value"person.name" /gtlt/TDgt ltTDgtltcout
value"person.street" /gtlt/TDgt ltTDgtltcout
value"person.zip" /gtlt/TDgt
lt/TRgt lt/cforEachgt lt/TABLEgt lt/bodygt lt/htmlgt
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JSP and J2EE
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JSP and WARs

• JSPs can be treated like a static resource and
  grouped with html and image files in the WAR
• JSPs can also be configured like servlets in the
  WAR file to
• Map to a URL
• Receive initialization parameters, etc.
• ltservletgt     ltservlet-namegtmyFoolt/servlet-na
  megt     ltjsp-filegtmyJSPfile.jsplt/jsp-filegtlt/serv
  letgt
• ltservlet-mappinggt     ltservlet-namegtmyFoolt/
  servlet-namegt     lturl-patterngt/mainlt/url-pattern
  gtlt/servlet-mappinggt

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Web Architectures
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Session EJB
Action/ Worker Servlet
Java Bean
Controller Servlet
HTTP
Entity Beans
DAO
View JSP
Custom Tags
Database
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JSP Summary

• Page-centric technology for dynamic web pages
• Avoid Java code in JSP pages
• Use Java Beans
• Custom Tags
• STL
• For mid-large sites use MVC architecture
• Servlets for getting work done
• JSP for page templates