CISH6960: Developing Enterprise Applications

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CISH-6960 Developing Enterprise Applications

• Lecture 4
• June 5, 2004

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JSTL

• The JSP Standard Tag Library

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Introduction

• Minimize application logic in JSP Pages
• Standard action sequence unwieldy
• JSP 2.0 Expression Language (EL)
• Minimal syntax for reading information
• JSP Standard Tag Library (JSTL) provides custom
  actions
• Can now replace most scriptlets

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JSP Expressions

• General form, embedded in JSP
• expression
• ltpgtThe value of myBeans name property is
  myBean.name.lt/pgt
• Can be passed in an attribute value
• ltfmtformatDate valuejob.completion /gt
• EL syntax is mostly intuitive
• Borrows from ECMAScript and XPath

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Indexing

• To read a property, use the dot operator
• a.b
• ltjspgetProperty namea propertyb /gt
• To read an indexed property, use
• myCollection5
• myBean.myIndexedProperty3
• Dot and bracket equivalent
• a.b
• ab
• Bracket useful where dot doesnt work

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Operators

• EL supports arithmetic and logical operators
• Arithmetic
• , -, , /, div, , mod
• Logical
• , , !, and, or, not
• Use parentheses where precedence not obvious
• x (y z)
• Empty operator
• empty A is true if A is null or a collection
  with no elements

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Implicit Objects

• Set of objects provided by the container
• All available as simple maps
• Can use either dot or bracket notation
• cookiecustomerName
• Some common objects
• pageContext
• requestScope
• sessionScope
• applicationScope
• param
• initParam

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Hello, EL
lthtmlgt ltheadgtlttitlegtHello, EL!lt/titlegtlt/headgt ltb
odygt lth1gtHello, param"name"!lt/h1gt lt/bodygt
lt/htmlgt
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Some EL Examples

• a.b
• myCollection5
• myBean.myIndexProperty3
• yourBean.location.path
• thisthat.member.collection4
• parampreferences.keyParameter
• requestScope.forwardedValue
• sessionScope.mySessionAttribute
• x ( y z )
• empty myCollection

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JSTL

• Custom tag libraries came from many sources
• Sun decided to adopt a standard set
• JSP 2.0 containers provide native support for
  them
• Earlier containers use tag library jar and tld
  files, like any other tag library
• Standard version from Apache

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JSTL Namespaces

• Four distinct libraries, each with its own
  namespace and suggested prefix
• Namespace prescribed in JSTL spec
• Prefix arbitrary, but very common
• Each imported into a JSP page with the normal lt_at_
  taglib gt directive

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JSTL Namespaces
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Using JSTL

• Taglib directive to import library
• Required attribute prefix
• Then use either uri as above, or
• Attribute tagdir points to subdirectory with
  tld (tag library descriptor) files
• lt_at_ taglib prefixc urihttp//java.sun.com/jst
  l/core gt

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Core Library

• Actions
• ltcset target property scope
  value /gt
• Much like ltjspsetPropertygt
• Can also declare a new variable
• Cannot instantiate an object, so not like
  ltjspuseBeangt
• ltcif testgtlt/cifgt
• Also available are ltcchoosegt, ltcwhengt, and
  ltcotherwisegt
• ltcforEach varitem itemssessionScope.cart.i
  temsgt lttrgtlttdgtitem.quantitylt/tdgtlt/trgtlt/cfo
  rEachgt

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Using JavaBeans with JSTL

• Heres the cool part
• Using EL with beans will find a bean in any scope
• Can use the ltjspuseBeangt tag to instantiate a
  bean
• Then myBean.property finds the bean regardless
  of scope

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Formatting Library

• Used for
• Formatting output
• Localization
• Internationalization
• ltfmtsetLocalegt sets default locale
• ltfmtsetTimeZonegt
• ltfmtformatDate valuenow /gt
• Assumes we already did ltjspuseBean idnow
  classjava.util.Date /gt

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XML Library

• Can parse and transform XML
• Use with ltcimportgt can be very powerful
• ltcimport url/books.xml varxml /gtltxparse
  docxml varbooklist scopeapplication /gt

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XML Library

• XML library understands XPath expressions
• Major improvement over JSP, and even the standard
  XML parsers in general

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XML Parsing
lt_at_ taglib prefix"c" uri"http//java.sun.com/jst
l/core_rt" gt lt_at_ taglib prefix"x"
uri"http//java.sun.com/jstl/xml_rt" gt lttable
bgcolor"FFFFFF" cellpadding"4"
border"1"gt ltcimport var"source"
url"Listings.xml" /gt ltxparse var"doc"
xml"source" /gt ltxforEach var"unit"
select"doc//housingUnitbedrooms
parambedrooms and rent lt paramrent"
gt lttrgt lttdgtltxout select"unit/location/streetA
ddress" /gtlt/tdgt lttdgtltxout select"unit/rent"
/gtlt/tdgt lt/trgt lt/xforEachgt lt/tablegt
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Servlet Filters

• Modifying Requests and Responses

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Filters

• Introduced in Servlet 2.3 spec
• Reusable Java classes which can transform HTTP
  requests before they reach their destinations
• Configured as a chain
• Each filter acts, then calls next in chain

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Filters
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Uses for Filters

• Authentication
• Logging and auditing
• Data compression
• Encryption / Decryption
• XML Transformation
• Localization
• Image conversion
• Caching

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Filter Interface

• Three methods
• init( FilterConfig )
• destroy()
• doFilter( ServletRequest, ServletResponse,
  FilterChain )
• Like the service method in Servlet

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Filter Lifecycle

• Declared in deployment descriptors
• Associated with a servlet or a URL pattern
• Container instantiates single instance
• Container calls init() method
• Filter serves incoming requests through
  doFilter()
• If container unloads the filter, destroy() is
  called

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Using Filters

• Do any required initialization in init()
• In doFilter(), be sure to call chain.doFilter()
  to call the next filter in the chain
• In deployment descriptor, declare ltfiltergt and
  ltfilter-mappinggt
• ltfiltergt associates name with class
• ltfilter-mappinggt associates filter name with
  ltservlet-namegt or lturl-patterngt
• Note that request, response are arguments
• Can add parameters, modify request, etc.