Struts Basics

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Struts Basics

• COSC 617
• Created by Marc Zhang
• Lianjiang Zong
• Yedong Tang

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Struts Basics

• What is and Why Struts?
• Struts architecture
• Controller
• View
• Model
• Struts application
• Example

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Overview of Struts

• open source
• A framework
• For building web application
• Advantage

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What is Struts?

• Struts Frame work is the implementation of
  Model-View-Controller (MVC) design pattern for
  the JSP.
• Struts is maintained as a part of Apache Jakarta
  project and is open source.
• Struts Framework is suited for the application of
  any size.

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Why Struts?

• Takes much of the complexity out of building
  your own MVC framework
• Encourages good design practice and modeling
• Easy to learn and use
• Feature-rich
• Many supported 3rd-party tools

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Why Struts? Cont.

• Flexible and extensible
• Large user community
• Stable and mature
• Open source
• Integrates well with J2EE
• Good taglib support

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Why Struts? Cont.

• Works with existing web apps
• Easy to retain form state
• Unified error handling programmatically and
  declaratively
• Integration with Tiles framework
• Clear delineation of responsibility makes long
  term maintenance easier (more modular)

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Struts architecture

controller
model
view
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Struts architecture

• Base on MVC design pattern
• 3 Major Components in Struts
• Servlet controller (Controller)
• Java Server Pages or any other presentation
  technology (View)
• Application Business Logic in the form of
  whatever suits the application (Model)

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Advantages of Struts architecture

• dividing application components into three
  different categories Model
• component is independent of the other component
• Changes in one component will have no or less
  impact on other component

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• Components of Controller, Model and view

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Responsibilities and components of Model

• Model
• providing the data from the database
• saving the data into the data store
• content
• Data access
• Data validation
• data saving logic

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Responsibilities and components of View

• content
• HTML
• JSPs
• Custom Tag Libraries
• Resources files

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Responsibilities and components of View cont.

• View
• represents view of users application
• taking the input from the user
• dispatching the request to the controller
• receiving response from the controller
• displaying the result to the user

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Responsibilities and content of Controller.

• Content
• ActionServlet(Provided by Struts)
• Action(Provided by developer)
• RequestProcessor(Provided by Struts)
• Action Mapping(Specified by developer)

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Responsibilities and components of Controller

• Controller
• receiving the request from client
• executing the appropriate business logic from
  the Model
• producing the output to the user using the View
  component

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ActionServlet

• Performs the role of Controller
• Delegates most of this grunt work to Action
  classes
• Is responsible for initialization and clean-up
  of resources

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RequestProcessor

• processPath
• processLocale
• processContent
• processNoCache
• processPreprocess
• processMapping
• processRoles

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RequestProcessor cont.

• processActionForm
• processPopulate
• processValidate
• processForward
• processInclude
• processActionCreate
• processActionPerform
• processForwardConfig

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Action Mapping

• three important elements of struts-config.xml
  used to describe actions
• ltform-beansgt
• ltaction-mappinggt
• ltglobal-forwardsgt

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ActionForm Bean

• Define an ActionForm bean for the input form in
  struts-config.xml file
• Contains only property getter and property
  setter methods for each field-no business logic
• Provides validation mechanism

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Action

• a Java class that does the work of your
  application
• Handle request
• Perform business logic
• Simple action class
• Sophisticated action class

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execute() method of Action class

• Perform the processing required to deal with the
  request
• Update the server-side objects (Scope variables)
  that will be used to create the next page of the
  user interface
• Return an appropriate ActionForward object

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Model Components

• Model divided into concepts
• Internal state of the system
• Business logic that can change that state
• Internal state of system represented by
• JavaBeans
• Enterprise JavaBeans
• POJO's
• JDO
• JDBC
• Whatever

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Model Components (cont.)

• JavaBeans,Enterprise JavaBeans

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Model Components (cont.)

• JavaBeans and Scope
• Page visible within a single JSP page, for the
  lifetime of the current request
• Request visible within a single JSP page, as
  well as to any page or servlet that is included
  in this page, or forwarded to by this page
• Session visible to all JSP pages and servlets
  that participate in a particular user session,
  across one or more requests
• Application - visible to all JSP pages and
  servlets that are part of a web application

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Model Components (cont.)

• JSP pages and servlets in the same web
  application share the same sets of bean
  collections
• Example
• Servlet code
• MyCart mycart new MyCart(...)
• request.setAttribute("cart", mycart)
• JSP page
• ltjspuseBean id"cart" scope"request"
• class"com.mycompany.MyApp.MyCart"/gt

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Model Components in StrutsFramework

• SystemState Bean
• This is a conceptual term Struts does not
  provide any programming API.
• Struts does not define formal class of this
• Defines the current state
• Could be represented as a set of one or
  more
• JavaBeans classes, whose properties define
  the
• current state

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Model Components in StrutsFramework(cont.)

• Example a shopping cart system
• Contains a bean that represents the cart being
  maintained for each individual shopper
• Includes the set of items that the shopper has
  currently selected for purchase
• BusinessLogic Bean
• This is a conceptual term Struts does not
  provide any programming API

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Model Components in StrutsFramework(cont.)

• Struts does not define formal class of this
• Can be an ordinary JavaBean
• Can be stateful or stateless EJB
• Encapsulates functional logic of an application
  using method calls
• Action object should translate the HTTP request
  then call BusinessLogic bean
• Ideally should be designed so that they do not
  know they are being executed in a web application
  environment
• should not refer any Web application objects
• enhanced reusability

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View Components
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View Components cont.

• JSP files which you write for your specific
  application
• Set of JSP custom tag libraries
• Resource files for internationalization
• Allows for fast creation of forms for an
  application
• Works in concert with the controller Servlet

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View Components cont.

• ActionForward object tells Servlet controller
  which JSP page is to be dispatched to
• JSP pages use ActionForm beans to get output
  Model data to display
• Struts contains a series of tag libraries
• Facilitates communication between HTML
  designers and developers
• Facilitates dynamic Web content

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Forms and FormBean Interactions

• How do you reflect the previous value a user has
  entered in a subsequent page?
• If a user makes an error in only one field
  in page among the multiple fields, the
  application should allow him to fix just that
  field
• With just JSP, you have to do
• ltinput type"text" name"username"
• value"lt loginBean.getUsername() gt"/gt
• With Struts, you can do
• lthtmltext property"username"/gt

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Example submit.jsp

• 1 lt_at_ page language"java" gt
• 2 lt_at_ taglib uri"/WEB-INF/struts-bean.tld"
  prefix"bean" gt
• 3 lt_at_ taglib uri"/WEB-INF/struts-html.tld"
  prefix"html" gt
• 4 lt_at_ taglib uri"/WEB-INF/struts-logic.tld"
  prefix"logic" gt
• 5
• 6 lthtmlgt
• 7 ltheadgtlttitlegtSubmit examplelt/titlegtlt/headgt
• 8 ltbodygt
• 9
• 10 lth3gtExample Submit Pagelt/h3gt
• 11
• 12 lthtmlerrors/gt
• 13
• 14 lthtmlform action"submit.do"gt
• 15 Last Name lthtmltext property"lastName"/gtltbrgt
  
• 16 Address lthtmltextarea property"address"/gtltbr
  gt
• 17 Sex lthtmlradio property"sex"
  value"M"/gtMale
• 18 lthtmlradio property"sex" value"F"/gtFemaleltbr
  gt
• 19 Married lthtmlcheckbox property"married"/gtltbr
  gt

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Struts Tags

• Tag Libraries Overview
• Number of taglibs included as part of Struts
  Usage is not required, but helpful
• Bean tags Tags for accessing Beans and their
  properties
• Html tags Form bridge between JSP view and
  other components
• Logic tags Provides presentation logic tags
  that eliminate need for scriptlets
• Template tags Tags to form JSP templates that
  include parameterized content
• Nested Tags Allows for object hierarchy and
  helpful for rendering lists of lists

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When to JSTL in your Strutsapplication?

• Developers should evaluate when to use the JSTL
  (JavaServer Pages Standard Tag Library )
• Many of the Struts taglib features are now
  available in the JSTL
• Its simple If the tag exists in the JSTL use
  it
• Continue using the Struts tags where appropriate,
  they will continue to be supported

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Interaction with JSTL

• Struts-el taglibs allow for using expression
  values instead of just rtexprvalue
• Runtime ltbeanmessage key'lt stringvar
  gt'/gt
• Expression ltbean-elmessage
  key"stringvar"/gt
• Set of optional taglibs that can be used with
  the JSTL expression language (EL)
• Implements many (but not all) of the Struts tags.
• Located in the contrib folder of the Struts
  release
• Container with servlet 2.3 support required

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Access to Tag Libraries

• All tag libraries are defined in web.xml using
• lttaglibgt element
• lt!-- Struts Tag Library Descriptors --gt
• lttaglibgt
• lttaglib-urigt/WEB-INF/struts-bean.tldlt/taglib-uri
  gt
• lttaglib-locationgt/WEB-INF/struts-bean.tldlt/tagli
  b-locationgt
• lt/taglibgt
• lttaglibgt
• lttaglib-urigt/WEB-INF/struts-html.tldlt/taglib-uri
  gt
• lttaglib-locationgt/WEB-INF/struts-html.tldlt/tagli
  b-locationgt
• lt/taglibgt

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Bean Tags

• Tags for accessing beans and their properties
• Enhancements to ltjspuseBeangt
• Convenient mechanisms to create new beans based
  on the value of
• Cookies
• Request Headers
• Parameters

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HTML Tags

• Form bridge between JSP view and other components
• Input forms are important for gathering
  userentered data
• Most of the actions of the HTML taglib involve
  HTML forms
• Error messages, hyperlinking, internationalization
  
• HTML tags must be nested within a form tag
• inform tag handler which bean to use for
  initializing displayed values

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Logic Tags

• Provides presentation logic tags that eliminate
  need for scriptlets
• Value comparisons Include ! lt gt lt gt
• Substring matching match, not match
• Presentation logic forward, redirect
• Collections iterate

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Template Tags

• Templates are JSP pages that include
  parameterized content
• Useful for creating dynamic JSP templates for
  pages that share a common format
• Functionality provided is similar to what can be
  achieved using the standard JSP include
  directive, but these tags allow for dynamic
  rather than static content

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Template Tags cont.

• Three template tags work in an interrelated
  function
• Get - Gets the content from request scope
  that was put there by a put tag.
• Insert - Includes a template
• Put - Puts content into request scope

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DynaActionForm

• Issues with using ActionForm
• ActionForm class has to be created in Java
  programming language
• For each HTML form page, a new ActionForm
  class has to be created
• Every time HTML form page is modified (a
  property is added or removed), ActionForm class
  has to be modified and recompiled
• DynaActionForm support is added to Struts 1.1 to
  address these issues

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What is DynaActionForm?

• org.apache.struts.action.DynaActionForm
• extends ActionForm class
• In DynaActionForm scheme,
• Properties are configured in configuration
  file rather than coding
• reset() method resets all the properties
  back to their initial values
• You can still subclass DynaActionForm to
  override reset() and/or validate() methods
• Version exists that works with Validator
  framework to provide automatic validation

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Types Supported byDynaActionForm

• java.lang.BigDecimal, java.lang.BigInteger
• boolean and java.lang.Boolean
• byte and java.lang.Byte
• char and java.lang.Character
• java.lang.Class, double and java.lang.Double
• float and java.lang.Float
• int and java.lang.Integer
• long and java.lang.Long
• short and java.lang.Short
• java.lang.String
• java.sql.Date, java.sql.Time, java.sql.Timestamp

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Struts Validator

• The Struts Validator, in some form, has been
  available since the days of Struts 0.5. It was
  originally packaged as a developer contribution.
  Later, the core code was moved to the Jakarta
  Commons and a Struts specific extension became
  part of Struts since 1.1.

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How to perform Validation withDynaActionForm?

• DynaActionForm does not provide default behavior
  for validate() method
• You can subclass and override validate()
  method but it is not recommended
• Use Validator Framework
• Use DynaValidatorForm class (instead of
  DynaActionForm class)
• DynaValidatorForm class extends
  DynaActionForm and provides basic field
  validation based on an XML file