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Notes from a Study of Jakarta Struts

Struts

  • Uses the Servlet MVC framework
  • Tailored for web appilcations
Top Level Struts Packages

  • action: eg: Actionform, action messages- Controller classes
  • actions: -Out of box Action classes eg: Dispatcher action
  • config-configuration file
  • taglib
  • Tiles
  • upload- uploading/downloading from a browser
  • util-General purpose utility classes
  • validator: Struts specific extension classes when deploying the validator
Controller Components
  • Receive a client request,invoke a business operation, coordinate view to return to client
  • Many struts controller components
  • example: org.apache. struts. action. ActionServlet


    ActionServlet
    • extends javax.servlet.http:HttpServlet
    • not abstract
    • Configured in deployment descriptor
    • All controller requests processed by helper classes- decendants of Action class
  • Request Processor
    • org.apache. struts. action. RequestProcessor
    • Version 1.1 onwards
    • Together with ActionServlet called Controller
  • Struts Action Classes
    • org.apache. struts. action. Action
    • Not abstract
    • Extension of Controller component
    • bridge or decoupler-client-user action, business operation
    • Allows more than One to one action between user action and business action
    • execute() menthod-
      public ActionForward execute(ActionMapping mapping, ActionForm form,HttpRequest req, HttpResponse res) throws Exception
      • Called by controller upon client request
      • One instance of each action class in an application
      • Developer must ensure thread safety of action class
      • Developer must overide method execute()
      • Each action class extends Action and overrides method execute().
      • No try/catch or InvalidLoginException
      • Struts uses declarative exception handling
      • Exceptions for actions are specfied in Struts configuration file
      • Action instances are invoked by the Struts framework from mappings specified in Action Mapping files that use URIs with a path attribute.
      • Returned View from an Action is specified by ActionForward return object.
        • Specifies destination after an Action has completed.
        • Declaritively specify action mapping with JSP and ActionForward in Application
        • Specify if it is a redirect with a flag
Using Data Transfer Objects (DTOs)
  • Course-grained view of remote fine-grained data.
  • Only data, no business logic
  • reduces network bandwidth and improves response times
  • Decouples business logic from presentation
  • maintenance and making enhancements is easier.
  • Collocation- Objects deployed in the same JVM
Struts View Componets
  • HTML, DTOs, ActionForms, JSPs, Custom Tags, Java Resource Bundles
Framework use of Action Forms for a Request
  • Check mapping to see if ActionForm is configured
  • If present, use action name to look up bean configuration
  • Check if action form created
  • Reuse if action form is created
  • Otherwise create new instance, store in appropriate scope as specified in action element.
  • Call reset()
  • Iterate request parameters , populate every param with Action form with action parameter
  • If validate is 'true' invoke validate.
  • Two important methods of Action form: reset() and validate()
  • reset() called by controller before populating ActionForm with request values.
  • Action form can reset its values back to default state.
  • Probably not to be used with multiple pages as values are not reset until an instance is destroyed.
  • Validate called after request values are inserted into ActionForm.
  • Must not be used for business operations- These are done in business objects only.
  • Validation is used for Presentation Validation only.
  • All ActionForms of application configued in form-beans section on Config File.
    • Configure Action forms
    • use form-bean names with one or more action elements.
    • DynaActionForm
      • New in Struts 1.1
      • org.apache.struts.action.DynaAction
  • JSP disadvantages
    • Developers may embed business logic in JSP
    • Learning curve
    • Container must recompile JSP when a change is made to a page.
  • Using Tag Libraries
      • Need to be registered in web.xml
      • Include taglib elements in JSP
      • <%@ taglib uri ="/...." prefix="bean">
      • No Java code, only HTML
  • Resource Bundles
    • Set on java.util.ResourceBundle
    • org.apache.struts.utils.MessageResources
  • Multiple App Support
    • Pre 1.1 versions- Only one struts-config.xml
    • 1.1 Many config files possible- developers may work in parallel.
    • Now called Application Modules

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