Configuring Struts Components

1
Configuring Struts Components

• web.xml
• The web application deployment descriptor
  required by Java Servlet specification.
• struts-config.xml
• frameworks deployment descriptor. It is used to
  load and configure various components used by
  struts framework.
• application.properties
• Provides message resources to struts based web
  application

2
The web application deployment descriptor

• Struts framework includes two components that
  need to be configured through web.xml file the
  ActionServlet and optionally, tag libraries.
• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE web-app PUBLIC "-//Sun Microsystems,
  Inc.//DTD Web Application 2.3//EN"
  "http//java.sun.com/dtd/web-app_2_3.dtd"gt
• ltweb-app id"WebApp"gt
• ltdisplay-namegtPRO617Weblt/display-namegt
• ltservletgt
• ltservlet-namegtactionlt/servlet-namegtlt!- only one
  action servlet per application --gt
• ltservlet-classgtorg.apache.struts.action.ActionServ
  letlt/servlet-classgt
• ltinit-paramgt
• ltparam-namegtconfiglt/param-namegtlt! context
  relative path to xml resource containing config
  info --gt
• ltparam-valuegtWEB-INF/struts-config.xmllt/param-valu
  egt
• lt/init-paramgt
• ltinit-paramgt
• ltparam-namegtdebuglt/param-namegtlt!- debug level
  for this servlet 0 least serious, 6 most
  serious --gt
• ltparam-valuegt2lt/param-valuegt
• lt/init-paramgt
• ltinit-paramgt
• ltparam-namegtdetaillt/param-namegtlt!- debug level
  for Digester to process application config files
  0 to 6 -- gt
• ltparam-valuegt2lt/param-valuegt

3
struts-config.xml file

• Struts config file is a living blueprint of
  application
• Struts configuration and Action Servlet work
  together to form a control layer
• Every component in Struts configuration is a Java
  object
• Struts framework use reflection and introspection
  to automate loading and configuring java objects
• Struts config file helps your application react
  to changes quickly with minimal effort.
• In practice, it is separating things that rarely
  change the underlying java classes from things
  that often change the java objects deployed at
  runtime. Principle of protected variationLarman
• Example file
• ltstruts-configgt
• lt!-- Data Sources --gt
• ltdata-sourcesgt
• lt/data-sourcesgt
• lt!-- Form Beans --gt
• ltform-beansgt
• lt/form-beansgt
• lt!-- Global Exceptions --gt
• ltglobal-exceptionsgt
• lt/global-exceptionsgt
• lt!-- Global Forwards --gt
• ltglobal-forwardsgt

4
Struts configuration elements

• Data-sources Element
• Contains zero or more data-source element
• lt!ELEMENT data-sources (data-source)gt
• Data-source Element
• lt!ELEMENT data-source (set-property)gt
• Acts as a factory for database connections and
  provides a single point of control
• set-property allows to configure properties that
  are specific to data source implementation
• Example
• ltdata-sourcesgt
• ltdata-sourcegt
• ltset-property property"driverClass" value""/gt
• ltset-property property"user" value""/gt
• ltset-property property"password" value""/gt
• ltset-property property"url" value""/gt
• lt/data-sourcegt
• lt/data-sourcesgt
• Form-Beans Element
• Configures multiple ActionForm classes that are
  used by views
• Within form-beans you can configure zero or more
  form bean child elements

5
Struts Configuration Elements

• Global forwards element
• Logical name for forwarding or redirecting to a
  view.
• The forward element maps a logical name to an
  application relative URI
• Hard coding of literal URI is avoided using
  forward element
• Example
• ltglobal-forwardsgt
• ltforward nameloginForward
  path/jsp/login.jsp redirecttruegt
• lt/global-forwardsgt
• Message resources element
• Specifies characteristics of the message resource
  bundles that contain the localized messages for
  an application.
• Each struts-config file can define one or more
  message resource bundles
• E.g. ltmessage-resources parameter"pro617web.resou
  rces.ApplicationResources"/gt
• Typically, the bundles are either in a jar file
  or under WEB-INF/classes folder
• Plug-in element
• Specifies a fully qualified class name of a
  general purpose application plug-in module that
  receives notification of application startup and
  shutdown events.
• Plug-in element may contain zero or more
  set-property elements, so that extra
  configuration information may be passed to Plugin
  class
• E.g.
• ltplug-in className"org.apache.struts.tiles.TilesP
  lugin"gt
• ltset-property property"" value""/gt

6
Struts Configuration Elements

• Action-mappings Element
• Contains a set of zero or more action elements
  for Struts application
• Action element describes a mapping from a
  specific request path to a corresponding action
  class
• Controller selects a particular mapping by
  matching a URI path in the request with the path
  attribute in one of the action elements
• E.g.
• ltaction path/signin typecom.actions.LoginAct
  ion scoperequest nameloginForm
  validatetrue input/jsp/login.jspgt
• ltforward nameSuccess pathjsp/login.jsp /gt
• ltforward nameFailure pathjsp/invalidlogin.j
  sp /gt
• lt/actiongt
• Path attribute, in other words is the name of the
  action. It is the application relative path to
  the submitted request, starting with a /
  character and without filename extension
• Scope is the scope in which form bean is placed
  either request or session. Default value is
  session. It is specified only when name attribute
  is specified.
• Name is the name of the form bean element as
  specified in the form beams element
• Validate attribute determines if validate method
  of ActionForm is called before invoking execute
  method of the action class
• Type is the type of the action class
• Unknown attribute determines whether this action
  should be configured as the default for this
  application. It is optional and default is false

7
The application resources file

• Capable and flexible messaging system.
• Text for the messages is stored in this
  properties file.
• In java an jsp code, a key for the message is
  given the text of the message is retrieved from
  the properties file at runtime.
• If you want to localize your application, you can
  include additional application resources file for
  the locales you would like to support.
• The application name is only a convention. There
  is no framework default.

8
ActionForms

• ActionForms are versatile objects that play the
  role of field harvester, data butter, type
  transformer and transfer object all within the
  span of a single request.
• ActionForm as field harvester
• To harvest request parameters, all the Struts
  developers needs to do is provide an ActionForm
  with JavaBean properties that match the names of
  HTTP parameters. The rest is automatic
• ActionForm as data buffer
• ActionForm fields are not the destination of the
  input, but a buffer to be validated before the
  input is committed.
• ActionForm as a data validator
• Prima facie validation of property values and
  type
• ActionForm as a type transformer
• Helper methods could be included on ActionForms
  to help with type conversions and
  transformations.
• ActionForm as a transfer object
• An ActionForm is a carrier for data to be used by
  another bean or process.

9
ActionClass

• Action objects does the actual work.
• Actions are multithreaded.
• There is a single instance of any given Action
  subclass per application.
• General Responsibilities
• Validate preconditions
• Call any needed business logic methods
• Detect any other processing errors
• Route control to the appropriate view
• It is an adaptor between HTTP and the rest of the
  application. This way it provides means for
  simpler, broader, flexible and a robust design
• The standard Actions
• DispatchAction
• Action class to handle several related tasks
• Keeping related operations together simplifies
  maintenance and flow control
• LookupDispatchAction
• A convenient way to select a dispatch method in
  case of multiple submit.