Learning Jakarta Struts, Part 2
Pages: 1, 2, 3
Determine the access path for each screen.
- The login screen will be the default application page.
- The welcome page will be accessed only upon a successful login by the user.
- The error page will be accessed from any page that can generate an error.
Define the ActionMappings that correlate to the application business logic
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Related Reading
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ActionMappings are basically the roadmap for the application. The
ActionMappings define what happens at any given point in an application.
ActionMappings are defined in the struts-config.xml file. ActionsMappings work
with forwards to provide the flow of the application.
Usually you build up ActionMapping information, such as the form name or
input, as you continue your development. Primarily, this development step is
meant to start forming the strawman of the struts-config.xml file. The forwards
for an action indicate what will happen when the action class returns one of the
defined MappingForwards. It is entirely possible to have many forwards available
to an action. Each action class can define specific forwards that are relevant
to that class. Also, keep in mind that it is possible to have global forwards.
Think of it as an include file for each action. If a returned forward is
not specific to the ActionMapping but is defined as a global forward, then
the global definition will be used. Local forwards can always be used to
override global forwards. In our sample below, if an "error" mapping is returned
from an action, then Errorpage.jsp will be displayed, even though that
forward is not specific to any action.
You will see as you continue your development that this config file can get
rather detailed in larger projects. In the sample below, taken from the
StrutsSample struts-config.xml file, we can see global forward definitions and a
sample action mapping. This mapping defines an action called "login" that is an
instance of the class com.oreilly.actions.LoginAction.
On a successful login the "success"
forward will display Welcome.jsp. If a "failure"
forward occurs, Login.jsp will be redisplayed. If an "error" forward is
returned, then the global forward will be used and display
Errorpage.jsp
<!-- ========== Global Forward Definitions -->
<global-forwards>
<forward name="login" path="/Login.jsp"/>
<forward name="error" path="/Errorpage.jsp"/>
</global-forwards>
<!-- ========== Action Mapping Definitions -->
<action-mappings>
<!-- Attributes of the <action> element -->
<!--
For other available attributes see the JavaDocs for
org.apache.struts.action.ActionMapping
path - The request URI path that is matched to select
this mapping.
type - Fully qualified Java class name of the
Action implementation class used by this mapping.
name - The name of the form bean defined in the
config file that this action will use.
unknown - Set to true if this action should be
configured as the default for this application to handle
all requests not handled by another action. Only one
action can be defined as a default within a single
application.
scope - Identifier of the scope ("request" or "session"
within which the form bean, if any, associated with this
action will be created
input - Context-relative path of the input form to which
control should be returned if a validation error is
encountered.
validate - Set to true if the validate() method of the
action associated with this mapping should be called.
forward elements - The set of ActionForwards locally
associated with this mapping.
-->
<!-- =================== -->
<!-- O'Reilly Struts Sample Main Actions -->
<!-- =================== -->
<action path="/login"
type="com.oreilly.actions.LoginAction"
name="loginForm"
scope="request"
input="/Login.jsp">
<forward name="success" path="/Welcome.jsp"/>
<forward name="failure" path="/Login.jsp"/>
</action>
</action-mappings>As we have already talked about in the first article, struts-config.xml is the
controller in the MVC model. It is well worth spending development time on this
step to make sure your actions match your application requirements. Once all the pieces come into place, you will want to avoid a situation where you have to completely reorganize your actions due to poor definition at the beginning of the project.
Our StrutsSample application requires only one action -- the login. Depending on the size of your application, there can be many actions required and defined. Once the ActionMappings are defined, you can go through each one and start putting together the ActionMapping classes and form classes.
