WebSphere Application Server - IBM Redbooks

When a browser submits an HTML form, the Struts ActionServlet does the
following:
1. Looks at the field names from the HTML form
2. Matches them to the properties' names in the form bean
3. Automatically calls the setter methods of these variables to put the values
retrieved from the HTML form
The form bean can be used to collect data from the user, to validate what the
user entered, and by the JSP to repopulate the form fields
In the case of validation errors, Struts has a shared mechanism for raising and
displaying error messages. It automatically invokes the ActionForm.validate
method whenever the JSP page containing the form corresponding to this
ActionForm submits the form. Any type of validation can be performed in this
method. The only requirement is that it return a set of ActionError objects in the
return value. Each ActionError corresponds to a single validation failure, which
maps to a specific error message. These error messages are held in a properties
file to which the Struts application refers.
Custom tags
There are four tag libraries included in Struts:
1. The HTML tag library, which includes tags for describing dynamic pages,
especially forms.
2. The beans tag library, which provides additional tags for improved access to
Java beans and additional support for internationalization.
3. The logic tag library, which provides tags that support conditional execution
and looping.
4. The template tag library for producing and using common JSP templates in
multiple pages.
Using these custom tags, the Struts framework can automatically populate fields
to and from a form bean, providing two advantages:
► The only thing most JSPs need to know about the rest of the framework is the
proper field names and where to submit the form. The associated form bean
automatically receives the corresponding value.
► If a bean is present in the appropriate scope, for instance after an input
validation routine, the form fields will be automatically initialized with the
matching property values.
386 IBM WebSphere Application Server - Express V5.0.2 Developer Handbook