Validating text tag
Types of validation
This extension adds the jsp tag "valtext" to the struts framework.
The valtext tag extends the struts text tag by a functionality to pre-validate
the user's input.
Pre-validation starts from the concept that the validation of
user input falls into two classes:
- presentation related and
- business logic related
validations.
This differentiation corresponds to the model and the view of the MVC paradigm.
- A presentation related validation is for example that a numeric field
contains no alphabetic characters.
- A business logic related validation is that adult persons are 18 years old or
older.
While business logic-related validations are handled in the Action
and ActionForm classes,
presentation-related validation should take place even before the
ActionForm beans are populated.
Type conversions
Due to the nature of web-sites all user-input in text field is regarded as
a String, even if it represents a number or a date.
If the property in the corresponding bean has a type other than String,
the user input must be converted to the type of the property, for example
an Integer.
The struts framework delegates the type conversion to the "commons beanutils"
project which allows for the installation of customized conversion methods
but not for input tag specific conversion.
It may be for example that the property in a bean is a Timestamp, but that
on the web page for whatever reason only the date part of the timestamp
is displayed and accepted as input.
The valtext tag allows to define the format in which a property is displayed
on the screen.
The same format is also used to validate the user's input.
The format is described by the formatClass, the pattern and the locale
taken from the header of the HttpRequest.
In order to avoid tedious typing of full class names of the format class
logical names may be used for the format classes.
An object of type FormatSource translates the logical names to the
full class names and also defines how the pattern and the locale go into
the resulting format.
Parameter description
- required
- Specifies, if the input is obligatory or not.
Allowed values are
true, false, yes
and no.
- formatClass
- Specifies the type of the format.
By default
number and date can be used.
They create an instance of DecimalFormat and
SimpleDateFormat respectively.
- pattern
- Defines the pattern of the format
- errorName
- If an error is generated its text is read from
the resources file specified. This name is either
- error.required.errorName or
- error.format.errorName.
If no errorName is specified, the name of the property is used.
Implementation
When the valtext tag is processed, the four additional parameters are
concatenated to a single string seperated by underscores.
This string is stored in the form in a hidden input field with the name
"valInfo." + the name of the property.
When the user submits the form the contents of the hidden field are sent
to the action servlet.
The processPopulate method of the ActionServlet is overwritten
by a method that calls the validation method before populating the associated
bean.
Installation
- Include the file valtext.jar in the libpath.
- Add the val-taglib.tld file in the WebInf directory.
- Replace the servlet-class parameter of the action servlet
in the file web.xml by "com.db.ta.services.formval.ValActionServlet".
- In the jsp-files add a line like
<%@ taglib uri="/WEB-INF/val-taglib.tld" prefix="valt" %>
-
Use the tag. For example
<valt:valtext property="amount" size="12" pattern="###0.00"/>
-
Add all necessary error messages to the resource file like
error.required.amount=Please enter a value for amount.