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Struts Validator Framework
This lesson introduces you the Struts Validator Framework.
In this lesson you will learn how to use Struts Validator Framework to
validate the user inputs on the client browser.
Introduction to Validator
Framework
Struts Framework provides the functionality to validate
the form data. It can be use to validate the data on the users browser as well
as on the server side. Struts Framework emits the java scripts and it can be
used to validate the form data on the client browser. Server side validation
of the form can be accomplished by sub classing your From Bean with
DynaValidatorForm class.
The Validator framework was developed by David Winterfeldt
as third-party add-on to Struts. Now the Validator framework is a part of
Jakarta Commons project and it can be used with or without Struts. The
Validator framework comes integrated with the Struts Framework and can be used
without doing any extra settings.
Using Validator
Framework
Validator uses the XML file to pickup the validation rules
to be applied to an form. In XML validation requirements are defined applied
to a form. In case we need special validation rules not provided by the
validator framework, we can plug in our own custom validations into
Validator.
The Validator Framework uses two XML configuration files
validator-rules.xml and validation.xml. The
validator-rules.xml defines the standard validation routines, these are
reusable and used in validation.xml. to define the form specific
validations. The validation.xml defines the validations applied to a
form bean.
Structure of
validator-rule.xml
The
validation-rules.xml is provided
with the Validator Framework and it declares and assigns the logical names to
the validation routines. It also contains the client-side javascript code for
each validation routine. The validation routines are java methods plugged into
the system to perform specific validations.
Following table contains the details of the elements in this file:
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Element
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Attributes and Description
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form-validation
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This is the root node. It contains nested elements
for all of the other configuration settings.
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global
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The validator details specified within this, are
global and are accessed by all forms.
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validator
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The validator element defines what validators
objects can be used with the fields referenced by the formset
elements.
The attributes are:
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name:
Contains a logical name for the validation routine
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classname:
Name of the Form Bean class that extends the subclass of
ActionForm class
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method:
Name of the method of the Form Bean class
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methodParams:
parameters passed to the method
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msg:Validator
uses Struts' Resource Bundle mechanism for externalizing error
messages. Instead of having hard-coded error messages in the
framework, Validator allows you to specify a key to a message in
the ApplicationResources.properties file that should be returned
if a validation fails. Each validation routine in the
validator-rules.xml file specifies an error message key as value
for this attribute.
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depends:
If validation is required, the value here is specified as
'required' for this attribute.
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jsFunctionName:
Name of the javascript function is specified here.
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javascript
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Contains the code of the javascript function used
for client-side validation. Starting in Struts 1.2.0 the default
javascript definitions have been consolidated to
commons-validator. The default can be overridden by supplying a
<javascript> element with a CDATA section, just as in struts
1.1.
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The Validator plug-in (validator-rules.xml) is supplied
with a predefined set of commonly used validation rules such as Required,
Minimum Length, Maximum length, Date Validation, Email Address validation
and more. This basic set of rules can also be extended with custom
validators if required.
Structure of validation.xml
This validation.xml configuration file defines
which validation routines that is used to validate Form Beans. You can
define validation logic for any number of Form Beans in this
configuration file. Inside that definition, you specify the validations you
want to apply to the Form Bean's fields. The definitions in this file use
the logical names of Form Beans from the struts-config.xml file along with
the logical names of validation routines from the validator-rules.xml file
to tie the two together.
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Element
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Attributes and Description
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form-validation
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This is the root node. It contains nested elements
for all of the other configuration settings
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global
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The constant details are specified in
<constant> element within this element.
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constant
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Constant properties are specified within this
element for pattern matching.
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constant-name
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Name of the constant property is specified
here
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constant-value
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Value of the constant property is specified
here.
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formset
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This element contains multiple <form>
elements
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form
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This element contains the form details.
The attributes
are:
name:Contains the form name.
Validator uses this logical name to map the validations to a Form Bean
defined in the struts-config.xml file
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field
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This element is inside the form element, and it
defines the validations to apply to specified Form Bean fields.
The attributes are:
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arg
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A key for the error message to be thrown incase
the validation fails, is specified here
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var
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Contains the variable names and their values as
nested elements within this element.
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var-name
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The name of the criteria against which a field is
validated is specified here as a variable
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var-value
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The value of the field is specified here
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Example of form in the
validation.xml
file:
<!-- An example form -->
<form name="logonForm">
<field property="username"
depends="required">
<arg key="logonForm.username"/>
</field>
<field property="password"
depends="required,mask">
<arg
key="logonForm.password"/>
<var>
<var-name>mask</var-name>
<var-value>^[0-9a-zA-Z]*$</var-value>
</var>
</field>
</form>
The <html:javascript> tag to allow front-end
validation based on the xml in validation.xml. For example the code:
<html:javascript formName="logonForm"
dynamicJavascript="true" staticJavascript="true"
/> generates the client side java script for
the form "logonForm" as defined in the validation.xml file. The
<html:javascript> when added in the jsp file generates the client site
validation script.
In the next lesson we will create a new form for
entering the address and enable the client side java script with the
Validator Framework.
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