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Package Documentation for org.apache.commons.validator
The Validator package provides validation for JavaBeans based on an xml file.
Introduction
A common issue when receiving data either electronically or from
user input is verifying the integrity of the data. This work is
repetitive and becomes even more complicated when different sets
of validation rules need to be applied to the same set of data based
on locale for example. Error messages may also vary by locale.
This package attempts to address some of these issues and
speed development and maintenance of validation rules.
In order to use the Validator, the following basic steps are required:
- Create a new instance of the
org.apache.commons.validator.Validator class. Currently
Validator instances may be safely reused if the current ValidatorResources
are the same, as long as
you have completed any previous validation, and you do not try to utilize
a particular Validator instance from more than one thread at a time.
- Add any resources
needed to perform the validations. Such as the JavaBean to validate.
- Call the validate method on
org.apache.commons.validator.Validator.
Overview
The Commons Validator is a basic validation framework that
lets you define validation rules for a JavaBean in an xml file.
Validators, the validation definition, can also be defined in
the xml file. An example of a validator would be defining
what method and class will be called to perform the validation
for a required field. Validation rules can be grouped together
based on locale and a JavaBean/Form that the rules are associated
with. The framework has basic support for user defined constants
which can be used in some field attributes.
Validation rules can be defined in an xml file which keeps
them abstracted from JavaBean you are validating. The
property reference to a field supports nested properties
using the Apache Commons BeanUtils
(http://commons.apache.org/beanutils/) package.
Error messages and the arguments for error messages can be
associated with a fields validation.
Resources
After a Validator instance is created, instances of
classes can be added to it to be passed into
validation methods by calling the setParameter()
method. Below is a list of reserved parameters (class names).
Class Name
Validator Contstant
Description
java.lang.Object
Validator.BEAN_PARAM
JavaBean that is being validated
java.util.Locale
Validator.LOCALE_PARAM
Locale to use when retrieving a FormSet.
The default locale will be used if one
isn't specified.
org.apache.commons.validator.ValidatorAction
Validator.VALIDATOR_ACTION_PARAM
This is automatically added to a Validator's
resources as a validation is being processed.
If this class name is used when defining
a method signature for a pluggable validator,
the current ValidatorAction will be passed into
the validation method.
org.apache.commons.validator.Field
Validator.FIELD_PARAM
This is automatically added to a Validator's
resources as a validation is being processed.
If this class name is used when defining
a method signature for a pluggable validator,
the current Field will be passed into
the validation method.
Usage Example
This is a basic example setting up a required validator for
a name bean. This example is a working unit test (reference
org.apache.commons.validator.RequiredNameTest and
validator-name-required.xml located under validator/src/test).
Create an xml file with your validator and validation rules.
Setup your required validator in your xml file.
XML Example
Validator Example
Pluggable Validator Example
XML Example
Definition of a 'required' pluggable validator.
<form-validation>
<global>
<validator name="required"
classname="org.apache.commons.validator.TestValidator"
method="validateRequired"
methodParams="java.lang.Object, org.apache.commons.validator.Field"/>
</global>
<formset>
</formset>
</form-validation>
Add validation rules to require a first name and a last name.
<form-validation>
<global>
<validator name="required"
classname="org.apache.commons.validator.TestValidator"
method="validateRequired"
methodParams="java.lang.Object, org.apache.commons.validator.Field"/>
</global>
<formset>
<form name="nameForm">
<field property="firstName" depends="required">
<arg0 key="nameForm.firstname.displayname"/>
</field>
<field property="lastName" depends="required">
<arg0 key="nameForm.lastname.displayname"/>
</field>
</form>
</formset>
</form-validation>
Validator Example
Excerpts from org.apache.commons.validator.RequiredNameTest
InputStream in = this.getClass().getResourceAsStream("validator-name-required.xml");
// Create an instance of ValidatorResources to initialize from an xml file.
ValidatorResources resources = new ValidatorResources(in);
// Create bean to run test on.
Name name = new Name();
// Construct validator based on the loaded resources and the form key
Validator validator = new Validator(resources, "nameForm");
// add the name bean to the validator as a resource
// for the validations to be performed on.
validator.setParameter(Validator.BEAN_PARAM, name);
// Get results of the validation.
Map results = null;
// throws ValidatorException (catch clause not shown here)
results = validator.validate();
if (results.get("firstName") == null) {
// no error
} else {
// number of errors for first name
int errors = ((Integer)results.get("firstName")).intValue();
}
Pluggable Validator Example
Validation method defined in the 'required' pluggable validator
(excerpt from org.apache.commons.validator.TestValidator).
public static boolean validateRequired(Object bean, Field field) {
String value = ValidatorUtil.getValueAsString(bean, field.getProperty());
return GenericValidator.isBlankOrNull(value);
}