Package Documentation for org.apache.commons.validator

The Validator package provides validation for JavaBeans based on an xml file.
[Dependencies] [Introduction] [Overview] [Resources] [Usage Example]

### 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,
// but aren't catching for example
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);
}