English: Logo of Apache Struts

Apache Struts has changed the way we develop a Web application. Since its inception as an MVC architecture, Struts has been extensively used in J2EE world to develop robust, extendable and effective web applications.

Introduction to Struts Validation Framework

One of the important features of Struts framework is Struts Validation framework that performs validation on incoming form data. Validation framework was introduced by David Winterfeldt as an external plugin to Struts framework. It’s functionality has since been split so that validator can serve as the basis for a independant component and is now part of Jakarta Commons.

The Struts framework’s simple validation interface alleviates much of the headache associated with handling data validation, allowing you to focus on validation code and not on the mechanics of capturing data and redisplaying incomplete or invalid data.

In order to do form validation without Validator framework, one has to use validate() method of the form bean (ActionForm class) to perform this task. Also one has to handle error messages during manual validation. Lot of fields that we validate require same logic to validate them, hence code is unneccessarily duplicated (if not managed properly).

Validation framework comes with set of useful routines to handle form validation automatically and it can handle both server side as well as client side form validation. If certain validation is not present, you can create your own validation logic and plug it into validation framework as a re-usable component.

Validator uses two XML configuration files to determine which validation routines should be installed and how they should be applied for a given application, respectively. The first configuration file, validator-rules.xml, declares the validation routines that should be plugged into the framework and provides logical names for each of the validations. The validator-rules.xml file also defines client-side JavaScript code for each validation routine. Validator can be configured to send this JavaScript code to the browser so that validations are performed on the client side as well as on the server side.

The second configuration file, validation.xml, defines which validation routines should be applied to which Form Beans. 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.

Using the Validator framework involves enabling the Validator plug-in, configuring Validator’s two configuration files, and creating Form Beans that extend the Validator’s ActionForm subclasses. The following sections explain in detail how to configure and use Validator.

Create a Struts project

Create a struts web application project. I assume you have working environment set for a Struts project. If not then go through the tutorial: Creating Struts application using Eclipse and create a struts project.

Create Form Beans

struts validator form bean
Create a form bean in your project called CustomerForm and copy following code in it.

package net.viralpatel.struts.validation.form;
import org.apache.struts.validator.ValidatorForm;
public class CustomerForm extends ValidatorForm {
    private String name;
    private String telephone;
    private String email;
    private int age;
    public String getName() {
        return name;
    public void setName(String name) {
        this.name = name;
    public String getTelephone() {
        return telephone;
    public void setTelephone(String telephone) {
        this.telephone = telephone;
    public String getEmail() {
        return email;
    public void setEmail(String email) {
        this.email = email;
    public int getAge() {
        return age;
    public void setAge(int age) {
        this.age = age;

We will use this validator plugin to validate this form. Note that the form bean is extended from class ValidatorForm and not ActionForm as we generally do in Struts project.

Add Validator Plug-in in struts-config.xml

In order to use Validator in our project we need to configure it in struts-config.xml file. For this add following code in your struts-config.xml file.

<!-- Validator Configuration -->
<plug-in className="org.apache.struts.validator.ValidatorPlugIn">
    <set-property property="pathnames"
                /WEB-INF/validation.xml" />

This definition tells Struts to load and initialize the Validator plug-in for your application. Upon initialization, the plug-in loads the comma-delimited list of Validator config files specified by the pathnames property. Each config file’s path should be specified by use of a Web application-relative path, as shown in the previous example.

Define validations for the form

validation.xml file struts validator framework

Create a file validation.xml in your applications WEB-INF directory. And copy following content in it.

<?xml version="1.0" encoding="UTF-8" ?>
<!--DOCTYPE form-validation PUBLIC
          "-//Apache Software Foundation//DTD Commons Validator Rules Configuration 1.1.3//EN"
    <form name="CustomerForm">
        <field property="name" depends="required">
            <arg key="label.name" />
        <field property="age" depends="required, integer, intRange">
            <arg0 key="label.age" />
            <arg1 key="${var:min}" resource="false"/>
            <arg2 key="${var:max}" resource="false"/>
        <field property="telephone" depends="required, mask">
            <arg key="label.telephone" />
            <arg1 key="label.telephone" />
        <field property="email" depends="email">
            <arg0 key="label.email" />
            <arg1 key="label.email" />

In the above xml file, we have defined the rules for form validation. Note that we are validating form CustomerForm and the fields being validated are name, age, telephone and email. tag defines the validation for a property of form. We can specify different rules like required, integer, email, intRange, mask etc in depends attribute of field tag..

Also you can define constants that can be reused in the validation xml using global constants tag.

Struts-config.xml entry for the action

Following is the entry in struts-config.xml file which maps the Action to our Validator form.

    <form-bean name="CustomerForm"
        type="net.viralpatel.struts.validation.form.CustomerForm" />
    <action path="/customer" name="CustomerForm" validate="true"
        <forward name="success" path="/Customer.jsp" />
        <forward name="failure" path="/index.jsp" />

Configuring ApplicationResources.properties

Struts validation framework uses externalization of the error messages. The messages are stored in a property file (ApplicationResource.properties) and are referred by the key values. Copy following in your ApplicationResource.properties (or MessageResource.properties).

label.name= Name
label.email= Email
label.telephone= Telephone
label.age= Age
# general error msgs
errors.header=<font size="2"><UL>
errors.prefix=<LI><span style="color: red">
errors.invalid={0} is invalid.
errors.maxlength={0} can not be greater than {1} characters.
errors.minlength={0} can not be less than {1} characters.
errors.range={0} is not in the range {1} through {2}.
errors.required={0} is required.
errors.byte={0} must be an byte.
errors.date={0} is not a date.
errors.double={0} must be an double.
errors.float={0} must be an float.
errors.integer={0} must be an integer.
errors.long={0} must be an long.
errors.short={0} must be an short.

Create JSP to display the form

Create a JSP file called index.jsp and copy following content in it.

<%@ taglib uri="http://struts.apache.org/tags-html" prefix="html"%>
<%@ taglib uri="http://struts.apache.org/tags-bean" prefix="bean"%>
<title>Struts Validation Framework example.</title>
<html:errors />
<html:javascript formName="CustomerForm" />
<html:form action="/customer">
    <bean:message key="label.name" />
    <html:text property="name"></html:text>
    <br />
    <bean:message key="label.age" />
    <html:text property="age"></html:text>
    <br />
    <bean:message key="label.email" />
    <html:text property="email"></html:text>
    <br />
    <bean:message key="label.telephone" />
    <html:text property="telephone"></html:text>
    <br />
    <html:submit value="Submit"></html:submit>

Running the application

We are done with our application. Now execute it from any web container (Tomcat in my case) and open in browser.
struts validator form screen

Enter any invalid value in the form and press submit.


Reference :http://viralpatel.net


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