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Struts provides client side validation(using JavaScript) for a few validators. Using AJAX validation, all validators available to the application on the server side can be used without forcing the page to reload, just to show validation errors. AJAX validation has a server side, which is in included in JSON Plugin (an interceptor and a result). Client side must be handled by applictions themself. One reason for that is there are too many JavaScript frameworks and libraries. Struts has no preference which of them you use. Previous versions of Struts included a client side which was relying on the Dojo JS framework and was located in Struts Dojo plugin. That has been deprecated for a long time and was eventually removed.


This example is taken from the Struts showcase application.

Create the action class

public class AjaxFormSubmitAction extends ActionSupport {
    private String requiredValidatorField = null;
    private String requiredStringValidatorField = null;
    private Integer integerValidatorField = null;
    private Date dateValidatorField = null;
    private String emailValidatorField = null;
    private String urlValidatorField = null;
    private String stringLengthValidatorField = null;
    private String regexValidatorField = null;
    private String fieldExpressionValidatorField = null;
    public void validate() {
        if (hasFieldErrors()) {
            addActionError("Errors present!");
    public Date getDateValidatorField() {
        return dateValidatorField;
        message="must be a min 01-01-1990 max 01-01-2000 if supplied")
    public void setDateValidatorField(Date dateValidatorField) {
        this.dateValidatorField = dateValidatorField;
    public String getEmailValidatorField() {
        return emailValidatorField;
    @EmailValidator(message="must be a valid email if supplied")
    public void setEmailValidatorField(String emailValidatorField) {
        this.emailValidatorField = emailValidatorField;
    public Integer getIntegerValidatorField() {
        return integerValidatorField;
    @IntRangeFieldValidator(min="1", max="10", message="must be integer min 1 max 10 if supplied")
    public void setIntegerValidatorField(Integer integerValidatorField) {
        this.integerValidatorField = integerValidatorField;
    public String getRegexValidatorField() {
        return regexValidatorField;
        message="regexValidatorField must match a regexp (.*\\.txt) if specified")
    public void setRegexValidatorField(String regexValidatorField) {
        this.regexValidatorField = regexValidatorField;
    public String getRequiredStringValidatorField() {
        return requiredStringValidatorField;
    @RequiredStringValidator(trim=true, message="required and must be string")
    public void setRequiredStringValidatorField(String requiredStringValidatorField) {
        this.requiredStringValidatorField = requiredStringValidatorField;
    public String getRequiredValidatorField() {
        return requiredValidatorField;
    public void setRequiredValidatorField(String requiredValidatorField) {
        this.requiredValidatorField = requiredValidatorField;
    public String getStringLengthValidatorField() {
        return stringLengthValidatorField;
        message="must be a String of a specific greater than 1 less than 5 if specified")
    public void setStringLengthValidatorField(String stringLengthValidatorField) {
        this.stringLengthValidatorField = stringLengthValidatorField;
    public String getFieldExpressionValidatorField() {
        return fieldExpressionValidatorField;
        expression = "(fieldExpressionValidatorField == requiredValidatorField)", 
        message = "must be the same as the Required Validator Field if specified")
    public void setFieldExpressionValidatorField(
            String fieldExpressionValidatorField) {
        this.fieldExpressionValidatorField = fieldExpressionValidatorField;
    public String getUrlValidatorField() {
        return urlValidatorField;
    @UrlValidator(message="must be a valid url if supplied")
    public void setUrlValidatorField(String urlValidatorField) {
        this.urlValidatorField = urlValidatorField;


Map the Action

Note that is is not necessary when using Convention Plugin.

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd">
         <action name="ajaxFormSubmit" class="org.apache.struts2.showcase.validation.AjaxFormSubmitAction">
             <interceptor-ref name="jsonValidationWorkflowStack"/>
             <result name="input">/WEB-INF/validation/ajaxFormSubmit.jsp</result>
             <result type="jsonActionRedirect">ajaxFormSubmitSuccess</result>

AJAX validation is performed by the jsonValidation interceptor. This interceptor is included in the jsonValidationWorkflowStack, and is required in order to perform AJAX validation. Normal results(input, success, etc) should be provided for the action in the case that someone tries to access the action directly, in which case normal validation will be triggered. So, how does the jsonValidation know that it must perform AJAX validation vs regular validation? We will see that in a minute, but you don't need to know that in order to use AJAX validation. Same applies for specialized Redirect Result Type jsonActionRedirect.

Create the JSP

<%@taglib prefix="s" uri="/struts-tags" %>
    <title>Struts2 Showcase - Validation - AJAX Form Submit</title>
    <s:head theme="xhtml"/>
<div class="page-header">
    <h1>AJAX Form Submit</h1>
    <h3>Action Errors Will Appear Here</h3>
    <s:actionerror theme="ajaxErrorContainers"/>
    <s:form method="POST" theme="xhtml">
        <s:textfield label="Required Validator Field" name="requiredValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Required String Validator Field" name="requiredStringValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Integer Validator Field" name="integerValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Date Validator Field" name="dateValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Email Validator Field" name="emailValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="URL Validator Field" name="urlValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="String Length Validator Field" name="stringLengthValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Regex Validator Field" name="regexValidatorField" theme="ajaxErrorContainers"/>
        <s:textfield label="Field Expression Validator Field" name="fieldExpressionValidatorField" theme="ajaxErrorContainers"/>
        <s:submit label="Submit" cssClass="btn btn-primary"/>

Things to note on this JSP:

  • The form tag does not have validate set to true, which would perform client validation before the AJAX validation.
  • It uses a customized theme ajaxErrorContainers. The default Struts themes generate HTML-Elements to show validation errors only if errors are present when page is created on server side. But in order to show validation errors that arrive later via AJAX it is necessary to have error-container elements in DOM always.

What happens if validation succeeds? That depends on your request parameters and action configuration. If you are using jsonActionRedirect result mentioned above the action will be executed while AJAX request is active and respond with JSON providing a new URL to load. Otherwise the AJAX response will be empty and the form must be submitted a 2nd time but as usual request, not AJAX.

Setting validate to true in the form tag will enable client side, JavaScript validation, which can be used along with AJAX validation (runs before the AJAX validation).

Custom Theme

In this sample the custom theme is based on xhtml theme. It is required to override 3 FTL files.

parent = xhtml


    Make sure element is always present. To be filled later via JS.
<#if parameters.id??>
<#if parameters.cssClass??>
<#if parameters.cssStyle??>
<#if (actionErrors?? && actionErrors?size > 0)>
    <#list actionErrors as error>
        <#if error??>
            <li><span><#if parameters.escape>${error!?html}<#else>${error!}</#if></span><#rt/></li><#rt/>


<#if (parameters.errorposition!"top") == 'bottom'>
<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors[parameters.name]??/>
<#if hasFieldErrors>
<tr errorFor="${parameters.id}">
    <td class="tdErrorMessage" colspan="2"><#rt/>
        <#if hasFieldErrors>
            <#list fieldErrors[parameters.name] as error>
                <div class="errorMessage">${error?html}</div><#t/>


    Always include elements to show errors. They may be filled later via AJAX.
<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors[parameters.name]??/>
<#if (parameters.errorposition!"top") == 'top'>
<tr errorFor="${parameters.id}">
    <td class="tdErrorMessage" colspan="2" data-error-for-fieldname="${parameters.name}"><#rt/>
        <#if hasFieldErrors>
            <#list fieldErrors[parameters.name] as error>
                <div class="errorMessage">${error?html}</div><#t/>
<#if !parameters.labelposition?? && (parameters.form.labelposition)??>
<#assign labelpos = parameters.form.labelposition/>
<#elseif parameters.labelposition??>
<#assign labelpos = parameters.labelposition/>
    if the label position is top,
    then give the label it's own row in the table
<#if (labelpos!"") == 'top'>
    <td class="tdLabelTop" colspan="2"><#rt/>
    <td class="tdLabel"><#rt/>
<#if parameters.label??>
    <label <#t/>
<#if parameters.id??>
        for="${parameters.id?html}" <#t/>
<#if hasFieldErrors>
<#if parameters.required!false && parameters.requiredPosition!"right" != 'right'>
        <span class="required">*</span><#t/>
<#if parameters.required!false && parameters.requiredPosition!"right" == 'right'>
 <span class="required">*</span><#t/>
<#include "/${parameters.templateDir}/${parameters.expandTheme}/tooltip.ftl" />
<#-- add the extra row -->
<#if (labelpos!"") == 'top'>


To show users some nice visual feedback while waiting for AJAX response you can use a little CSS. Remember to include the referenced indicator.gif.

.ajaxVisualFeedback {
    width: 16px;
    height: 16px;
    background-image: url('../images/indicator.gif');
    background-repeat: no-repeat;
    float: right;



Now this is where the magic happens. Here jQuery is used to register an eventhandler which intercepts form submits. It takes care of hiding validation errors that might be present, submit the form via AJAX and handle JSON responses.

  * Validates form per AJAX. To be called as onSubmit handler.
  * @param event onSubmit event
function ajaxFormValidation(event) {
    var _form = $(event.target);
    var _formData = _form.serialize(true);
    // prepare visual feedback
    // you may want to use other elements here
    var originalButton = _form.find('.btn-primary');
    // note: jQuery returns an array-like object
    if (originalButton && originalButton.length && originalButton.length > 0) {
        var feedbackElement = $('<div class="ajaxVisualFeedback"></div>').insertAfter(originalButton);
        var restoreFunction = function() {
    var options = {
        data: 'struts.enableJSONValidation=true&struts.validateOnly=false&' + _formData,
        async: true,
        processData: false,
        type: 'POST',
        success: function (response, statusText, xhr) {
            if (response.location) {
                // no validation errors
                // action has been executed and sent a redirect URL wrapped as JSON
                // cannot use a normal http-redirect (status-code 3xx) as this would be followed by browsers and would not be available here
                // follow JSON-redirect
                window.location.href = response.location;
            } else {
                if (restoreFunction) {
                _handleValidationResult(_form, response);
        error: function(xhr, textStatus, errorThrown) {
            if (restoreFunction) {
            // show user an error message
            _handleValidationResult(_form, {errors: ['Network or server error!']})
    // send request, after delay to make sure everybody notices the visual feedback :)
    window.setTimeout(function() {
        var url = _form[0].action;
        jQuery.ajax(url, options);
    }, 1000);
 * Removes validation errors from HTML DOM.
function _removeValidationErrors() {
    // action errors
    // you might want to use a custom ID here
    $('ul.errorMessage li').remove();
    // field errors
 * Incorporates validation errors in HTML DOM.
 * @param form Form containing errors.
 * @param errors Errors from server.
function _handleValidationResult(form, errors) {
    // action errors
    if (errors.errors) {
        // you might want to use a custom ID here
        var errorContainer = $('ul.errorMessage');
        $.each(errors.errors, function(index, errorMsg) {
            var li = $('<li><span></span></li>');
            li.text(errorMsg); // use text() for security reasons
    // field errors
    if (errors.fieldErrors) {
        $.each(errors.fieldErrors, function(fieldName, errorMsg) {
            var td = $('td[data-error-for-fieldname="' + fieldName + '"]');
            if (td) {
                var div = $('<div class="errorMessage"></div>');
                div.text(errorMsg); // use text() for security reasons
// register onSubmit handler
$(window).bind('load', function() {
    $('form').bind('submit', ajaxFormValidation);


How it works

jsonValidation interceptor must be placed on a stack, following the validation interceptor. The interceptor itself won't perform any validation, but will check for validation errors on the action being invoked (assuming that the action is ValidationAware).

If you just want to use AJAX validation, without knowing the implementation details, you can skip this section.

When the jsonValidation interceptor is invoked, it will look for a parameter named struts.enableJSONValidation, this parameter must be set to true, otherwise the interceptor won't do anything. Then the interceptor will look for a parameter named struts.validateOnly, if this parameter exists, is set to true, and there are validation errors (o action errors) they will be serialized into JSON in the form:

    "errors": ["Global Error 1", "Global Error 2"],
    "fieldErrors": {
        "field1": ["Field 1 Error 1", "Field 1 Error 2"],
        "field1": ["Field 2 Error 1", "Field 2 Error 2"]  

If the action implements the ModelDrive interface, "model." will be stripped from the field names in the returned JSON. If validation succeeds (and struts.validateOnly is true), an empty JSON string will be returned:


If struts.validateOnly is false the action and result are executed. In this case jsonActionRedirect result is very useful. It creates a JSON response in the form:

{"location": "<url to be loaded next>"}

Remember to set struts.enableJSONValidation=true in the request to enable AJAX validation

JSONValidationInterceptor parameters

The following request parameters can be used to enable exposing validation errors:

  • struts.enableJSONValidation - a request parameter must be set to true to use this interceptor
  • struts.validateOnly - If the request has this parameter, execution will return after validation (action won't be executed). If struts.validateOnly is set to false you may want to use JSONActionRedirectResult
  • struts.JSONValidation.no.encoding - If the request has this parameter set to true, the character encoding will NOT be set on the response - is needed in portlet environment

You can override names of these parameters by specifying the following parameters when setting up a stack:

  • validateJsonParam - to override name of struts.enableJSONValidation
  • validateOnlyParam - to override name of struts.validateOnly
  • noEncodingSetParam - to override name of struts.JSONValidation.no.encoding
  • validationFailedStatus - status to be set on response when there are validation errors, by default 400

 Parameters overriding is available since Struts 2.5.9

Flow chart of AJAX validation

Some details are omitted, like results used.

As explained above: there is a case where form is submitted twice, one time as AJAX with validation only and another time as usual submit.