dwr reverse ajax stock demo application

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I am implementing a dwr reverse ajax example given here

http://wiki.netbeans.org/CreateReverseAjaxWebAppsWithDWR

below is the code

index.jsp fetches the values from StocksDemo.java

index.jsp

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
        <title>DWR StocksDemo</title>


        <%-- This files are created in the runtime --%>
        <script type='text/javascript' src='${pageContext.request.contextPath}/dwr/util.js'></script>        
        <script type='text/javascript' src='${pageContext.request.contextPath}/dwr/interface/StocksDemo.js'></script>
        <script type='text/javascript' src='${pageContext.request.contextPath}/dwr/engine.js'></script>


        <script type="text/javascript">
            function getStocks() {
                StocksDemo.sendStocks();
            }
        </script>        

        <link rel="stylesheet" type="text/css" href="generic.css" /> 
    </head>

    <body onload="dwr.engine.setActiveReverseAjax(true);">


        <h1>Receiving Stock Rates using Reverse Ajax</h1>

        <p>The following example illustrates how stock rates can be pushed from the server. Note: these are faked rates. A real application would use something like a Reuters live stockfeed at the back-end.</p>
        <input type="button" value="Get Stocks" onclick="getStocks()"/>
        <hr>

        <table style="width:500px" border="0" cellpadding="0">
            <tr>
                <td class="headName" ><b>Name</b></td>
                <td class="headValue" ><b>value</b></td>
            </tr>
            <tr><td>Allianz SE</td><td><div id="allianz">wait...</div></td></tr>
            <tr><td>Bayer AG</td><td><div id="bayer">wait...</div></td></tr>
            <tr><td>BMW AG St</td><td><div id="bmw">wait...</div></td></tr>
            <tr><td>Commerzbank AG</td><td><div id="commerzbank">wait...</div></td></tr>
            <tr><td>Daimler AG</td><td><div id="daimler">wait...</div></td></tr>
            <tr><td>Deutsche Bank AG</td><td><div id="deutschebank">wait...</div></td></tr>
            <tr><td>Deutsche Post AG</td><td><div id="deutschepost">wait...</div></td></tr>
            <tr><td>Deutsche Telekom AG</td><td><div id="telekom">wait...</div></td></tr>
            <tr><td>Hypo Real Estate Holding AG</td><td><div id="hypo">wait...</div></td></tr>
            <tr><td>Infineon Technologies AG</td><td><div id="infineon">wait...</div></td></tr>
            <tr><td>Linde AG</td><td><div id="linde">wait...</div></td></tr>
            <tr><td>METRO AG St</td><td><div id="metro">wait...</div></td></tr>
            <tr><td>RWE AG St</td><td><div id="rwe">wait...</div></td></tr>
            <tr><td>SAP AG</td><td><div id="sap">wait...</div></td></tr>
            <tr><td>Siemens AG</td><td><div id="siemens">wait...</div></td></tr>
            <tr><td>TUI AG</td><td><div id="tui">wait...</div></td></tr>
            <tr><td>Volkswagen AG St</td><td><div id="vw">wait...</div></td></tr> 
        </table>  

        <br>
    </body>
</html> 

my pojo classe

StocksDemo.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.proxy.dwr.Util;
import org.directwebremoting.util.Logger;

/**
 * Reverse Ajax class.
 * 
 * @author Siegfried Bolz (blog.jdevelop.eu)
 */
public class StocksDemo {

    protected static final Logger log = Logger.getLogger(StocksDemo.class);

    private List<StocksBean> stocks = new ArrayList<StocksBean>();


    /**
     * Initialize the stocklist with values.
     */
    public StocksDemo() {
        stocks.add(new StocksBean("bmw", "36.55"));
        stocks.add(new StocksBean("linde", "91.01"));
        stocks.add(new StocksBean("commerzbank", "22.59"));
        stocks.add(new StocksBean("infineon", "5.07"));
        stocks.add(new StocksBean("siemens", "71.77"));
        stocks.add(new StocksBean("sap", "31.61"));
        stocks.add(new StocksBean("bayer", "51.29"));
        stocks.add(new StocksBean("metro", "52.70"));
        stocks.add(new StocksBean("tui", "16.96"));
        stocks.add(new StocksBean("daimler", "54.34"));
        stocks.add(new StocksBean("vw", "178.48"));
        stocks.add(new StocksBean("allianz", "134.48"));
        stocks.add(new StocksBean("deutschebank", "76.32"));
        stocks.add(new StocksBean("rwe", "80.63"));
        stocks.add(new StocksBean("hypo", "18.79"));
        stocks.add(new StocksBean("deutschepost", "20.19"));
        stocks.add(new StocksBean("telekom", "11.13"));
    }


    /**
     * Send the Stock-Values to the file "index.jsp"
     */
    public void sendStocks() throws InterruptedException {
        WebContext wctx = WebContextFactory.get();
        String currentPage = wctx.getCurrentPage();

        Collection sessions = wctx.getScriptSessionsByPage(currentPage);
        Util utilAll = new Util(sessions);

        for (int i = 0; i < stocks.size(); i++) {
            Thread.sleep(1);
            utilAll.setValue(stocks.get(i).getStock(), stocks.get(i).getValue());
            log.info("Pushing stock: " + stocks.get(i).getStock() + " = " + stocks.get(i).getValue());
        }

    }

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
    <servlet>
        <servlet-name>dwr-invoker</servlet-name>
        <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
        <init-param>
            <param-name>debug</param-name>
            <param-value>true</param-value>
        </init-param>
        <init-param>
            <param-name>pollAndCometEnabled</param-name>
            <param-value>true</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>dwr-invoker</servlet-name>
        <url-pattern>/dwr/*</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app> 

dwr.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"
"http://getahead.ltd.uk/dwr/dwr20.dtd">
<dwr>
    <allow>
        <create creator="new" javascript="StocksDemo">
            <param name="class" value="eu.jdevelop.dwrstocksdemo.StocksDemo"/>
        </create>
    </allow>
</dwr>

I have added the dwr js engine.js and util.js files in webcontent folder.

when i run the project on tomcat and in firefox. On click the getStocks button which triggers the javascript getStock() method. I get a session error popup.

And the message in the tomcat console is

1020033 [http-bio-8080-exec-19] ERROR org.directwebremoting.dwrp.Batch -A request has been denied as a potential CSRF attack.

Can anyone please tell me why. Am I missing something?

below is StocksDemo.js created in the browser

// Provide a default path to dwr.engine
if (dwr == null) var dwr = {};
if (dwr.engine == null) dwr.engine = {};
if (DWREngine == null) var DWREngine = dwr.engine;

if (StocksDemo == null) var StocksDemo = {};
StocksDemo._path = '/ReverseAjax/dwr';
StocksDemo.sendStocks = function(callback) {
  dwr.engine._execute(StocksDemo._path, 'StocksDemo', 'sendStocks', callback);
}
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Add

<init-param>
<param-name>crossDomainSessionSecurity</param-name>
<param-value>false</param-value>
</init-param>

to your web.xml .it will work fine.