flash builder web.xml matter after using RDSDispatchServlet

I encouter a matter when i add

<servlet>
    <servlet-name>RDSDispatchServlet</servlet-name>
    <display-name>RDSDispatchServlet</display-name>
    <servlet-class>flex.rds.server.servlet.FrontEndServlet</servlet-class>
    <init-param>
        <param-name>useAppserverSecurity</param-name>
        <param-value>false</param-value>
    </init-param>        
    <load-on-startup>10</load-on-startup>
</servlet>

in the following web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Micro开发者_JS百科systems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>

    <!-- Http Flex Session attribute and binding listener support -->
    <listener>
        <listener-class>flex.messaging.HttpFlexSession</listener-class>
    </listener>

    <!-- MessageBroker Servlet -->
    <servlet>
        <servlet-name>MessageBrokerServlet</servlet-name>
        <display-name>MessageBrokerServlet</display-name>
        <servlet-class>flex.messaging.MessageBrokerServlet</servlet-class>
        <init-param>
            <param-name>services.configuration.file</param-name>
            <param-value>/WEB-INF/flex/services-config.xml</param-value>
       </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet>
        <servlet-name>RDSDispatchServlet</servlet-name>
        <display-name>RDSDispatchServlet</display-name>
        <servlet-class>flex.rds.server.servlet.FrontEndServlet</servlet-class>
        <init-param>
            <param-name>useAppserverSecurity</param-name>
            <param-value>false</param-value>
        </init-param>        
        <load-on-startup>10</load-on-startup>
    </servlet>

    <servlet-mapping id="RDS_DISPATCH_MAPPING">
        <servlet-name>RDSDispatchServlet</servlet-name>
        <url-pattern>/CFIDE/main/ide.cfm</url-pattern>
    </servlet-mapping>


    <servlet-mapping>
        <servlet-name>MessageBrokerServlet</servlet-name>
        <url-pattern>/messagebroker/*</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
    </welcome-file-list>

    <!-- for WebSphere deployment, please uncomment -->
    <!--
    <resource-ref>
        <description>Flex Messaging WorkManager</description>
        <res-ref-name>wm/MessagingWorkManager</res-ref-name>
        <res-type>com.ibm.websphere.asynchbeans.WorkManager</res-type>
        <res-auth>Container</res-auth>
        <res-sharing-scope>Shareable</res-sharing-scope>
    </resource-ref>
    -->

</web-app>

the matter is that i can't use "data-centric development" feature in flash builder 4.

Try with:

<servlet>
    <servlet-name>RDSDispatchServlet</servlet-name>
    <display-name>RDSDispatchServlet</display-name>
    <servlet-class>flex.rds.server.servlet.FrontEndServlet</servlet-class>
    <init-param>
        <param-name>useAppserverSecurity</param-name>
        <param-value>false</param-value>
    </init-param>    
    <init-param>
        <param-name>messageBrokerId</param-name>
        <param-value>_messageBroker</param-value>
    </init-param>       
    <load-on-startup>10</load-on-startup>
</servlet>

And check that you have added the libs of BlazeDS inside your project.