Tomcat exception Cannot call sendError() after the response has been committed?

Question

While doing some operations in my application I got

java.lang.IllegalStateException Cannot call sendError()

When I reload the page again it work some time properly, but after some time again it shows the same exception. How can I overcome this exception?

Below is the exception:

HTTP Status 500 - Cannot call sendError() after the response has been committed
type Exception report
message Cannot call sendError() after the response has been committed
description The server encountered an internal error that prevented it from fulfilling this request.
exception 
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:451)
org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:725)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.40 logs.

Struts.xml

<struts>
    <package name="default" extends="hibernate-default">
        <action name="addUser" method="add" class="com.demo.action.UserAction">
            <result name="input">/register.jsp</result>
            <result name="success" type="redirect">list</result>
        </action>
        <action name="list" method="list" class="com.demo.action.UserAction">
            <interceptor-ref name="basicStackHibernate" />
            <result name="success">/list.jsp</result>
        </action>
    </package>
</struts>

Answer 1

This error is a symptom of some other problem, not the root cause you're looking for.

This error explains why the user can't be redirected to the error page. (Reason: the server has already flushed part of the response buffer back to the client - it's too late to switch/redirect to the error page.)

As the error message points out, check elsewhere in your Apache Tomcat 7 logs (or debug your app another way) to find what is throwing an exception.