How to submit form using Spring weblow

Below is my code snippet from jsp & flow xml, while trying to submit the form my page is getting refreshed but request is not going to the server. Please assist.

Jsp

<form action="${flowExecutionUrl}" modelAttribute="employeeDto" method="post">
<div class="formButton">
    <input type="hidden" name="_flowExecutionKey" value="${flowExecutionKey}" /> 
    <input  name="_eventId_nextBtn" type="submit" value="submit">
</div>
</form>


Flow xml

<flow xmlns="http://ift.tt/1jwD1YA"  xmlns:xsi="http://ift.tt/ra1lAU"
xsi:schemaLocation="http://ift.tt/1jwD1YA http://ift.tt/1DJTOCc">

<var name="employeeDto" class="com.school.transferobjects.EmployeeDto"/>
<view-state id="employeeView" model="employeeDto" view="employee">
    <transition on="nextBtn" to="createEmployee" />
</view-state>

    <action-state id="createEmployee">
        <evaluate   
        expression="employeeHelper.saveEmployee(flowRequestContext,employeeDto)"
         result="flowScope.res"/>

        <transition on="${flowScope.res.success=='success'}" to="student.do"/> 
    </action-state>

</flow>