Creating dynamic URL parameters

Question

I need to access the form value j_username to create a dynamic url but the following JSP code snippet is putting a blank value into �username�. This is before the form is submitted.
Any ideas ?
<input type="button" name="btnPassword" value="Password?" onClick=
"<c:url var="emailMyPwdUrl" value="secure/MailPasswd.do">
                 <c:param name="username"
                 value= "${document.loginForm.j_username.value}"/>
</c:url>
<input type="button" name="btnPassword" value="Password?"
onClick="document.location='${emailMyPwdUrl}';"> ">         I also tried with JavaScript and am having the same problem!
function getLogin() {
    var user = document.loginForm.j_username.value;
    if ( user == '' ) {
            alert( 'No User Name Entered');
      else {
            alert('User Name Entered:' + user);
            <c:url var="emailMyPwdUrl" value="secure/MailPasswd.do">
                    <c:param name="username"
                     value= "${document.loginForm.j_username.value}"/>
            </c:url>
     document.location='${emailMyPwdUrl}';
}

Answer 1

Thanks for your reply,
So basically when the user presses the "btnPassword" button I want to get the value "j_username" from the form and then redirect (no submit!)to "secure/MailPasswd.do" with parameter "username".
I do not want to submit the form when "btnPassword" is pressed as this will cause the "j_security_check" action to take place.
I am correctly redirected to "secure/MailPasswd.do" but the problem is the parameter "username" is blank when I try to getParameter on the "secure/MailPasswd.do" page.
So am I setting the c:param username correctly ?
Here is the full JSP page as I pasted it incorrectly the last time...
c:set var="fullPath" value="${pageContext.request.contextPath}"/>
<form name="loginForm" method="post" action="j_security_check">
<table  border="0"
        width="350"
        height="263"
        align="center"
        background="${fullPath}/images/include/collage.gif"> 
  <tr>
    <td colspan="3" align="center">
      <c:if test="${not empty error}">
        <font class="error">${error}</font>
      </c:if>
    </td>
  </tr>
  <tr>
    <td colspan="3" align="center">
      <c:if test="${not empty message}">
        ${message}
      </c:if>
    </td>
  </tr>
  <tr>
    <td align="center">
      <table border="0"> 
        <tr>
          <td align="right">
            <span class="text">User ID</span>
          </td>
          <td align="left" colspan=2>
            <input type="text" name="j_username" size="21" />
          </td>
        </tr>
        <tr>
          <td align="right">
            <span class="text">Password</span>
          </td>
          <td align="left" colspan=2>
            <input type="password" name="j_password" size="21" />
          </td>
        </tr>
        <tr>
          <td></td>
          <td>
            <input type="submit" value="${buttonLabel}" />
          </td>
          <td>
          <input type="button" name="btnPassword" value="Password?"
            onClick="           
            <c:url var="emailMyPwdUrl" value="secure/MailPasswd.do">
     <c:param name="username" 
                      value= "${document.loginForm.j_username.value}"/>
            </c:url>
          document.location='${emailMyPwdUrl}';"
          </td>
        </tr>
      </table>
    </td>
  </tr>
</table>
</form>