Passing parameter to next JSP page by a 3rd-party-Servlet-generated form

I'm trying to fix a bug in a legacy application in my organization. I need to pass an extra parameter in a dynamically generated form.

page1.jsp

<%
    request.setAttribute("param", param);
    // ...
%>

<form name="xx">   
    ...
</form>   
<jsp:include page="servlet1" />

The Servlet1 is calling another Servlet2, which in turn开发者_StackOverflow社区 calls Servlet3 to print some code to page1.jsp. The generated HTML output looks like this:

<form name="xx">   
    ...
</form>   
<form name="yy" action="page2.jsp" >   
    ...   
    <input type="submit">   
</form>  

I need to be able to pass "param" value from page1.jsp to page2.jsp. The request.setAttribute() is not working. The Servlet class Servlet3 is vendor provided, so I cannot set a hidden form variable inside form "yy" to pass it to page2.jsp.

How can I achieve this in other way?

Your easiest bet is to use JavaScript to add a hidden input field to the form. Add the following script to the bottom of your JSP, after the point where the form is been inserted.

<script>
    var input = document.createElement("input");
    input.type = "hidden";
    input.name = "param";
    input.value = "${param}";
    document.forms['yy'].appendChild(input);
</script>

You're however only dependent on whether the enduser supports JS. The only server-side alternative would be to alter the output of Servlet3 yourself with help of HttpServletResponseWrapper.