Retaining the submitted JSP form data

java, jsp, servlets

Solution

Best what you can do is to submit to your own servlet which in turn fires another request to the external webapplication in the background with little help of `java.net.URLConnection`. Finally just post back to the result page within the same request, so that you can just access request parameters by EL. There's an implicit EL variable `${param}` which gives you access to the request parameters like a `Map` wherein the parameter name is the key.

So with the following form

<form action="myservlet" method="post">
    <input type="text" name="foo">
    <input type="text" name="bar">
    <input type="submit">
</form>

and roughly the following servlet method

protected void doPost(HttpServletRequest request, HttpServletResponse response) {
    String foo = request.getParameter("foo");
    String bar = request.getParameter("bar");

    String url = "http://external.com/someapp";
    String charset = "UTF-8";
    String query = String.format("foo=%s&bar=%s", URLEncoder.encode(foo, charset), URLEncoder.encode(bar, charset));

    URLConnection connection = new URL(url).openConnection();
    connection.setUseCaches(false);
    connection.setDoOutput(true); // Triggers POST.
    connection.setRequestProperty("accept-charset", charset);
    connection.setRequestProperty("content-type", "application/x-www-form-urlencoded;charset=" + charset);

    try (OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream(), charset)) {
        writer.write(query);
    }

    InputStream result = connection.getInputStream();
    // Do something with result here? Check if it returned OK response?

    // Now forward to the JSP.
    request.getRequestDispatcher("result.jsp").forward(request, response);
}

you should be able to access the input in `result.jsp` as follows

<p>Foo: <c:out value="${param.foo}" /></p>
<p>Bar: <c:out value="${param.bar}" /></p>

Simple as that. No need for `jsp:useBean` and/or nasty scriptlets.

Problem

Original source