Hidden Form Fields

You can use hidden form fields like

  <body>
    <form method="get" action="/servlet/hello">
      If you don't mind me asking, what is your name?
      <input type="text" name="name"/>
      <input type="hidden" name="id" value="1234"/>
      <input type="hidden" name="degree" value="bs"/>
      <input type="submit">
      <p/>
    </form>
  </body>

Every html page you generate must be a form and include the hidden fields.

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class ShoppingCartViewerHidden extends HttpServlet {

  public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    res.setContentType("text/html");
    PrintWriter out = res.getWriter();

    out.println("...");
    
    // Cart items are passed in as the item parameter.
    String[] items = req.getParameterValues("item");

    // Ask if the user wants to add more items or check out.
    // Include the current items as hidden fields so they'll be passed on.
    out.println("<form action=\"/servlet/ShoppingCart\" method=\"POST\">");
    if (items != null) {
      for (int i = 0; i < items.length; i++) {
        out.println("<input type=\"HIDDEN\" name=\"item\" value=\"" +
          items[i] + "\">");
      }
    }
    out.println("...");
  }
}