Redisplay of pages with input errors is one of the things that application frameworks like Struts deal with <http://jakarta.apache.org/struts>. You might want to take a look at that, instead of rolling your own for every single form.
Craig On Fri, 5 Jul 2002, Kevin HaleBoyes wrote: > Date: Fri, 5 Jul 2002 15:21:22 +0100 (BST) > From: Kevin HaleBoyes <[EMAIL PROTECTED]> > Reply-To: Tomcat Users List <[EMAIL PROTECTED]> > To: [EMAIL PROTECTED] > Subject: RequestWrapper question > > It is a common problem that I'm tying to solve. > > I have a web application that has a fill-in form. The user > fills in some of the fields and submits it to a servlet for > processing. The servlet verifies the input request parameters > either directly or using (EJ) Beans. If the input data is not > valid then the form is redisplayed with the previously submitted > values filled in ready for corrections. > > It is this last step that I'm now working on. I'd like to use > JSTL (core) tags in my form and I'll probably have my servlet > directly validate the data (acting as the model and controller). > > Consider the following simple fill-in form: fif.jsp > > <%@ taglib uri="http://java.sun.com/jstl/core"; > prefix="c" %> > > <html><head><title>Test Fill-in Forms</title></head> > <body> > <form method="post" action="TestServlet"> > <input type="text" name="inputstr" > value="<c:out value='${inputstr}'/>"> > <input type="submit" value="Do"> > </form> > </body></html> > > > When the servlet receives the request it looks at the value of > request.getParameter("inputstr") and determines that it is not > correct so it forwards the request back to the fif.jsp page. > > > public class TestServlet extends HttpServlet > { > public void doPost( HttpServletRequest request, > HttpServletResponse response ) > throws ServletException, IOException { > String inputstr = request.getParameter("inputstr"); > // ... but it is not valid > getServletContext().getRequestDispatcher("/fif.jsp"). > forward(request, response); > } > } > > This doesn't work because <c:out> will call > PageContext.findAttribute() which looks for attributes and > not parameters. > Section 3.2 of the JSTL spec says of identifiers: > "searches for the named attribute in page, request, > session (if valid), and application scope(s) in order > and returns the value associated or null" > > I don't think I should set the attribute at the application or > the session levels as they don't seem to belong there. > I dont' know how to set attributes in the > page context so I had a look at the request level. > > I need to add attributes to the request before I forward it but > the setAttribute() method isn't defined for HttpServletRequest. > > So, I have to wrap the request and override the Attribute > related method calls. There seems to be a good example of how > I might do this in the core code of catalina - > org.apache.catalina.core.Application[Http]Request. > > Then I can change TestServlet to use the wrapper and set the > 'inputstr' attribute before forwarding the request. > > public class TestServlet extends HttpServlet > { > public void doPost( HttpServletRequest request, > HttpServletResponse response ) > throws ServletException, IOException { > String inputstr = request.getParameter("inputstr"); > // ... but it is not valid > > // use my own implementation of catalina's core > // Application[Http]Request classes > ApplicationHttpRequest appreq = > new ApplicationHttpRequest(request); > appreq.setAttribute("inputstr", inputstr); > > > getServletContext(). getRequestDispatcher("/fif.jsp"). > forward(appreq, response); > } > } > > > That is what I'm thinking of doing but I wanted to ask a few > questions. > > Does any of the proceeding explanation make sense? > > It doesn't have to be the best way, but > is it one of the possible ways of solving the problem? > > Most of the examples that I've found on RequestWrapper have > been to do with Filters. Any reason why that would be? > > This is a very common problem and many have come before me. > What improvements could I make? What are the other solutions? > > > > Thanks for your help, > Kevin. > > > __________________________________________________ > Do You Yahoo!? > Everything you'll ever need on one web page > from News and Sport to Email and Music Charts > http://uk.my.yahoo.com > > -- > To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> > For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> > > -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
