Hi, Can anyone tell me how to use Servlet filters? Giveme some tutorials to implement servelt filters.
Thanks in advance Murthy -----Original Message----- From: Kevin HaleBoyes [mailto:[EMAIL PROTECTED]] Sent: Friday, July 05, 2002 6:15 PM 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. ___________________________________________________________________________ To unsubscribe, send email to [EMAIL PROTECTED] and include in the body of the message "signoff SERVLET-INTEREST". Archives: http://archives.java.sun.com/archives/servlet-interest.html Resources: http://java.sun.com/products/servlet/external-resources.html LISTSERV Help: http://www.lsoft.com/manuals/user/user.html ___________________________________________________________________________ To unsubscribe, send email to [EMAIL PROTECTED] and include in the body of the message "signoff SERVLET-INTEREST". Archives: http://archives.java.sun.com/archives/servlet-interest.html Resources: http://java.sun.com/products/servlet/external-resources.html LISTSERV Help: http://www.lsoft.com/manuals/user/user.html
