ClassCastexception when casting a Class that extends HttpServletRequestWrap

Question

I have inherited some code that runs OK in JDK 1.4.2 in a JSP, but give s an exception when the JSP runs unfer 1.5.0. My Class is a as follows:
public class WrappedRequest extends HttpServletRequestWrapper {
     public WrappedRequest(HttpServletRequest req) {
          super(req);     
     /** Return value string of requested parameter.
     * <ul>
     * <li> If htmlEncode == NO_HTML_ENCODE, return the native request param, un-html encoded
     * <li> If htmlEncode == HTML_ENCODE, return an html encoded copy of the requested parameter
     * <li> If htmlEncode is neither, return the html encoded copy of the requested parameter     
     * </ul>
     * @param     name               name of the request parameter
     * @param     htmlEncode          whether html encoded/un-encoded parameter value should be returned.
     * @return     String of the requested parameter value. If parameter name is null, return null
     public String getParameter(String name, int htmlEncode) {
          if(name != null && (htmlEncode == NO_HTML_ENCODE)) {
               String str = super.getParameter(name);
               return str;
          else
               return getParameter(name);     
     public String getParameter(String name) {
          String str = super.getParameter(name);
          if(str != null)
               str = Utils.htmlEncode(str); //Another package class
          return str;               
This class in normally invoked as follows:
     String changeApproval = ((WrappedRequest)request).getParameter("CrApp" , WrappedRequest.NO_HTML_ENCODE);
I get a ClassCastException exception on this line. Any suggestions?
Regards,

Answer 1

Stuart_Millington wrote:
Further to my original post I have another question. Please bear in mind that I am fairly new to Java and this is code that I have inherited. In the following line of code (which is the line that causes the exception:
String changeApproval = ((WrappedRequest)request).getParameter("CrApp" , WrappedRequest.NO_HTML_ENCODE);
Why is the request being cast? The following code SEEMS to run OK:
WrappedRequest wr = new WrappedRequest(request);
String CrApproval = wr.getParameter("CrApp" , WrappedRequest.NO_HTML_ENCODE);
Any ideas?
Regards,
Stuart MillingtonOkay, then I understand your problem.
You can only cast request to WrappedRequest when request IS A WrappedRequest - ie the statement request = new WrappedRequest(request) was called. You are apparently trying to convert a default implementation of HttpServletRequest into a WrappedRequest without first 'Wrapping' the request.
What does Wrapping a Request mean and do? A request object is generated by the servlet container and it isn't easy to switch in your own implementation. So instead you make a WrappedRequest which takes the original instance of the HttpServletRequest generated from by the container and adds functionality to it. A WrappedRequest would have to extend an HttpServletRequest, and implement all the public API of said parent class. Most of the time the methods would look something like this:
public String getParameter(String key) { return this.parentRequest.getParameter(key); } That is, it simply delegates most of the work to the HttpServletRequest it is wrapping. But some functions it may want to change behavior for and for those you insert your implementation.
What you need to do:
1) Learn how to use Java before you touch Servlets and server side stuff. You are adding too much complication by going straight to the end game. Use a book and the tutorials to get you through.
2) Take the time to run the JavaEE tutorial.
3) Start with your own code. Taking code snippets you see around the net and trying to get them to work is tough when you don't understand the concepts. For example, using a WrappedRequest is normally fairly useless if it isn't implemented using a Filter, and they work the best when they don't require a change to the request interface (i.e. when you never actually have to do a cast). Since you don't know Filters, and don't yet understand how the wrapper works I would suggest not using them.
This is probably a mis-use of the RequestWrapper idea anyway (since, like I said, it requires a change in interface). What you would be better off doing is simply choosing to pass the parameter through a utility function that does the encoding for you. Example like:
String changeApproval = HTMLEncoder.encode(request.getParameter("CrApp");when you want the parameter encoded and
String changeApproval = request.getParameter("CrApp");when you don't.
If you don't want to make your own utility for this purpose (and why would you) you can download a library that does it for you. One example is the [org.apache.commons.lang.StringEscapeUtils#escapeXML|http://commons.apache.org/lang/apidocs/org/apache/commons/lang/StringEscapeUtils.html#escapeXml(java.lang.String)] class#method from the Apache Foundation. The StringEscapeUtils is part of the Apache Commons Lang project, which you can reach [At the Commons/lang website.|http://commons.apache.org/lang/]