WebServer does not update parameter and looses objects

Question

- Please struggle through my loooong explanation - THANKS
Hi all,
I've got a problem with my servlets/JSPs.
I try to build a homepage where the content is displayed dynamically and the start-page is for each link the same.
The content of the pages are stored in HTMLs and XMLs --> the HTMLs contain the static content and also contains identifier for the XMLs which contain the dynamic content. Problem is, that there can be more than one XML. So I've cretaed a properties-file which maps 1-HTML to n-XMLs. So I've generated code which parses (with SAX) through the XMLs and takes the information and stores these information to an object. This object itself is stored with an ID in a hashmap.
Then I go through the HTML (read in a String) and replace the keys (HTML) with the matching value from the Hashmap.
When a page is displayed and the client clicks on a link the same page should be called with parameter http://..../start?lang=de&page=link then I should get the information and the HTML for the "link".
- When I call the "start"-page the first time it is displayed correct. But when I refresh the page it seems as if an object is lost - the information of the Hashmap (which is stored in another object) is lost. I cannot get the information although I got the information before.
Also the parameters are not updated if I change them, there is always the same exception shown, that the key is not available.
I've also changed the parameters (for lang) and just displayed them. But they did not change...
- I'm absolutely helpless
here the servlet:
import java.io.*;
import java.util.HashMap;
import javax.servlet.http.*;
import javax.servlet.*;
public class Start extends HttpServlet {
     private String mPathOfPropertiesFile=IConstants.PROPERTIES_ROOT;
     private String mLanguage;
     private String mIdentifier;
     private String mHtmlAsString;
//class created on my own reads the XML-file and stores all files in a Collection
     private PropertiesXmlReader vXmlPropertiesForIdentifier;
     private HashMap vMapOfFilenames;
     private HashMap vTransUnitId;
     //cretaed on my own. Parses the Collection of XMLfiles and puts necessary information on the FileDisc as Hashmap
private XmlPageParser vParseXmls;
     private FileDesc vFileDesc;
* Implements the HTTP GET method.
* @param request the request object, containing
* data from the browser
* @param repsonse the response object to send
* data to the browser
public void Service (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException{
          mLanguage = request.getParameter("lang");
          if (mLanguage == null){
               mLanguage = "";
          mIdentifier = request.getParameter("page");
          if (mIdentifier == null){
               mIdentifier = "";
               try {
                    // get the relevant Filenames from the Parser
                    vXmlPropertiesForIdentifier = new PropertiesXmlReader(
                              mPathOfPropertiesFile, mLanguage, mIdentifier);
                    // get Filenames
                    vMapOfFilenames = vXmlPropertiesForIdentifier
                              .getFielnames();
                    // parse all XML-Files found in the Properties
                    vParseXmls = new XmlPageParser(vMapOfFilenames);
                    vFileDesc = vParseXmls.getDesv();
                    vTransUnitId = vFileDesc.getMTransUnit();
                    FileReader reader = null;
                    int c;
                    File file = new File(IConstants.HTML_ROOT + mIdentifier);
                    try {
                         // cretae new StringBuffer and read content of the File to the
                         // StringBuffer
                         StringBuffer vHtmlFileBuffer = new StringBuffer();
                         reader = new FileReader(file);
                         while ((c = reader.read()) != -1) {
                              vHtmlFileBuffer.append((char) c);
                         // cretae String to modify
                         String vHtmlAsString = vHtmlFileBuffer.toString();
                         // if not available (-1) = returnvalue
                         boolean vNoMoreReplacements = false;
                         while (!vNoMoreReplacements) {
                              int indexOfStart = vHtmlAsString.indexOf(IConstants.HTML_COMMENT_START);
                              int indexOfEnd = vHtmlAsString.indexOf(IConstants.HTML_COMMENT_END);
                              if (indexOfEnd != -1 && indexOfStart != -1) {
                                   String key = vHtmlAsString.substring(indexOfStart + 3,
                                             indexOfEnd);
                                   TransUnit testUnit = vFileDesc.getTransUnitById(key);
                                   vHtmlAsString = vHtmlAsString.replaceAll(IConstants.HTML_COMMENT_START + key
                                             + IConstants.HTML_COMMENT_END, testUnit.getMSource());
                              } else {
                                   vNoMoreReplacements = true;
                         mHtmlAsString = vHtmlAsString;
                    } catch (FileNotFoundException fileNotFound) {
                         mHtmlAsString = "The HTML-file could not be found, please control root:" + IConstants.HTML_ROOT;
                    } catch (IOException ioErr) {
                         mHtmlAsString = "Exception during output: " + ioErr.getMessage();
                    } finally {
                         if (reader != null) {
                              try {
                                   reader.close();
                              } catch (IOException e) {
                                   e.printStackTrace();
               } catch (Exception e) {
                    mHtmlAsString = "Unexpected exception with text: " + e.getMessage();
          // Returns a writer to write to the browser
     PrintWriter out = response.getWriter();
     // Writes the string to the browser.
     out.print(mHtmlAsString);
     out.close();
Hopefully someone can help me out.
by the way - I'm using a Resin WebbApp Vers 3.0.17
Thanks for help, in advance,
brgds, Steffen

Answer 1

Since you didn't post the XML parser class, I'm not sure exactly what your problem is but I see lots of things that should be changed.
First of all, get rid of the empty Service() method. Fortunately, you named it wrong so it isn't overriding the service() method in the HttpServlet class. If it were overriding the service() method, your servlet wouldn't even work the first time since there would be nothing to invoke doGet().
You shouldn't be using instance variables for processing requests (i.e. mLanguage, mIdentifier) because your servlet needs to be thread-safe. Essentially, there is usually one instance of your servlet around (this is up to the application server) and that one instance must be capable of handling multiple requests simalteously. This isn't causing your problem right now because you are just testing but once the application goes live, this will be a big problem.
Now for what might be causing your problem. Since you didn't post the XML parsers, I suspect that they might be leaving the files open so the second time through, it can't do the parsing. Anyway, your design isn't right because you seem to be reparsing the XML files for each request. All servlets can have an init() method which is invoked when the application server first loads the servlet. You should do all your XML parsing in the init() method. This is much more efficient since it will only be done once (usually when the application server first starts up) not each time the user requests a page. The only potential drawback to this is if you frequently add new XML files, you will have to recycle the server to get the servlet to pick up the new files.