1 Get End-User Preferences

Logic for processing preferences is distributed throughout the application, which stores the data both in the database and in client-side cookies. The application reads preference data from a cookie whenever possible to improve performance. If it can't get the data from a cookie (for example, because the end-user is visiting the site for the first time, or the end-user's browser does not accept cookies), the application reads preference data from the database.

From a Client-Side Cookie

The two methods below show how the application processes preference data stored in a cookie. Both methods come from xmlnews.common.UserPreference. Here's a sample cookie:

DynamicServlet=3$0$0#4$2$1***242

The cookie uses dollar signs to separate preference values, pound signs to separate categories, and three asterisks as a token to separate user ID and preference data. The sample cookie above shows that user 242 wants items from categories 3 and 4. In category 3, the user wants items of all types in all subcategories (a value of 0 selects all items). In category 4, the user wants items from subcategory 2 only, and within that subcategory, only items of type 1.

The sample app processes such cookies in two steps:

1. First, getNewsCookie gets the "DynamicServlet" cookie from the browser that issued the HTTP request.

2. Then loadPreferenceFromCookie parses it to get a String that contains that user's ID and preferences.

   public Cookie getNewsCookie(HttpServletRequest request)
   

                     throws Exception {
             Cookie c[] = request.getCookies();
             Cookie l_returnCookie = null;
                     for (int i = 0; (c!= null) && (i < c.length); i++) {
                     if (c[i].getName().equals("DynamicServlet")) {
                         l_returnCookie = c[i];
                         }
                       }
                       return l_returnCookie;
                     }
       public Vector loadPreferenceFromCookie(Cookie p_cookie) throws Exception {
             Vector l_prefId = new Vector(2);    
             String l_Preferences = p_cookie.getValue();
             StringTokenizer l_stToken = new StringTokenizer(l_Preferences, "***");
             String l_userId = "";
             while (l_stToken.hasMoreTokens()) {
                // First Token is User Preference.
                l_Preferences = l_stToken.nextToken();
                // Second Token is User ID.
                l_userId = l_stToken.nextToken();
             }
             l_prefId.addElement(l_Preferences);
             l_prefId.addElement(l_userId);
             return l_prefId;
          }
   

Querying the Database

If it can't read preferences from a cookie, the application queries the database. The class xmlnews.common.GenUtility implements methods that connect to the database and fetch news categories, sub-categories, and types.

The semi-dynamic servlet and the dynamic servlet both call these methods and the methods loadInitalPreference and constructUserPreference . These are both implemented in xmlnews/common/UserPreference.java.

Method loadInitalPreference calls getSubCategories, then loops through the result set, combining category values with separator characters to build a preference string.

public String loadInitialPreference(Vector p_category, Vector p_subcategory,
        Vector p_types, Connection p_con)
throws Exception {
GenUtility m_general = new GenUtility();
...
for (int i = 0; i < p_category.size(); i++) {
        String l_cat[] = (String []) p_category.elementAt(i);
        l_category = l_cat[0];
        Vector l_subcategory = m_general.getSubCategories(p_con,l_cat[0]);

        for(int l_j = 0, l_k = 0; l_j < l_subcategory.size(); l_j++, l_k++)
 {
...     
// Append the next preferences to the constructed string
   l_userPref = l_userPref+"#"+l_category+"$"+l_subCat+"$"+l_typeStr;
          }
   }   
...
    return l_userPref;
   }

public static Vector getSubCategories(Connection p_conn, String p_categoryId)
    throws Exception {
    Vector l_subCats = new Vector();

PreparedStatement l_pstmt = p_conn.prepareStatement(
   "Select id, name from sub_categories where category_id = ? ");
    l_pstmt.setString(1, p_categoryId);
    ResultSet l_rset = l_pstmt.executeQuery();

while (l_rset.next()) {
     String[] l_subCat = new String[2];
     l_subCat[0] = new String(l_rset.getString(1));
     l_subCat[1] = new String(l_rset.getString(2));
     l_subCats.addElement(l_subCat);
     }
l_pstmt.close(); 
return l_subCats; 
}

For example, the following code comes from xmlnews.dynamic.DynamicServlet.service.

It calls these methods to read end-user preferences from the database, then uses the preferences to build an HTML page.

public void service(HttpServletRequest p_request, 
      HttpServletResponse p_  response)
      throws ServletException {

   // The following are declared elsewhere as class variables 
   // and initialized in the servlet's init method.
   // GenUtility m_general = null; 

   // m_general = new GenUtility();
   // UserPreference m_userPreference = null;
   // m_userPreference = new UserPreference();
   ...

   // If the database connection has been closed, reopen it.
      if (m_connection == null || m_connection.isClosed())
          m_connection = m_general.dbConnection();
   ...  
      String l_preference = m_userPreference.loadInitialPreference(
      m_general.getCategories(m_connection),
      null, m_general.getTypes(m_connection),
                               m_connection);

m_userPreference = m_userPreference.constructUserPreference
   ( l_preference,m_status);

   // Display the Dynamic Page
      this.sendDynamicPage(l_browserType, p_response, 
      l_userName, m_userPreference,
      m_servletPath + "?REQUEST_TYPE=SET_ADVANCED_USER_PREFS",
      m_servletPath + "?REQUEST_TYPE=LOGIN_REQUEST",
      m_servletPath + "?REQUEST_TYPE=LOG_OUT_REQUEST",
      m_servletPath); 
    ...
 }