RMSCookieConnector - Using Cookies in J2ME

By: Michael Juntao Yuan and Ju Long Emailed: 1728 times Printed: 2337 times    

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The RMSCookieConnector class stores cookies in an RMS record store. An RMS record store is accessed by its name, rather than reference, and can persist between soft resets, or reboots. That ensures an old session remains valid when a user later returns to an application after previously quitting it. Considering most people use their mobile information devices for many different tasks simultaneously, cookie persistence is a desired feature.

Remember, RFC 2109 allows us to separate cookies for different sites by examining the domain attribute associated with each cookie. However, implementing the full specifications in RFC 2109 requires rather complex string parsing and proves quite expensive in terms of memory footprint and CPU usage. Instead of being fully specification-compliant, we decided to use a simpler approach: We simply discard all the attributes information accompanying the set-cookie header and associate each cookie with the real host it comes from. We derive the host name from a call to HttpConnection.getHost(). When we connect to that host again, only cookies from the same host will be used.

We store these cookies and their host names in an RMS record store. An RMS record store only has a one-dimensional structure with sequentially ordered data fields. Starting from field number zero, we store cookies in even-numbered fields and associated host names in the odd numbered fields that directly follow each cookie field. The cookie storage and retrieval code is illustrated below:

// Get cookies from the connection and store them with host names.
static void getCookie(HttpConnection c) throws IOException {
  RecordStore rs = RecordStore.openRecordStore(cookieStoreName, true);

  // "While" loop to iterate through headers and get cookies
  // in to cValue strings.
  /* Start loop. */
    // Write the cookie into the cookie store.
    int newID = rs.addRecord(cValue.getBytes(), 0, cValue.length());
    // We set the domain default to the current server.
    String dValue = c.getHost();
    if ( dValue == null ) {
      // If there is no valid domain,
      // we do not keep the cookie.
        rs.deleteRecord(newID);
    } else {
      // All upper case for easy comparison in the future.
      dValue = dValue.toUpperCase();
      // Write the domain into the cookie store.
      rs.addRecord(dValue.getBytes(), 0, dValue.length());
    }
  /* End loop. */

  rs.closeRecordStore();
  return;
}

// Fetch cookies from record store and set into the connection header.
static void addCookie(HttpConnection c, String url) throws Exception {
  String domain;
  // Chunk of code to parse domain from input url.
  
  StringBuffer buff = new StringBuffer();;
  RecordStore rs = RecordStore.openRecordStore(cookieStoreName, true);
  RecordEnumeration re = rs.enumerateRecords(null, null, false);
  String cookie = "", cookieDomain = "";
  // Iterate through the cookie record store and find cookies
  // with domain matching the current URL.
  //
  // isCookie is used to tell whether the current record is
  // a cookie or an associated domain.
  boolean isCookie = true;
  while ( re.hasNextElement() ) {
    if ( isCookie ) {
      cookie = new String(re.nextRecord());
    } else {
      cookieDomain = new String(re.nextRecord());
      // Cookies are valid for sub-domains.
      if ( domain.endsWith( cookieDomain ) ) {
        buff.append( cookie );
        buff.append("; ");
      }
    }
    isCookie = !isCookie;
  }
  rs.closeRecordStore();

  // If we do have cookies to send, set the composed string into
  // "cookie" header.
  String cookieStr = buff.toString();
  if ( cookieStr == null || cookieStr.equals("") ) {
    // Ignore.
  } else {
    c.setRequestProperty( "cookie", cookieStr );
  }
  return;
}

Following the examples, you can associate each cookie with more properties, such as URL path and expiration time, in real-world applications when such needs arise.


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