Example 7.5 Is Not Thread-Safe

john jimenez added a comment - 10/Feb/10 12:01 AM I made it a major because the back drop of the example is highlighting the inherent thread-safetiness of MDC.

john jimenez added a comment - 10/Feb/10 12:18 AM Instead of synchronizing the points of userRegistered access, one can store it in the session or in this particular implementation the request.

Ralph Goers added a comment - 10/Feb/10 1:12 AM I concur that the way userRegistered is used is not thread safe. However, in this example there is no need to store it in the session or the request. Instead, define registerUserName as private boolean registerUsername(String username) {         if (username != null && username.trim().length() > 0) {       MDC.put(userKey, username);       return truel     }     return false;   } then in doFilter do String userName; if (principal != null) {   username = principal.getName(); } else {   username = (String) req.getSession().getAttribute(userKey); } boolean userRegistered = registerUserName(userName);

Ceki Gulcu added a comment - 18/Mar/10 7:12 PM - edited John, thank you for reporting this issue. It was fixed along the lines suggested by Ralph. (Thanks Ralph).