Apple WebObjects 3.5 - Manual (Page 130)

Chapter 7 Managing State
130
// Unarchive session
restoredSession = [NSUnarchiver
unarchiveObjectWithData:archivedSession];
return restoredSession;
}
- saveSession:aSession {
id request = [[WOApp context] request];
// Store data corresponding to session only if necessary.
if (![aSession isTerminating] && ![request isFromClientComponent]) {
id sessionData = [NSArchiver
archivedDataWithRootObject:aSession];
id sessionFilePath = [self archiveFileForSessionID:[aSession
sessionID]];
[sessionData writeToFile:sessionFilePath atomically:YES];
}
}
@end
As you can see, when the FileSessionStore receives a saveSession: message, it
checks whether the session object needs to be archived, and if so, it asks
NSArchiver to create a binary archive of the session object and all of the
components it contains. It then invokes its own
archiveFileForSessionID: to determine
the path for the archive file. Finally, it writes the data to the file. Notice that the
session data is written to a file whose name is the session ID itself.
In this implementation, restoreSession restores the state for a particular session. An
interesting point in the restoreSession method implementation is the
setDistributionEnabled: message to the WOContext object (Context in Java). This
method enables application load balancing. As you learned in the earlier section
“State in the Server” (page 123), when state is stored in the server, all requests
from a particular session must access the same application instance on the same
machine. In this example, because session state is stored in the file system and
not in the application’s memory, any application instance can handle any
request. The
setDistributionEnabled: method enables application load balancing by
allowing any application instance to respond to any request.
Note that the Foundation classes NSArchiver and NSUnarchiver aren’t
provided in the Java next.util package and that the WebSession and Component
classes don’t implement the Serializable or the Externalizable interface. For
these reasons, you can’t implement storing state in the file system in Java. If you
want to store Java objects in the file system, you can do so if they implement the
Coding interface, but you must write your equivalent of the FileSessionStore
class in WebScript or Objective-C.