Contradicting info about resources accessing

Question

Hello,
I am a servlet newbie. I have gone through a lot of posts
in the archives on accessing resources and now I am confused
more than ever. The problem is that my guestbook servlet's doPost() will
read and write a file on the same server.
Now some posts say it should be rare that the servlet is called by two users at the same
time and you shouldn't be worried about file locking. While other posts
imply I need to make the servlet a single Thread servlet for this to work.
And yet another group of posts suggest I could use normal servlet and
synchronize the methods that read and write.
So what exactly is the way to go about read and write one file?
Any hints would be much appreciated!

Answer 1

Now some posts say it should be rare that the servlet
is called by two users at the same
time and you shouldn't be worried about file locking.Very dangerous. If your app allows concurrent users, you must deal with concurrency issues.
While other posts
imply I need to make the servlet a single Thread
servlet for this to work.If every user's session writes to the same file, then a single thread servlet will not solve the problem. You'll just have multiple instances of a servlet writing to one file instead of multiple threads of the same instance writing to one file.
And yet another group of posts suggest I could use
normal servlet and
synchronize the methods that read and write. Sounds like the safest approach. If the same flat file is used by all, then synchronization is necessary. Create a class that handles all i/o to your file and add the synchronization code there.