Oracle Stopping - Can't Login All Of A Sudden - I'm having  a problem with Oracle, it happens randomly around once in three weeks or once a month. The instance that i'm using suddenly hangs, and no logins can be established to it.It won't accept connections and I can't login to it.
I would see no error in the alert logs. I would restart my application but the application still can't connect to it. There were no locks at that time. The thing is, there was no error in the alert logs as well, it would just hang all of a sudden. The only way to recover is to restart it. In my java thread dumps, I would see that the application is hanging at Socket.read part

What are Oracle's problems when I can't login to it at all? I can't initialize a connection that's why I need to resrtart the database. After restarting, I can connect again. There are no error on the alert logs.

What do you think I should look at?

Thanks
Start monitoring memory usage. Does your application terminate old sessions? If not, there is a connection leak that eventually takes away all processes your database instance can use and prevent new connections. There also could be a memory leak, that is why monitoring memory and swap could be smart to do.

Most likely to me seems to be the connection leaking. You can easily monitor this by making counts of v$session or v$process. These counts should not grow unlimited.
Since you use jdbc (thin client I asume) Dead Client Detection could also be useful. This gives the rdbms the ability to clean up unused sessions. Unused sessions are those that do not react upon a ping from the server.