# locate libjavaplugin_oji.so
# find / -name "libjavaplugin_oji.so" - print
The find command will give you a few errors when hits the /proc directory, but should find it for you. Personally, I like the locate command. You may have to run the updatedb command first to update the database that locate uses to find files.
NOTE: I show these commands as being run by root, but the only one that must be run as root is the updatedb command. With the find command, you'll see a lot more errors (directories that you do not have permission to) it you run it as a non-root user.