many applets accessing one writing servlet ...

[Serethos]

i have a game - applet which includs a highscore. to save the scores permanently theres also a servlet for accessing the server resources. so if theres a new highscore reached the applet sends it to ther servlet, which writes the score in a txt-file on the server.
but im smelling problems if several applets are running at the same time:
for each applet instance a unique servlet connection is created for highscore entry. so only crap would happen if one connection writes to the file, another one reads at the same time and so on.

how can i safely synchronize the data ?

btw: for this project i have no access to a database (which would make many problems obsolete ...)