在tomcat上的webapps / application目录中写日志文件

I write a flex + java application using the blazeds framework. when i write log files in my java classes the default path is the java path on the server. I want it to be my application at the tomcat/webapps/application directory when i write it hard-coded it failed (maybe bacause of permissions) but, i want it to be general (not hard-coded) so, what do i need to change in my java code in order to write files in my webapps directory? maybe it just an xml configuration? what do i need to do? thank you!I write a flex + java application using the bla