How to lock a file on different application levels?

Question

Here\'s the scenario: I have a multi threaded java web application which is running inside a servlet container. The application is deployed multiple times inside the servlet

Answer 1

Using java.nio.channels.FileLock, with a ReadWriteLock.

If I were you, I'd hide the File, FileChannel and all FileOutputStream from all business code. Replaced with my own simple adapter class, like an DAO.

e.g.

abstract class MyWriter{
    private FileChannel file;
    public void writeSomething(byte[] b){
        // get VM scope write lock here
        // get file lock here
        // do write
        // release file lock
        // release readwritelock lock
    }
}