java - How can I lock a file if it exists, don't create it? -

i want test see if can lock file x. if file doesn't exist or can't locked, fail. sounds simple, keep running dead-ends. short-cut answer provide way filechannel can make exclusive lock on, without risk of creating file. let me explain...

i can't use nio lock() without writable filechannel , can't writable filechannel without opening file x in such way if doesn't exist, created. every java method i've found trying open file x writable creates if doesn't exist , there doesn't seem way exclusively lock file on read-only filechannel.

even checking confirm file exists first problematic. here's latest code:

private lockstatus openandlockfile(file file) {              if (files.notexists(file.topath())) {                 synchronized (filelist) {                     removefile(file);                 }                 return lockstatus.file_not_found;             }             try {                    rwfile = new randomaccessfile(file, "rw");                 filelock = rwfile.getchannel().lock();                               }              catch ... 

the problem code file might exist when notexists code runs, gone time new randomaccessfile(file, "rw") runs. because i'm running code in multiple threads , multiple processes means code has air-tight , rock solid.

here's example of problem existing code running in 2 processes:

1: process detects new file

2: process b detects same file

3: process processes file , moves folder

problem ---> process b accidentally creates empty file. oops!!!

4: process b detects new file created process b , processes creating duplicate file 0 bytes.

5: process detects new file accidentally created process b , tries process it...

bigger screenshot

here's example using c# of i'm trying do:

stream istream = file.open("c:\\software\\code.txt", filemode.open,     fileaccess.read, fileshare.none) 

any or hints appreciated! thanks!

if trying prevent 2 threads in same application (same jvm) processing same file, should implementing using regular java locks, not file locks. file locks granted jvm , reentrant ... if 1 thread "locks" file, thread can acquire lock on same file.

what create thread-safe locking class wraps hashset<file>, file objects denote absolute file paths files exist. implement "file locking" locking on file objects.

---

unfortunately not in different jvms, on different server.

in case, best strategy use database implement locks.