Java File reads and writes

manolakis · 03-31-2009, 12:57 PM

Hi everyone,

I would like to ask something about reading and writing to files. First of all I would like to ask about the canRead/canWrite methods in the File. Will these methods return only the access permissions? Does anybody know any method that can be used to determined if the file is read or written by another program at the same time? I have some programs that deal with the same file (reading and writing) at the same time. What I what to do is to avoid conficts between reads and writes.
Would be grateful for any suggestions.

Thanks.

paulsm4 · 04-01-2009, 11:52 PM

Hi -

What you're asking about is "file locking". Java NIO's "FileLock" might be of interest:

http://java.sun.com/developer/JDCTec...02/tt0924.html

'Hope that helps .. pSM

manolakis · 04-08-2009, 12:52 PM

Hi again,

I am using the following code to read an object from a file:

Quote:

FileInputStream fis = new FileInputStream(USERS_DB_PATH);
ObjectInputStream ois = new ObjectInputStream(fis);
FileLock lock = fis.getChannel().tryLock();

if(lock != null)
{
users = (UsersDatabase) ois.readObject();
lock.release();
}

and I get the following exception

Quote:

Exception in thread "main" java.nio.channels.NonWritableChannelException
at sun.nio.ch.FileChannelImpl.lock(FileChannelImpl.java:773)
at java.nio.channels.FileChannel.lock(FileChannel.java:865)

Any ideas why and how can I avoid it?