Problem with a concurrent file access

Question

Hi,
Here is my problems: I have a java program that reads a file in memory, do a few changes and re-write it. It looks like that:
FileInputStream fis = new FileInputStream(tabFilePath);
BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
//Put it in memory and do the stuff...
reader.close();
FileOutputStream fos = new FileOutputStream(tabFilePath, false);
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fos));
// Write it back
writer.close();But, the program is launched a lot of time in the same time, so sometime it crashed with a NullPointerException during the reading part because, (I presume) another process write the file in the same time.
What should I do?
Thanks.

Answer 1

I try this:
FileInputStream fis = new FileInputStream(tabFilePath);
FileLock readLock = fis.getChannel().lock()
BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
//Put it in memory and do the stuff...
readLock.release();
reader.close();
FileOutputStream fos = new FileOutputStream(tabFilePath, false);
FileLock writeLock = fos.getChannel().lock();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fos));
// Write it back
writeLock.release();
writer.close();but I get this exception:
Exception in thread "main" java.nio.channels.NonWritableChannelException
        at sun.nio.ch.FileChannelImpl.lock(FileChannelImpl.java:773)
       ....What's wrong with my code?