File Locking in Java: Preventing Multiple Processes from Interfering

A common requirement in multi-process scenarios is to prevent one process from modifying a file while another process is accessing it. This is especially crucial in cases where file integrity must be maintained.

Implementing File Locking in Java

To achieve file locking in Java, you can utilize the FileChannel.lock() method. This method provides exclusive or shared locks, depending on your needs.

Example Usage in Your Scenario:

In your specific scenario, you can use FileChannel.lock() in both the "ReadApp" and "WriteApp" as follows:

try (
    FileInputStream readInputStream = new FileInputStream(file);
    FileLock readLock = readInputStream.getChannel().lock();
    Reader reader = new InputStreamReader(readInputStream, charset)
) {
    // ReadApp code
}

try (
    FileOutputStream writeOutputStream = new FileOutputStream(file);
    FileLock writeLock = writeOutputStream.getChannel().lock();
    // Perform writing operations on writeOutputStream
) {
    // WriteApp code
}

Ensuring Safety:

Note that the FileChannel.lock() method throws an OverlappingFileLockException if the file is already locked by another process. This exception can be used as a cue for the "WriteApp" to move to the next file in the directory.

Platform Dependencies:

It's crucial to consider the platform dependencies mentioned in the API documentation for FileLock. Different operating systems may implement file locking differently, affecting the behavior of your code.