Java 7 Watch Service ENTRY_CREATE triggered before file is written

Question

I have a watch service watching a directory. Once files are created, I\'m processing the directory and updating a tree view.

This works fine on ENTRY_DELETE

Answer 1

The event is triggered when a file is created. The file needs to be created before it can be written to. A file doesn't simply appear once it is fully written, it appears once it is created.

What you can do is once you get the creation event:

• Create a File object to point to the file
• Create a java.nio.channels.FileChannel for random access using RandomAccessFile with rw mode (so read & write access)
• Lock the channel. This will block until the file is free for read/write access (read the more general Lock method for more info)
• When the lock is acquired, your file was released by the process that wrote the file

A simplified example:

File lockFile = new File( "file_to_lock" );
FileChannel channel = new RandomAccessFile( lockFile, "rw" ).getChannel( );
channel.lock( );