Question

What is the best way to share a file between two “writer” services in the same application?

Edit:
Sorry I should have given more details I guess.

I have a Service that saves entries into a buffer. When the buffer gets full it writes all the entries to the file (and so on). Another Service running will come at some point and read the file (essentially copy/compress it) and then empty it.

Answer 1

Here is a general idea of what you can do:

public class FileManager
{
    private final FileWriter writer = new FileWriter("SomeFile.txt");
    private final object sync = new object();

    public void writeBuffer(string buffer)
    {
        synchronized(sync)
        {
            writer.write(buffer.getBytes());
        }
    }        

    public void copyAndCompress()
    {
        synchronized(sync)
        {
            // copy and/or compress
        }
    }

}

You will have to do some extra work to get it all to work safe, but this is just a basic example to give you an idea of how it looks.