private boolean checkFileWritable(final Path path) throws IOException {
        if (path != null) {
            // Open file with append mode and do nothing.
            // If file is not writable, it throws an exception.
            // NOTE: |Files.isWritable| does not work for the purpose as it expects the file exists.
            // Using |Files.newOutputStream| for the binary mode.
            try (final OutputStream output = Files.newOutputStream(path, StandardOpenOption.APPEND, StandardOpenOption.CREATE)) {
                ;
            }
        }
        return true;
    }
Runs the run subcommand.

It receives a ConfigSource and a String as parameters to be called from Ruby (embulk/runner.rb).
embulk-core/src/main/java/org/embulk/EmbulkRunner.java