BufferedWriter does not detect read only directory

Question

I have a java application that reads and writes csv files. I have created a read only directory on my Mac that my application will try to write a csv file to. I did this with chmod 000. No file gets created but no error is thrown either. Furthermore, checking that the file was created with Files.notExists() returns False. My application needs to detect that no csv was created to inform the user. What is going on here?

public void writeCSV(String fileName, List<String> results) throws IOException {
    // fileName = "~/no_write/results.csv"

    try(CSVPrinter printer = new CSVPrinter(Files.newBufferedWriter(Paths.get(fileName)), CSVFormat.DEFAULT.withHeader(header)) {
        for (String result : results) {
            printer.printRecord(result);
        }
    }

    if (Files.notExists(Paths.get(fileName))) { // returns False but no_write directory is empty
        throw new IOException();
    }

    if (!Files.exists(Paths.get(fileName))) { // Files.exists returns True
        throw new IOException();
    }
}

Try use an absolute path, or ask the canonical file path of ~. — Joop Eggen, Oct 08 '21 at 18:49
Files.notExists returns false if the file exists or its existence cannot be determined. So in your case the existence cannot be determined. — Alex Sveshnikov, Oct 08 '21 at 18:54
@JoopEggen You're right! Using the absolute path generates an IOException from the BufferedWriter. — iansumm, Oct 08 '21 at 19:04

score 1 · Answer 1 · answered Oct 08 '21 at 19:13

As mentioned in the comments, the solution is to get the absolute path. When the absolute path is used the directory permissions are picked up and an IOException is generated. No need to check whether the file exists anymore.

public void writeCSV(String fileName, List<String> results) throws IOException {
    // fileName = "~/no_write/results.csv"

    try(CSVPrinter printer = new CSVPrinter(Files.newBufferedWriter(Paths.get(fileName).toAbsolutePath()), CSVFormat.DEFAULT.withHeader(header)) {
        for (String result : results) {
            printer.printRecord(result);
        }
    }
}

BufferedWriter does not detect read only directory

1 Answers1