Java文件不会在所有行的末尾保存新行

Question

I've a problem with saving data to csv file. When I want save data, it saves it sth like this:

new data
2017-02-12
new

But I'd like it save sth like this in the end of the file:

new data,2017-02-12,new

My code:

public static void writeData(String filepath, List<String> lines) {

    Path file = Paths.get(filepath);
    try {
        Files.write(file, lines, StandardOpenOption.APPEND);
    } catch (IOException e) {
        System.out.println("Something went wrong with saving data to file!");
    }
}

Thanks in advance!

Answer 1

Files.write(Path, Iterable<? extends CharSequence>, OpenOption...) is writing to file line by line. If your list contains items "new data", "2017-02-12", "new" then each item will be printed on separate line.

If you want to print them together at single line you have to concatenate them before adding to your list.

String[] columns = new String[] {"new data", "2017-02-12", "new"};
String row = String.join(",", columns);
List<String> rows = new LinkedList<>();
rows.add(row);

// calling your method to save lines
writeData("data.csv", rows);

Answer 2

I guess you are using the wrong function to write the data to your file. To quote the Java API for the function Files::write you are using:

"Each line is a char sequence and is written to the file in sequence with each line terminated by the platform's line separator, as defined by the system property line.separator. " ( source )

The "line separator" is something like "\\n", "\\n\\r", "\\r" (depending on your file system).