try (FileReader fr = new FileReader("in.txt");
        BufferedReader br = new BufferedReader(fr))
{
    String line = br.readLine();
    String[] numbersStrings = line.split(",");
    double[] numbers = new double[numbersStrings.length];
    for (int i = 0; i < numbersStrings.length; i++)
    {
        numbers[i] = Double.parseDouble(numbersStrings[i]);
    }
    System.out.println(Arrays.toString(numbers));
}
catch (IOException e)
{
    e.printStackTrace();
}

double[] numbers = br.lines()
        .flatMap(e -> Stream.of(e.split(",")))
        .mapToDouble(Double::parseDouble)
        .toArray();
System.out.println(Arrays.toString(numbers));