Validator complaints unclear, especially "Server security exception. You are performing a forbidden or potentially dangerous operation."

Thanks for suggestions. > parsing a String to a number with leading or trailing spaces Changed by adding trim(), but no change in validation result, e.g.: long id = Long.parseLong(line.substring(0, 0 + 8).trim()) > using Locale.US This is done to force String.format to use "." instead of "," for floating point representation. Default locale is German on my local machine. Assuming the server has default locale "US" on server side I tested without explicit definition of Locale.US. No change in validation result. Still "Server security exception" Locale only get's in contact with SecurityManager if one tries to set a new default locale - what I won't do in this code. Stream-Api usage should never cause security manger issues. I've used my code from this task1827 also in task1828 with necessary enhancements for update/delete operations. In task1828 everything validates just fine. So seems the validators in task1827 are simply broken.

public class Solution {
   static class Product { }
   static class ProductList { }

   main() { }
}

One problem that I see is that parsing a String to a number with leading or trailing spaces will result in an exception. This is most likely happening on lines 29 and 34 of your main class. Try fixing that and see what happens. Another thing is I don't think you should be using Locale.US, this may be causing your security warning. In my opinion your code could be greatly simplified by not breaking apart the file into your Product and ProductList classes. You need nothing from the data in the file other than the ID numbers. Also the task is dealing with Strings so other than having to get the max ID there is no reason to convert to numbers. Here is how I would approach it: step 1) read the whole file into a String, so the String would be: "19847 Swim trunks, blue 159.00 12 198479 Swim trunks, black with printe173.00 17 19847983Snowboard jacket with reflecti10173.991234 19847984product1 100.00 100 " step 2, 3, and 4) read the first 8 digits of each line, parse to each to int, figure out the max 5) start a string for the new product with the new ID needed from figuring out the max in that last step 6) continue building that string from the rest of the args 7) write the (whole) file data back to the file. 8) add a line break and write the new product to the file. Adding more steps than is necessary just increases the chance of accidently programming in bugs.

private static int getLastProductId(List<String> products) {
    return Integer.parseInt(products.get(products.size() - 1).substring(0, 8).trim());
}

private static List<String> readProducts(String fileName) throws IOException {
    try (Stream<String> in = new BufferedReader(new FileReader(fileName)).lines()) {
        return in.collect(Collectors.toList());
    }
}