How should I read inputs from S3 URL?

Question

I have been trying to read data for hackerrank questions, however, although I have tried the following methods, none of them worked properly as explained below. The input file format is like that:

5
2 6 8 9 13

1. Normally I read values with the same format from a local txt file. But when using a local txt file, the code does not work as expected. So, I try to read url with the same method, it does not work as well:

String url= "https://hr-testcases-us-east-1.s3.amazonaws.com/1234/input.txt";
Scanner scan = new Scanner(new File(url)); //I can read from local txt file by using this
Scanner scan = new Scanner(new URL(url).openStream()); //it does not work as well

2. I tried to enter inputs via keyboard, but this also does not work when testing the code in hackerrank.

So, as far as I see, there is a remote txt file and I need to read inputs via Scanner (at least I prefer to use Scanner).

How can I read the values from this remote url?

Answer 1

• You have to use the "actual URI" along with AWSAccessKeyId, and Signature which is what the endpoint requires.
• You are using https://hr-testcases-us-east-1.s3.amazonaws.com/1234/input.txt but that will throw 403 Forbidden.

curl request

curl -v "https://hr-testcases-us-east-1.s3.amazonaws.com/1234/input.txt"
<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>AccessDenied</Code><Message>Access Denied</Message><RequestId>6EC610D00EEF232C</RequestId><HostId>8KIOxrFqKNbjGobVWebrK8hC3QCWm29bQQFsKsvPD4mNooVUbg5E1bXPczUSD3TceWV+Z4jHueM=</HostId></Error>

Working example:

import java.io.IOException;
import java.net.URL;
import java.util.Scanner;

public class ReadUriData {

    public static void main(String[] args) {

        final String accessId="AKIAJ4WZFDFQTZRGO3QA";
        final String signature="JXK3B9GtxpgSEosmgvPBg%2B0UBuI%3D";
        final String url = String.format(
                "https://hr-testcases-us-east-1.s3.amazonaws.com/9828/input00.txt?AWSAccessKeyId=%s&Expires=1593897931&Signature=%s&response-content-type=text/plain",
                accessId, signature
        );

        try {
            String data = readFromUri(url);
            System.out.println(data);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static String readFromUri(String url) throws IOException {
        try (Scanner scanned = new Scanner(new URL(url).openStream())) {

          StringBuilder data = new StringBuilder();
          while(scanned.hasNextLine()){
              data.append(scanned.nextLine()).append("\n");
          }
          return data.toString();
       }
     }
}

output:

6
1 2 3 4 10 11

If you only care about second line of input you can collect them with following code.

private static List<Integer> readFromUri(String url) throws IOException {
        int ROW_FOR_NUMBER_OF_INPUTS = 0;
        try (Scanner scanned = new Scanner(new URL(url).openStream())) {
            List<Integer> data = new ArrayList<>();

            int cursor = 0;
            while (scanned.hasNextInt()) {
                if (cursor == ROW_FOR_NUMBER_OF_INPUTS) {
                    scanned.nextInt();
                } else {
                    data.add(scanned.nextInt());
                }
                cursor++;
            }
            return data;
        }
    }