I have a directory which contains files like this : {users_20221104.txt | users_20221105.txt | users_20221106.txt

dealers_20221104.txt | dealers_20221105.txt | dealers_20221106.txt |

nations_20221104.txt | nations_20221105.txt | nations_20221106.txt }

I need to retrieve only the last file of each occurence, which means users_20221106, dealers_20221106 and nations_20221106

At the moment I have something like this :

    private void downloadFiles()  {
        List<String> filesPath = ftpClient.listFiles(ftpFolderIn);
        String usersFileTxt = null;
        String dealerFileTxt = null;
        String nationFileTxt = null;
        
        for (String filepath : filesPath) {
            if (filepath.contains("users")) {
                usersFileTxt = filepath;
            }
            if (filepath.contains("dealers")) {
                dealerFileTxt = filepath;
            }
            if (filepath.contains("nations")) {
                nationFileTxt = filepath;
            }
        }
        usersFile = ftpClient.downloadFile(usersFileTxt);
        dealerFile = ftpClient.downloadFile(dealerFileTxt);
        nationFile = ftpClient.downloadFile(nationFileTxt);
    }

CodePudding user response：

Loop through your file names.

Extract the date portion. One way to do this is to use methods on String class such as split and replace.

Parse the date portion as a LocalDate. Use the predefined formatter for parsing the “basic” (condensed) version of the standard ISO 8601 format.

LocalDate ld = LocalDate.parse( input , DateTimeFormatter.BASIC_ISO_DATE ) ;

Compare the dates using their natural ordering, with isBefore, isAfter, and isEqual. Remember which file has the latest date as you loop.

CodePudding user response：

A clean approach would be to create a Compartor corresponding to each prefix and use the same with the stream to find each prefix with the latest (max) date.

Demo:

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Comparator;
import java.util.List;

class DateBasedUserFilesComparator implements Comparator<String> {
  @Override
  public int compare(String s1, String s2) {
    DateTimeFormatter parser = DateTimeFormatter.ofPattern("'users_'uuuuMMdd'.txt'");
    LocalDate ldt1 = LocalDate.parse(s1, parser);
    LocalDate ldt2 = LocalDate.parse(s2, parser);
    return ldt1.compareTo(ldt2);
  }
}

class DateBasedDealerFilesComparator implements Comparator<String> {
  @Override
  public int compare(String s1, String s2) {
    DateTimeFormatter parser = DateTimeFormatter.ofPattern("'dealers_'uuuuMMdd'.txt'");
    LocalDate ldt1 = LocalDate.parse(s1, parser);
    LocalDate ldt2 = LocalDate.parse(s2, parser);
    return ldt1.compareTo(ldt2);
  }
}

class DateBasedNationFilesComparator implements Comparator<String> {
  @Override
  public int compare(String s1, String s2) {
    DateTimeFormatter parser = DateTimeFormatter.ofPattern("'nations_'uuuuMMdd'.txt'");
    LocalDate ldt1 = LocalDate.parse(s1, parser);
    LocalDate ldt2 = LocalDate.parse(s2, parser);
    return ldt1.compareTo(ldt2);
  }
}

public class Main {
  public static void main(String[] args) {
    List<String> files = List.of("users_20221104.txt", "users_20221105.txt", "users_20221106.txt",
        "dealers_20221104.txt", "dealers_20221105.txt", "dealers_20221106.txt", "nations_20221104.txt",
        "nations_20221105.txt", "nations_20221106.txt");

    String usersFileTxt = files.stream().filter(filename -> filename.startsWith("users_"))
        .max(new DateBasedUserFilesComparator()).get();
    System.out.println(usersFileTxt);

    String dealersFileTxt = files.stream().filter(filename -> filename.startsWith("dealers_"))
        .max(new DateBasedDealerFilesComparator()).get();
    System.out.println(dealersFileTxt);

    String nationsFileTxt = files.stream().filter(filename -> filename.startsWith("nations_"))
        .max(new DateBasedNationFilesComparator()).get();
    System.out.println(nationsFileTxt);
  }
}

Learn more about the modern Date-Time API from Trail: Date Time