如何删除Java中文本文件的最后一行？

Question

I have a file that includes a few strings. For example:

Mike1111
Chris2222
Brian3333

I am trying to write code to delete a line from that file. However, when I delete Chris for example, it becomes:

Mike1111
Brian3333
(blank line)

The blank line is a problem because when I add another string it will come after the blank line rather than in it's place. Thank you in advance. Here is my code:

public void deleteUser(String u, String p) throws IOException {
    username = u;
    pin = p;

    File userAccountFolder = new File("userLogin.txt");
    File temporaryFile = new File("temporaryFile.txt");

    BufferedReader buffReader = new BufferedReader(new FileReader(userAccountFolder));
    BufferedWriter buffWriter = new BufferedWriter(new FileWriter(temporaryFile));

    String lineToRemoveFromFile = username + pin;
    String lineFromUserFile;

    while ((lineFromUserFile = buffReader.readLine()) != null) {

        String trimmedLine = lineFromUserFile.trim();
        if (trimmedLine.equals(lineToRemoveFromFile)) {
          continue;
        }

        buffWriter.append(lineFromUserFile + System.getProperty("line.separator"));
    }
    buffWriter.close();
    buffReader.close();

    boolean removed = temporaryFile.renameTo(userAccountFolder);
    if (removed == true) {
        System.out.println(username + "'s account has been removed.");

    }

}

Answer 1

This will do the trick, add one boolean check.

        BufferedReader buffReader = new BufferedReader(new FileReader(userAccountFolder));
        BufferedWriter buffWriter = new BufferedWriter(new FileWriter(temporaryFile));

        String lineToRemoveFromFile = username + pin;
        String lineFromUserFile;

        boolean addnewLine = false;

        while ((lineFromUserFile = buffReader.readLine()) != null) {

            String trimmedLine = lineFromUserFile.trim();
            if (trimmedLine.equals(lineToRemoveFromFile)) {
                continue;
            }

            if (addnewLine) {
                buffWriter.newLine();
            } else {
                addnewLine = true;
            }
            buffWriter.append(lineFromUserFile);

        }
        buffWriter.close();
        buffReader.close();

Answer 2

The problem here is that, with System.getProperty("line.separator") , you append a line at the end of temporaryFile even though no more lines comes in. Code below tries to avoid creating redundant end line:

    String lineFromUserFile = null;
    boolean needAddNewLine = false;
    while ((lineFromUserFile = buffReader.readLine()) != null) {
        if (!lineFromUserFile.trim().equals(lineToRemoveFromFile)) {
            if (needAddNewLine) {
                buffWriter.newLine();
            }
            needAddNewLine = true;
            buffWriter.write(lineFromUserFile);
        }
    }