Java: Find if the last line of a file is empty

问题:

I have a question about a school assignment I need to do it in Java. I need to load data from a file and check for errors in these files.

I read the file with a bufferedReader which works perfectly until the end of the file: it ignores the last line if that line is empty.

I know how to check for empty lines, but the last line simply doesn't give any result using the readLine() function of bufferedReader.

It's important that I know if the last line is empty as it must be. If the empty line doesn't exist, it should give an error.

So long story short, I need a way to tell the difference between the following situations (where CRLF is the end of the line):

Situation 1 (correct):

line x CRLF
line y CRLF

Situation 2 (wrong):

line x CRLF
line y

Both of these situations will return a null on readline() after line y.

I am counting the lines of the file on the way, so if I have a line counter (Note: that counter must count that empty line too, all the ones I found did not count them)

The files contain empty lines throughout too, if that should make any difference for the code I need (these lines are properly detected as they should be as the EOF isn't on these lines)

Note that the program works with or without that last line, it's purely that the assignment tells me to give an error if it's not there.

回答1:

If you want to determine if the last line has a CRLF you can read from the end.

public static boolean lastLineisCRLF(String filename) {
    RandomAccessFile raf = null;
    try {
        raf = new RandomAccessFile(filename, "r");
        long pos = raf.length() - 2;
        if (pos < 0) return false; // too short
        raf.seek(pos);
        return raf.read() == '\r' && raf.read() == '\n';
    } catch (IOException e) {
        return false;
    } finally {
        if (raf != null) try {
            raf.close();
        } catch (IOException ignored) {
        }
    }
}

回答2:

Have a look at java.util.Scanner. You'll be able to iterate using Scanner#hasNextLine() and Scanner#nextLine().

Scanner scanner = new Scanner(file, "UTF-8");
String currentLine = null;
while(scanner.hasNextLine()) {
  currentLine = scanner.nextLine();
}
// last line
System.out.println(currentLine);

回答3:

There is no empty line in your "situation 1". The CRLF belongs to line y and after that, there is nothing (which is what readline() tells you too). It's just that in an editor, this CRLF tells the cursor to go one line down, so it looks like a new, empty line there, but in fact that's just an 'optical illusion' caused by the editor interpreting the characters CR/LF as a hint to show the cursor in a new line.

回答4:

while ((tmp = br.readLine()) != null) {
    strLine = tmp;
}

String lastLine = strLine;

This would give you the last Line of the file. Why not check if the last line is empty or not ?