如何使用 JAVA 从 txt 文件中删除最后一行？

Question

I have a txt file as follows:

123
156
356
<--- line break  (How delete this?)

I need it like this:

123
156
356 <- let that be my last record.

Answer 1

You can delete the last line using the method described in the post here . But as you may know the EOL (line break) is 2 character long \r\n in windows systems CRLF and 1 character long in macOS/linux systesm \n LF , so you need to delete the last 2 characters if your file is windows formated:

try {
  FileChannel open = FileChannel.open(Paths.get("file.tx"), StandardOpenOption.WRITE);
  open.truncate(open.size() - 2);   //the 2 characters I was describing above
} catch (IOException e) {
  System.out.println("An IO error occurred.");
  e.printStackTrace();
}

Keep in mind that every time you run this code, the last 2 characters will be deleted, so it might be wise for you to implement a check that the EOL are the last characters of your file. You can do that by reading the last characters:

FileChannel read = FileChannel.open(Paths.get("file.txt"), StandardOpenOption.READ);
ByteBuffer buffer = ByteBuffer.allocate(4);
read.read(buffer, read.size() - 2);
if(new String(buffer.array()).contains("\r\n")) {
  FileChannel write = FileChannel.open(Paths.get("file.txt"), StandardOpenOption.WRITE);
  write.truncate(write.size()-2);
}