Java - read file from stream from the end

Question

i wonder if there is a way to read text file line by line from the end from FTP server. I need to read large file, and I'm interested only in the last few lines.

I am able to read last line from file on my HD with code from this question: Quickly read the last line of a text file?, and I am able too to read file on FTP server line by line with code from there: Java. Read file from FTP but DON'T download it whole.

But in first case function tail uses variable type File, while second code uses variable type InputStream.

When I was looking for way of conversion stream to file, I found that only real way is download content to tmp file (How to convert InputStream to virtual File). But I don't want to download this file, because it may be be very large, as I wrote.

Does anybody know another way to do this?

I dont think we can read file starting from last line from FTP server. You have to download file first . — Achintya Jha, Sep 24 '13 at 09:16

score 1 · Accepted Answer · answered Sep 24 '13 at 09:15

1

It's not possible. But you can read the input stream line by line and remember the only few last lines. If the next line comes, just forget the first read line.

answered Sep 24 '13 at 09:15

agad

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Thank You. In case of large file, what will be better and more efficient: Your solution or save file on the disk and read last (few) lines? – Line Sep 24 '13 at 09:58
This solution is faster as you skip one step - saving the file on disk. The rest of the process is the same - just use input stream obtained from ftp server instead of local file: – agad Sep 24 '13 at 10:06
When I save file on disk, I can use code to read it from the end, without read each line from the beginning, with Eric Leschinski code from http://stackoverflow.com/questions/686231/java-quickly-read-the-last-line-of-a-text-file, as I wrote in question. – Line Sep 24 '13 at 10:12
This solution is faster as you skip one step - saving the file on disk. The rest of the process is the same - just use input stream obtained from ftp server instead of local file: `BufferedReader in = new BufferedReader(ftpStream); ... in.readLine();` – agad Sep 24 '13 at 10:14

score 1 · Answer 2 · answered Sep 24 '13 at 09:31

It is not possible using the FTP protocol. The protocol only supports fetching the file starting at the beginning. (There is an optional feature that allows an interrupted transfer to be restarted half way through, but it depends on the server sending opaque "markers" that represent possible resumption points. I cannot see how you could use this to skip to the end of an arbitrary file.)

If you are looking at alternatives, consider using HTTP with a combination of HEAD requests, and GET requests with Range headers. (This depends on the server recognizing those requests ...)

Java - read file from stream from the end

2 Answers2