Scanner + System.in stop condition

Question

I'm reading a file with Scanner + System.in. My command in Linux looks like:

cat -A test.txt | java -jar test.jar

I'm reading input like:

Scanner input = new Scanner(System.in);

    while (input.hasNextLine())
    {
        String log_line = input.nextLine();
    }

The question is.. How I can stop reading when the end of file is reached?

Not sure how this can be marked a duplicate of a question asked four years AFTER this one was posted. — Michael Armes, Jul 06 '17 at 19:54
@MeghanArmes Time doesn't matter when voting to close as a duplicate. We prefer the better post to be the target. — Patrick Hofman, Jul 06 '17 at 20:03
@Jarrod closing a question as duplicate of closed question is not a good idea, in general. It prevents any way to get new answers. Please reopen. — Shadow The GPT Wizard, Jul 06 '17 at 20:03
@PatrickHofman time does not matter, but question state does, here on Stack Overflow, IMO. Things change in programming, and new answers are required sometimes. So we should not close anything as duplicate of closed question. — Shadow The GPT Wizard, Jul 06 '17 at 20:04
Indeed, but this isn't a new question either, and it didn't receive any attention the last 7 years. @Sha — Patrick Hofman, Jul 06 '17 at 20:05
@PatrickHofman understood -- that makes sense. Thanks for clarifying. — Michael Armes, Jul 06 '17 at 20:05
Please continue the discussion in [this meta post](https://meta.stackexchange.com/q/298092/245360). — Patrick Hofman, Jul 06 '17 at 20:06

score 3 · Answer 1 · answered Nov 30 '10 at 16:06

3

The problem is that System.in never "ends", i.e. EOF is never sent to the stream, so hasNextLine() after the last line is blocking waiting for more data.

The solution is to pass the file name to your app, than you open FileInputStream(filePath) and use it in Scanner constructor.

answered Nov 30 '10 at 16:06

Peter Knego

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strangely, but it works for me (just copy/pasted Serhiy's code and added line echoing to stdout) :) – barti_ddu Nov 30 '10 at 16:12
Myabe there is some alternative to Scanner? I didn't want to pass fileneame through args.. – Serhiy Nov 30 '10 at 16:19
I'm not arguing Your solution (it is better/safer), just curious: http://img13.imageshack.us/img13/3706/scanner.png – barti_ddu Nov 30 '10 at 16:21

score 2 · Accepted Answer · answered Nov 30 '10 at 15:44

2

It seems that problem is -A option, not Your java code (it works correctly on plain files):

$ echo -e "foo\nbar" | java -jar Test.jar 
foo
bar
$

Maybe test.txt contains some non-printable chars that Scanner can't handle...

answered Nov 30 '10 at 15:44

barti_ddu

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test.txt is file generated by another program and all characters looks like fine.. What do you mean with echo? Echo doens't display the content of the file? Previously I was using tail command and the probalem there is with condition to stop..I think so.. – Serhiy Nov 30 '10 at 15:54
I've used echo just for convenience; it doesn't make much difference (and yes, something like `echo -e "1\n2\n3" > test.txt | tail -n 2 test.txt | java -jar dist/Test.jar 2 3 ` works too. By the way, what terminal emulator do You use? – barti_ddu Nov 30 '10 at 16:07
Omg, I must be really stupid or really tired.. Another thread I have wasn't stopping so the program won't exit. THanks a lot for help. – Serhiy Nov 30 '10 at 16:30

Scanner + System.in stop condition

2 Answers2