How to read nextChar from a file or how to read ip:port from a txt file

Question

sirin_adam 0 Newbie Poster

15 Years Ago

Hello!

I need to read from a txt file ip:port (or in some lines ip:portDdateCinteger). But i can not do it because there is no nextChar method on Scanner class.

The txt file is like this:

332.234.
123.32.45.43.32.11:8976D12.01.2010C5
44.44.
222.333.
111.11.11.11.22.33:8080D01.01.2009C1

...

There are million line on txt file. I need to read one by one from my Java program by reading ip, port, if exist date and check number.

This program must work multi-platform. Thats why i get the end of line string with System.getProperty("line.separator") method.

Can someone help me please?

Thank you!

file-system java

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Latest Post 15 Years Ago Latest Post by sirin_adam

Dani AI

Generated 10 Months Ago

Brief follow-up that ties the thread together and gives a robust, cross-platform solution.

As showed, reading whole lines first is the right idea; as and noted, tokenizers/delimiters can help but they get fragile when some lines have the extra D...C... tail and some do not. A reliable, fast approach is: stream the file line-by-line (so no whole-file memory use), split each line deterministically (not by catching exceptions), and parse the expected pieces. BufferedReader.readLine() (or Files.lines) already handles CR/LF differences across platforms, so no manual line-separator logic is required.

Efficient parsing example (index-based, avoids regex overhead):

try (BufferedReader br = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {
    String line;
    while ((line = br.readLine()) != null) {
        line = line.trim();
        if (line.isEmpty()) continue;
        int d = line.indexOf('D');
        String main = (d >= 0) ? line.substring(0, d) : line;    // ip:port
        String tail = (d >= 0) ? line.substring(d + 1) : null;   // dateCnumber

        int colon = main.lastIndexOf(':');
        if (colon < 0) continue; // malformed
        String ip = main.substring(0, colon);
        int port = Integer.parseInt(main.substring(colon + 1));

        String date = null;
        Integer check = null;
        if (tail != null) {
            int c = tail.indexOf('C');
            if (c >= 0) {
                date = tail.substring(0, c);               // "dd.MM.yyyy"
                check = Integer.parseInt(tail.substring(c + 1));
                // parse date with java.time if needed:
                // LocalDate ld = LocalDate.parse(date, DateTimeFormatter.ofPattern("dd.MM.yyyy"));
            }
        }
        // process ip, port, optional date/check
    }
}

If a single regexp is preferred (precompile the Pattern once for speed), use a pattern such as ([^:]+):(\\d+)(?:D([^C]+)C(\\d+))? and read groups. Tips: precompile Patterns, handle NumberFormatException/date parse errors, trim and skip blank lines, and beware IPv6 (contains ':' — use a different splitting rule for IPv6). For million-line files, avoid per-token Scanner and exception-based control flow — the index-based or precompiled-regex approaches are faster and clearer.

All 9 Replies

harinath_2007 56 Posting Whiz

15 Years Ago

you can use StringTokenizer class inorder to differentiate ip and port

NormR1 580 Posting Sage

15 Years Ago

Have you tried the Scanner class's useDelimiter() method?
Try this:

Scanner input = new Scanner("332.234.32.11.11.222:8080");
            input.useDelimiter("\\.");
            while(input.hasNext()) {
              System.out.println("next="  + input.next());
            }

NormR1 580 Posting Sage

15 Years Ago

i am not sure if the line ends with end_of_line character or 'D' character

If you don't know the delimiters for a line, that makes it very hard to read a "line".
By 'D' do you mean the character 'D' or 0xd ?
What is the format of the data on a line? How will you know when you are at the end of a line?

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sirin_adam 0 Newbie Poster · Answer 1 · 2011-08-18T22:22:53+00:00

StringTokenizer and useDelimiter can not solve my problem :( because i am not sure if the line ends with end_of_line character or 'D' character. StringTokenizer and useDelimiter can split the string if we know which character splits the string. I told you some line has date and check number hut some of them does not.

sirin_adam 0 Newbie Poster · Answer 2 · 2011-08-18T22:46:42+00:00

With that:
read.useDelimiter(" : | " + end_of_line+ "|D|C");
i can not understand if the line ends or not :(

If you don't know the delimiters for a line, that makes it very hard to read a "line".
By 'D' do you mean the character 'D' or 0xd ?
What is the format of the data on a line? How will you know when you are at the end of a line?

I mean the character 'D' .

The format of line is very simple

ip:port OR ip:portDdateCnumber
example for each
332.234. OR 123.32.45.43.32.11:8976D12.01.2010C5

It will be very simple if java scanner had a nextChar() method :( .

End of line character is System.getProperty("line.separator")

NormR1 580 Posting Sage Team Colleague · Answer 3 · 2011-08-18T22:52:22+00:00

End of line character is System.getProperty("line.separator")

On my system that character has a value of 0x0d0a.
What is the value on your system?

String lineSep =  System.getProperty("line.separator");
      System.out.print("l.s="); 
      for(int i=0; i < lineSep.length(); i++)
          System.out.print(Integer.toHexString(lineSep.charAt(i)) + " ");  // l.s=d a

What does the Scanner class do when reading a file with lines separated by 0x0d0a characters? Have you tried that?

sirin_adam 0 Newbie Poster · Answer 4 · 2011-08-18T23:05:00+00:00

On my system that character has a value of 0x0d0a.
What is the value on your system?
String lineSep =  System.getProperty("line.separator");
      System.out.print("l.s="); 
      for(int i=0; i < lineSep.length(); i++)
          System.out.print(Integer.toHexString(lineSep.charAt(i)) + " ");  // l.s=d a
What does the Scanner class do when reading a file with lines separated by 0x0d0a characters? Have you tried that?

My line sperator is "d a" at the moment(i am on windows now). (My program must work multiplatform (linux-unix-win) ).

Why you asked my end seperator ?

NormR1 580 Posting Sage Team Colleague · Answer 5 · 2011-08-18T23:10:00+00:00

Why you asked my end seperator ?

Your program needs to read each line. To do that it needs to know what defines the end of a line.
When a line has been read, then you need to parse the line to get the values from the line.
Are you able to read the file, line by line?
Write a small simple test program to read the first 10 lines from the file and print them out to be sure you can read a line.

sirin_adam 0 Newbie Poster · Answer 6 · 2011-08-19T03:06:09+00:00

I solve the problme. I don't need to understand if i am on end of line. Because i read first all the line and i put it on a string. After that i read the Scanner.next with useDelimiter(" : |D|C"). If it gives error (which i catch it with try-catch) when i read with Scanner.next that means this line includes just ip and port. if it will not give me an error that means it has also date and check numnber. I try it it works :)

Thanks for your helping me... :)

How to read nextChar from a file or how to read ip:port from a txt file

Dani AI

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