Continuous File reading

Question

I have very different scenario in my application. I need to read some text file and do some some work on that.

Actually what I want is, when I reach to the end of line, my file reading cursor in Java will stop there and wait until the new line append in the text file. Actually the file which I am reading is a real time logs which are generated by the server, the log will generate after every one second.

So I want that my file reading process will never end, it keep on reading file as new data comes in the file.

I have written this code,

 try {
        Scanner sc = new Scanner(file);

        while (sc.hasNextLine()) 
        {
            String i = sc.nextLine();

            processLine(i);    //a method which do some stuff on the line which i read
            if(thread==1)
            {
             System.out.print("After loop in the file"); //just for printing
            }
            while(!(sc.hasNextLine()))     //in the loop until new line comes 
                {
                    System.out.println("End of file");
                    Thread.sleep(100000);
                    System.out.println("Thread is waiting");
                    thread++;
                }
            if(thread==1)
                {   
                    System.out.println("OUt of the thread");
                }
   //System.out.println(i);
        }
        sc.close();
        System.out.println("Last time stemp is "+TimeStem);
        System.out.println("Previous Time Stemp is "+Previous_time);
    } 
    catch (FileNotFoundException e)
    {
        e.printStackTrace();
    }

This is my code, I think my program will remain in the second while loop when end of file reach and when file append it start reading file again. But it's not happening, when end of file is reached, my program wait for some second but never read the next line which is appended in the file.

Also see: http://stackoverflow.com/questions/557844/java-io-implementation-of-unix-linux-tail-f — Aaron Blenkush, Jan 10 '14 at 06:58
1) Use a consistent and logical indent for code blocks. The indentation of the code is intended to help people understand the program flow. 2) A single blank line of white space in source code is *always* enough. Blank lines after `{` or before `}` are also typically redundant. — Andrew Thompson, Jan 10 '14 at 06:58
How can you read from a file which is open and being written into? — TheLostMind, Jan 10 '14 at 07:00
What did you mean by second while loop? I can't see any second while loop. — Helios, Jan 10 '14 at 07:01
@TheLostMind , my logs are real time , which i am reading..And this file going to append after every second because server generate the logs after every second — Malik Ehtasham, Jan 10 '14 at 07:03
@AaronBlenkush thanks for you reply, but i think that is different question. — Malik Ehtasham, Jan 10 '14 at 07:04
@Nik sorry, i have just edit my code, you can see now second while loop — Malik Ehtasham, Jan 10 '14 at 07:06
Yes @AaronBlenkush, i want to wait about 2 minutes. After that my program will start execution again — Malik Ehtasham, Jan 10 '14 at 07:09
Apart from everything else - shouldn't you print your user message before starting to sleep? — norlesh, Jan 10 '14 at 07:14
One more thing I didn't understand is what is use of `thread++` inside second while loop? — Helios, Jan 10 '14 at 07:22
@Nik its just a counter and basically i am checking that will my program comes after the sleep and execute the rest of the line or not. It just for debugging purpose. — Malik Ehtasham, Jan 10 '14 at 07:28

score 2 · Answer 1 · answered Jan 10 '14 at 07:50

public class LogReader {
    private static boolean canBreak = false;

    public static void startReading(String filename) throws InterruptedException, IOException {
        canBreak = false;
        String line;
        try {
            LineNumberReader lnr = new LineNumberReader(new FileReader(filename));
            while (!canBreak)
            {
                line = lnr.readLine();
                if (line == null) {
                    System.out.println("waiting 4 more");
                    Thread.sleep(3000);
                    continue;
                }
                processLine(line);
            }
            lnr.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static void stopReading() {
        canBreak = true;
    }

    private static void processLine(String s) {
        //processing line
    }
}

Continuous File reading

1 Answers1