How to write and read from file simultaneously using java?

Question

In my program I am executing a shell script that writes output in a file. I want to display that file contents line by line. These two operations must work simultaneously.

Here is my code:

public static void myfun(String abc) throws IOException, InterruptedException {
    String customer = "xyz";
    nmapoutfile=runMT.instdir+"/var/nmapout."+customer;
    String nmapstatusfile = runMT.instdir+"/logs/nmapout."+customer+".log";
    String nmapdonefile = runMT.instdir+"/logs/nmapout."+customer+".done";

    String nmapcommand=runMT.instdir+"/bin/doscan.sh "+nmapoutfile+" "+IPRange+" "+nmapstatusfile+" "+nmapdonefile;

    System.out.println(nmapcommand);
    Runtime r = Runtime.getRuntime();
    Process pr = r.exec(nmapcommand);
    try {
        BufferedReader inbr = new BufferedReader (new FileReader(new File(nmapstatusfile)));        
    } 
    catch(Exception e){
         e.printStackTrace();
    }
    while (inbr.readLine()!=null){
        System.out.println("Line is .. " + inbr.readLine());
    }
    pr.waitFor();   
}

How do I handle concurrent read and write operation??

Why on earth would you want to do that? This is almost like programming your application to be forced swapping. — Martijn Courteaux, Dec 26 '13 at 12:39
you may refer http://stackoverflow.com/questions/12818341/bufferedreader-readline-when-reading-in-a-thread — codingenious, Dec 26 '13 at 12:39
@Martijn Courteaux - I am writing output of different networking commands. I want to display result of those commands and want to perform action accordingly — Vishwas, Dec 26 '13 at 12:43
You are reimplementing the standard command `tee`. Why don't you look into *using* that command instead and save yourself some headaches. — Marko Topolnik, Dec 26 '13 at 12:45

score 0 · Answer 1 · answered Dec 26 '13 at 12:42

I would suggest you have a look at random access files (see http://docs.oracle.com/javase/tutorial/essential/io/rafs.html). This API is a little more complicated to work with since you'll be reading bytes, not lines, but it should give you what you need.

If you don't want to deal with NIO you can use http://docs.oracle.com/javase/7/docs/api/java/io/RandomAccessFile.html instead.

How to write and read from file simultaneously using java?

1 Answers1