How to get specific line from a txt file in java

Question

I'm dumping info about all the processes running on my pc into a .txt file. To do this I execute handle.exe from my java application. The file contains all the running processes in this format:

RuntimeBroker.exe pid: 4756 
4: Key           HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image 
8: Event  
   10: WaitCompletionPacket 
   1C: IRTimer       
   20: WaitCompletionPacket 
   24: IRTimer       
   28: File          \Device\CNG

--

SearchIndexer.exe pid: 5616 
4: Event         
8: WaitCompletionPacket 
C: IoCompletion  
1C: IRTimer
20: File          \Device\0000007s
22: Directory

I need to get the name of the process that is using a given device i.e. if I'm looping through the file searching for the string "\Device\0000007s", I need to get the name of the process and the process id which is a few lines above. Does anybody know how could I do this? The processes are delimited by a line of dashes -- in the file. Bear in mind that the file is massive, this is just an example.

Does it have to be Java? awk is made for this sort of thing. — cxw
– cxw, Commented Oct 17, 2016 at 19:48
Possible duplicate of How to read a specific line using the specific line number from a file in Java? — nhouser9
– nhouser9, Commented Oct 17, 2016 at 19:48
You could simply replace out all the spaces, break on the delimiter and loop through to grep/regex the string you are looking for. Once you have that just use String methods to pull out "pid:[0-9][0-9]+" im just spitballing here but experiment with that. — Iofacture
– Iofacture, Commented Oct 17, 2016 at 19:51
The thing is I don't know yet the string I'm looking for, the file could be in use by any process with any process name. As if I need to go backwards into the file until the line of dashes and then one line ahead to get the process name, I'm struggling so bad — Tofetopo
– Tofetopo, Commented Oct 17, 2016 at 19:55

Adam · Accepted Answer · 2016-10-17 19:58:36Z

1

I would read each line of a process (using a Scanner) into a List<String>. Then search through the List<String> for your desired String and if it is there, do your processing. Here is some psuedo-code:

Scanner scanner = new Scanner("path/to/file.txt");
List<String> stringList;
while(scanner.hasNextLine()) {
  String nextLine = scanner.nextLine();

  if(nextLine.equals("--") {
    for(String line : stringList) {
      if(line.contains("\Device\0000007s") {
        // Do your processsing here
      }
    }

    stringList.clear();
  }

  else {
    stringList.add(nextLine);
  }

}

This is just psuedo-code, doesn't handle the edge case of the last process and probably won't compile. I will leave the nitty-gritty syntax up to you.

There is probably a more optimal way of doing this, with less looping. But for simple things like this I much prefer a clear approach to an optimized one.

edited Oct 17, 2016 at 19:58

answered Oct 17, 2016 at 19:53

Adam

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1 Comment

Tofetopo Over a year ago

Nice one Adam Rosini, I'll give this a try and see if it doesn't take ages looping and finding the string as I need this to a be quite quick process. Cheers!

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