CODEWITHSUNDEEP
javafile
Amr Nassar
Amr Nassar

Reputation: 155

Get the offset of previous line in a file

I'm extracting data from a file line by line into a database and i can't figure out a proper way to flag lines that I've already read into my database.

I have the following code that I use to iterate through the file lines and I attempt to verify
that the line has my flag or else I try to append the flag to the file line

List<String> fileLines = new ArrayList<String>();
File logFile = new File("C:\\MyStuff\\SyslogCatchAllCopy.txt");
try {
  RandomAccessFile raf = new RandomAccessFile(logFile, "rw");
  String line = "";
  String doneReadingFlag = "##";
  Scanner fileScanner = new Scanner(logFile);
  while ((line = raf.readLine()) != null && !line.contains(doneReading)) {
    Scanner s = new Scanner(line);
    String temp = "";
    if (!s.hasNext(doneReadingFlag)) {
      fileLines.add(line);
      raf.write(doneReadingFlag.getBytes(), (int) raf.getFilePointer(),
          doneReadingFlag.getBytes().length);
    } else {
      System.err.println("Allready Red");
    }
  }
} catch (FileNotFoundException e) {
  System.out.println("File not found" + e);
} catch (IOException e) {
  System.out.println("Exception while reading the file ");
}
// return fileLines;
// MoreProccessing(fileLines);

This code appends the flag to the next line and it overwrites the characters in that position Any Help ?

Upvotes: 1

Views: 1640

Answers (2)

Amr Nassar
Amr Nassar

Reputation: 155

@Peter Lawrey I did as you said and it worked for me like that:

as follows:

ArrayList<String> fileLines=new ArrayList<String>();
File logFile=new File("C:\\MyStuff\\MyFile.txt");

RandomAccessFile raf = new RandomAccessFile(logFile, "rw");
String line="";
String doneReadingFlag="#";
long oldOffset=raf.getFilePointer();
long newOffset=oldOffset;

while ((line=raf.readLine())!=null)
{
     newOffset=raf.getFilePointer();    

     if(!line.contains(doneReadingFlag))
     {
           fileLines.add(line);
           raf.seek((long)oldOffset);
           raf.writeChars(doneReadingFlag);
           raf.seek(newOffset);
           System.out.println("Line added and flaged");
     }
     else
     {
           System.err.println("Already Red");
     }
     oldOffset=newOffset;
}

Upvotes: 1

Peter Lawrey
Peter Lawrey

Reputation: 533492

When you write to a file, it doesn't insert do you should expect it to replace the characters.

You need to reserve space in the file for information you want to change or you can add information to another file.

Or instead of marking each file, you can store somewhere the lines number (or better the character position) you have read up to.

If you are not restarting your process you can have process read the file as it is appended (meaning you might not need to store where you are up to anywhere)

Upvotes: 1

Related Questions