How to read a specific position of a string data in a text file

Question

I am processing a text file which contains up to a thousand lines. There are multiple headers and footers in one text file. So I don't need to process the line which contains @h and @f. It tells me the beginning and end of a transaction (Database transaction, I will save those records to DB in one transaction).

A sample record is below. Though the line reaches up to a thousand lines and the columns are up to 40 columns. From each line I am only looking for a specific data i.e (e.g i need to get a name from postion 8 to 30, year from position 60 to 67 and the likes). This position might be next a space or between strings. So I don't want to put the data of each line in to buffer/memory to process it because, I am only interested on few of them. Does CSV file allows to get a data from a specific position in a line? What should I use to get a better performance (to process the data as quick as possible without taking much memory.)? I am using Java

@h Header
@074VH01MATT    TARA   A5119812073921 RONG HI  DE BET IA76200  201108222   0500  *
@074VH01KAYT    DJ     A5119812073921 RONG DED CR BET IA71200  201108222   0500  *
@f Footer

@h Header
@074VH01MATT    TARA   A5119812073921 RONG HI  DE BET IA76200  201108222   0500  *
@074VH01KAYT    DJ     A5119812073921 RONG DED CR BET IA71200  201108222   0500  *
@f Footer

Solution 1

Here is my solution:

import java.io.*;
class ReadAFileLineByLine 
{
 public static void main(String args[])
  {
  try{
    FileInputStream fstream = new FileInputStream("textfile.txt");
    BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
    String strLine;
    //Loop through and check if a header or footer line, if not
    //equate a substring to a temp variable and print it....
    while ((strLine = br.readLine()) != null)   {
      if (!(strLine.charAt(1) == "h" || strLine.charAt(1) == "f"))
        String tempName = strLine.substring(8,31);
      System.out.println(tempName);
    }
    //Close the input stream
    in.close();
  } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

Is something like this what you're looking for?

Solution 2

Use a BufferedReader so it doesn't hold everything in memory constructed from an InputStreamReader so you can specify the character set (as the JavaDoc for FileReader tells to do) - my example below uses UTF-8 assuming the file is in the same encoding.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;

public class StringData {
    public static void main(String[] args) throws Exception {
        BufferedReader br = null;
        try {
            // change this value
            FileInputStream fis = new FileInputStream("/path/to/StringData.txt");
            br = new BufferedReader(new InputStreamReader(fis, "UTF-8"));
            String sCurrentLine;
            while ((sCurrentLine = br.readLine()) != null) {
                processLine(sCurrentLine);
            }
        } finally {
            if (br != null) br.close();
        }
    }

    public static void processLine(String line) {
        // skip header & footer
        if (line.startsWith("@h Header") || line.startsWith("@f Footer")) return;

        String name = line.substring(8, 22);
        String year = line.substring(63, 67);

        System.out.println("Name [" + name + "]\t Year [" + year +"]");
    }
}

Output

Name [MATT    TARA  ]    Year [2011] 
Name [KAYT    DJ    ]    Year [2011]

Solution 3

I don't think CSV is a must, how are you reading the file, line by line or all at once? I would go with line by line, that way, reading each line is not costly in memory (only one line at a time). You can use a regex on the line and take only the groups you need(with Pattern and Matcher) to help extract exactly what you need.