Merge CSV files into a single file with no repeated headers

Question

I have some CSV files with the same column headers. For example

File A

header1,header2,header3
one,two,three
four,five,six

File B

Answer 1

Before:

idFile#x_y.csv

After:

idFile.csv

For example:

100#1_2.csv + 100#2_2.csv > 100.csv

100#1_2.csv contains:

"one","two","three"
"a","b","c"
"d","e","f"

100#2_2.csv contains:

"one","two","three"
"g","h","i"
"j","k","l"

100.csv contains:

"one","two","three"
"a","b","c"
"d","e","f"    
"g","h","i"
"j","k","l"

Source:

//MergeDemo.java
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
//import java.util.Arrays;
import java.util.Iterator;
import java.util.Scanner;

public class MergeDemo {

    public static void main(String[] args) {

        String idFile = "100";
        int numFiles = 3;

        try {
            mergeCsvFiles(idFile, numFiles);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    private static void mergeCsvFiles(String idFile, int numFiles) throws IOException {

        // Variables
        ArrayList files = new ArrayList();
        Iterator iterFiles;
        File fileOutput;
        BufferedWriter fileWriter;
        BufferedReader fileReader;
        String csvFile;
        String csvFinal = "C:\\out\\" + idFile + ".csv";
        String[] headers = null;
        String header = null;

        // Files: Input
        for (int i = 1; i <= numFiles; i++) {
            csvFile = "C:\\in\\" + idFile + "#" + i + "_" + numFiles + ".csv";
            files.add(new File(csvFile));
        }

        // Files: Output
        fileOutput = new File(csvFinal);
        if (fileOutput.exists()) {
            fileOutput.delete();
        }
        try {
            fileOutput.createNewFile();
            // log
            // System.out.println("Output: " + fileOutput);
        } catch (IOException e) {
            // log
        }

        iterFiles = files.iterator();
        fileWriter = new BufferedWriter(new FileWriter(csvFinal, true));

        // Headers
        Scanner scanner = new Scanner(files.get(0));
        if (scanner.hasNextLine())
            header = scanner.nextLine();
        // if (scanner.hasNextLine()) headers = scanner.nextLine().split(";");
        scanner.close();

        /*
         * System.out.println(header); for(String s: headers){
         * fileWriter.write(s); System.out.println(s); }
         */

        fileWriter.write(header);
        fileWriter.newLine();

        while (iterFiles.hasNext()) {

            String line;// = null;
            String[] firstLine;// = null;

            File nextFile = iterFiles.next();
            fileReader = new BufferedReader(new FileReader(nextFile));

            if ((line = fileReader.readLine()) != null)
                firstLine = line.split(";");

            while ((line = fileReader.readLine()) != null) {
                fileWriter.write(line);
                fileWriter.newLine();
            }
            fileReader.close();
        }

        fileWriter.close();

    }

}