Combining multiple csv files into one using java?

You can use something like this to parse the data: http://opencsv.sourceforge.net/

1) I would parse in each csv into a string array for each line. Compare the initial first lines of each array using a .equals or compareto to make sure you're dealing with the same CSV, you can set this as a check in the first line of the parser, then throw out if they're not of the same type.

Once that's done you can, delete the first lines of all the arrays expect the first array then merge them together, then write a sort method to the data then print to a file.

2) Even easier, take all the CSVs, scan in their first lines, compare them, if they're the same, scan the entire CSV's into multiple string arrays, merge, then using the File class write the array's to the file.csv.

Another CSV parse: http://commons.apache.org/sandbox/csv/apidocs/org/apache/commons/csv/CSVParser.html

Read them in separately, output them into one file. You can also add some code that checks if the records from the two csv files have the same number of columns, otherwise error.

This isn't really a Java-specific problem.

In continuation with user453441's answer, also check for the separator. Many times 'Comma' Separated values are in fact - (because of some business conditions like address line can contain a comma) - separated by different delimiter(s).

    String[] headers = null;
String firstFile = "/path/to/firstFile.dat";
Scanner scanner = new Scanner(new File(firstFile));

if (scanner.hasNextLine())
    headers[] = scanner.nextLine().split(",");

scanner.close();

Iterator<File> iterFiles = listOfFilesToBeMerged.iterator();
BufferedWriter writer = new BufferedWriter(new FileWriter(firstFile, true));

while (iterFiles.hasNext()) {
  File nextFile = iterFiles.next();
  BufferedReader reader = new BufferedReader(new FileReader(nextFile));

  String line = null;
  String[] firstLine = null;
  if ((line = reader.readLine()) != null)
    firstLine = line.split(",");

  if (!Arrays.equals (headers, firstLine))
    throw new FileMergeException("Header mis-match between CSV files: '" +
              firstFile + "' and '" + nextFile.getAbsolutePath());

  while ((line = reader.readLine()) != null) {
    writer.write(line);
    writer.newLine();
  }

  reader.close();
}
writer.close();