How to read multiple csv files from a folder in java?

List<String> filenames = new LinkedList<String>();
public void listFilesForFolder(final File folder) {
    for (final File fileEntry : folder.listFiles()) {
        if (fileEntry.isDirectory()) {
            listFilesForFolder(fileEntry);
        } else {
            if(fileEntry.getName().contains(".csv"))
                filenames.add(fileEntry.getName());
        }
    }
}

final File folder = new File("/home/you/Desktop");
listFilesForFolder(folder);

This way, only have to loop over the filenames list, and access how you already know

If you use FileFilter or FileNameFilter, you can get either a list of files for a later iteration or you can do something with every single file inside in the accept method.

String path = "conf/files";

File [] files = new File(path).listFiles(new FileFilter() {
    @Override
    public boolean accept(File path) {
        if(path.isFile()) {
            //Do something with a single file
            //or just return true to put it in the list
            return true;
        }
        return false;
    }
}); 
//Do something with the list of files

With a lambda expression a solution can be achieved in one line:

File [] files = new File("path/to/folder/").listFiles(obj -> obj.isFile() && obj.getName().endsWith(".csv"));

You can easily achieve this using Files class from nio package

 RequiredType type = 
        Files.walk(Paths.get("conf/files"), 2)
                .filter(x -> x.getFileName().toString().endsWith(".csv"))
                .map(x -> {mapping logic})
                .toArray(RequiredType[]::new);

filter() will return Stream of Path, you'll need the map them using map() function after mapping them collect in the array of required type

Another way to read all .csv file in your folder directory by directory.

String inputFolder = "E:\\CSVFiles\\take";//input path where you read the file 
File folder = new File(inputFolder); 
List<String> listOfFiles=listDirectory(folder, 0);  //0 is the level where we start reading

//This method for Reading the file in directory manner(folder under folder all the csv)
private static List<String> listDirectory(File file, int level) {

    List<String> lstFiles = new ArrayList<String>();

    File[] firstLevelFiles = file.listFiles();
    if (firstLevelFiles != null && firstLevelFiles.length > 0) {
     for (File aFile : firstLevelFiles) {
      if (aFile.isDirectory() && !"ProcressedEMLs".equalsIgnoreCase(aFile.getName())
        && !"FailedEMLs".equalsIgnoreCase(aFile.getName())) {
       lstFiles.addAll(listDirectory(aFile, level + 1));
      } else if (!aFile.isDirectory()) {
       if (aFile.toString().toLowerCase().endsWith(".csv")) {
        lstFiles.add(aFile.getAbsolutePath());
       }
      }
     }
    }
    firstLevelFiles = null;
    return lstFiles;
}