Как же так?
package com.javarush.task.task31.task3101;
import java.io.File;
import java.io.*;
import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.EnumSet;
import java.util.Map;
import java.util.TreeMap;
import java.util.*;
/*
Проход по дереву файлов
*/
public class Solution {
public static void main(String[] args) throws IOException {
String dirName = args[0];
String fName = args[1];
File file = new File(fName);
File res = new File(file.getParent() + "/allFilesContent.txt");
FileUtils.renameFile(file, res);
FileOutputStream out = new FileOutputStream(res, true);
File folder = new File(dirName);
for (File f: folder.listFiles()) {
if (f.length() <= 50) {
/* FileInputStream input = new FileInputStream(f.getAbsolutePath());
byte[] b = input.readAllBytes();
out.write(b);
out.write("\n"); */
}
}
out.close();
}
}