java util

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class FooBarMainEntry {

    public static void main(String[] args) {
        String done = FileHelper.readFileToString("");
        List<String> all = FileHelper.readFileToStringList("");
        List<String> notDone = all.stream()
                                    .map(String::trim)
                                    .filter(line ->{return !done.contains(line);} )
                                    .collect(Collectors.toList());
        FileHelper.overWriteStringListToFile("", notDone);
    }
}


class FileHelper {
    public static String readFileToString(String filePath){
        String content = "";

        try{
            content = new String ( Files.readAllBytes( Paths.get(filePath) ) );
        }
        catch (IOException e){
            e.printStackTrace();
        }

        return content;
    }

    public static List<String> readFileToStringList(String filePath)
    {
        List<String> result=new ArrayList<String>();
        try (Stream<String> stream = Files.lines( Paths.get(filePath), StandardCharsets.UTF_8)){
            stream.forEach(s -> result.add(s));
        }
        catch (IOException e){
            e.printStackTrace();
        }
        return result;
    }

    public static void overWriteStringToFile(String filePath, String content) {

        try{
            BufferedWriter writer = new BufferedWriter(new FileWriter(filePath));
            writer.write(content);
            writer.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }

    public static void appendStringToFile(String filePath, String content) {

        try{
            BufferedWriter writer = new BufferedWriter(new FileWriter(filePath, true));
            writer.append(content);
            writer.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }

    public static void overWriteStringListToFile(String filePath, List<String> content) {
        if(content.isEmpty()) {
            return;
        }
        try{
            BufferedWriter writer = new BufferedWriter(new FileWriter(filePath));
            writer.write(content.get(0));
            writer.append("
");
            for(int i =1; i< content.size()-1;++i) {
                writer.append(content.get(i));
                writer.append("
");
            }
            writer.append(content.get(content.size()-1));
            writer.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }

    public static void appendStringListToFile(String filePath, List<String> content) {
        if(content.isEmpty()) {
            return;
        }
        try{
            BufferedWriter writer = new BufferedWriter(new FileWriter(filePath, true));
            for(int i =0; i< content.size()-1;++i) {
                writer.append(content.get(i));
                writer.append("
");
            }
            writer.append(content.get(content.size()-1));
            writer.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }
}