konwersja-liter/untitled/src/main/java/FileConverter.java

import java.io.*;
import java.util.Scanner;

public class FileConverter {

    public static String covertFileToUpperCase(String fileFullPath) throws IOException{
        String content = readFile(fileFullPath);
        content = toUpperCase(content);
        return content;
    }

    public static String readFile(String fileFullPath) throws IOException{
        StringBuilder stringBuilder = new StringBuilder();
        File file = new File(fileFullPath);
        Scanner reader = new Scanner(file);
        while (reader.hasNextLine()) {
            stringBuilder.append(reader.nextLine());
            if(reader.hasNextLine())
                stringBuilder.append('\n');
        }
        reader.close();
        return stringBuilder.toString();
    }

    public static String toUpperCase(String content){
        return content.toUpperCase();
    }

}