如何使用Java将文件夹中的所有文件读取到一个单独的文件中？

import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;
public class Test {
   public static void main(String args[]) throws IOException {
      //Creating a File object for directory
      File directoryPath = new File("D:\SampleDirectory");
      //List of all files and directories
      File filesList[] = directoryPath.listFiles();
       System.out.println("List of files and directories in the specified directory:");
      Scanner sc = null;
      StringBuffer sb = new StringBuffer();
      for(File file : filesList) {
         System.out.println("File name: "+file.getName());
         System.out.println("File path: "+file.getAbsolutePath());
         System.out.println("Size :"+file.getTotalSpace());
         //Instantiating the Scanner class
         sc= new Scanner(file);
         String input;
         while (sc.hasNextLine()) {
            input = sc.nextLine();
            sb.append(input+" ");
         }
         System.out.println("Contents of the file: "+sb.toString());
         System.out.println(" ");        
           //Instantiating the FileOutputStream class
         FileOutputStream fileOut = new FileOutputStream("D:\output.txt");
         //Instantiating the DataOutputStream class
         DataOutputStream outputStream = new DataOutputStream(fileOut);
         //Writing UTF data to the output stream
         outputStream.write(sb.toString().getBytes());
         outputStream.flush();
         System.out.println("Data entered into the file");
      }
   }
}

List of files and directories in the specified directory:
File name: sample1.txt
File path: D:\SampleDirectory\sample1.txt
Contents of the file: sample text file1

Data entered into the file
File name: sample2.txt
File path: D:\SampleDirectory\sample2.txt
Contents of the file: sample text file2

Data entered into the file
File name: sample3.txt
File path: D:\SampleDirectory\sample3.txt
Contents of the file: sample text file3

Data entered into the file