apache commons io

  File directoryOrFile = new File(path);

 File[] directoryOrFiles = directoryOrFile.listFiles();

 for(int i=0; i<directoryOrFiles.length; i++) {
   File fileOrDir = directoryOrFiles[i];

   if(file.isFile()) { // fileOrDir이 파일일 경우

   } else if(file.isDirectory()) { // fileOrDir이 디렉터리 일 경우

   }
 }

    // String으로 받고싶은경우 반환형 File을 String으로 바꾸고
    // return문도 주석처리한 코드로 변경하면 됩니다.
    public File getFileByPathToFile(String path) {
        Assert.notNull(path, "path 은 null이 올 수 없습니다.");
        try {
            Resource resource = resourceLoader.getResource(path);
            File file = resource.getFile();
            return file;
      // return file.getCanonicalPath();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

  destinationFileNameExtention = FilenameUtils.getExtension(origin).toLowerCase();

  public class MainClass {
  	public static void main(String[] args) {
  		FileWriter fw, fw_append; // FileWriter 선언

  		try {
  			fw = new FileWriter(".\java_Text.txt", false); // 파일이 있을경우 덮어쓰기
  			fw.write("Writer 1 : Hello world rnWrite Testrn");
  			fw.close();
  		} catch (IOException e1) {
  			e1.printStackTrace();
  		}

  		try {
  			fw_append = new FileWriter(".\java_Text.txt", true); // 파일이 있을경우 이어쓰기
  			fw_append.write("Writer 2 : Append TestrnGoodbye~");
  			fw_append.close();
  		} catch (IOException e1) {
  			e1.printStackTrace();
  		}
  		return;
  	}
  }

public vpid copyOriginalFile(String path) {
  File originalFile = new File(path);
  InputStream is = null;
  OutputStream os = null;

  try {
    is = new FileInputStream(originalFile); // 원본파일
    os = new FileOutputStream(newFolderPath); // 이동시킬 위치

    byte[] buffer = new byte[1024];
    int length;

    while((length = is.read(buffer)) > 0) {
      os.write(buffer, 0, length);
    }
  } catch (IOException e) {
    throw new RuntimeException();
  } finally {
    if(is != null) {
      try {
        os.close();
      } catch (IOException e) {
        throw new RuntimeException();
      }
    }
  }
}

File file = new File("src", "test");
System.out.println("getPath: " + file.getPath());
System.out.println("getAbsolutePath: " + file.getAbsolutePath());
System.out.println("getCanonicalPath: " + file.getCanonicalPath());

File file = new File("../../workspace");
System.out.println("getPath: " + file.getPath());
System.out.println("getAbsolutePath: " + file.getAbsolutePath());
System.out.println("getCanonicalPath: " + file.getCanonicalPath());

public static void main(String[] args) {
    FileInputStream fis = null;
    try{
         fis = new FileInputStream("");
    }catch(IOException e){
      throw new RuntimeException(e);
    }finally {
        fis.close();
    }
}

public static void main(String[] args) {
    FileInputStream fis = null;
    try{
         fis = new FileInputStream("");
    }catch(IOException e){
      throw new RuntimeException(e);
    }finally {
        try {
            fis.close();
        }catch (IOException ie){

        }
    }
}

public static void main(String[] args) {
  FileInputStream fis = null;
  try{
    fis = new FileInputStream("");
  } catch(IOException e){
    throw new RuntimeException(e);
  } finally {
    try {
        if(fis != null) {
            fis.close();
        }
    }catch (IOException ie){
      throw new RuntimeException(e);
    }
  }
}

/**
 * @author Josh Bloch
 * @since 1.7
 */
public interface AutoCloseable {
    void close() throws Exception;
}

public static void main(String[] args) {
    try(FileInputStream fis = new FileInputStream("")){

    }catch(IOException e){
      throw new RuntimeException(e);
    }
}

  // 파일이 존재할 경우 덮어쓰기 : false
  // 파일이 존재할 경우 이어쓰기 : true
  try (FileWriter fileWriter = new FileWriter(getFileFullPath(searchVo), false)) {
        fileWriter.write(searchVo.getContent());
    } catch (IOException e) {
        throw new RuntimeException();
  }

File file = new File("c:/text.txt");
try {
    List lines = FileUtils.readLines(file, "utf-8");
    Iterator it = lines.iterator();
    while(it.hasNext()) {
        System.out.println(it.next());
    }
} catch (IOException e) {
    e.printStackTrace();
}

File file = new File("c:/text.txt");
LineIterator it = null;
try {
    it = FileUtils.lineIterator(file);
    while(it.hasNext()) {
        System.out.println(it.next());
    }
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if(it != null) {
        LineIterator.closeQuietly(it);
    }
}

  String filename = "c:/commons/io/../../lang/../project.txt";
  String normailzed = FilenameUtils.normalize(filename);
  System.out.println(normailzed);

  // 결과 : c:/project.txt

try {
  long freeSpace = FileSystemUtils.freeSpaceKb("c:/");
  System.out.println(freeSpace + "kb");
} catch (IOException e) {
  e.printStackTrace();
}

  try {
    FileUtils.write(new File(getFileFullPath(searchVo)), searchVo.getContent(), "UTF-8");
  } catch (IOException e) {
      throw new RuntimeException();
  }

  private String uploadFile(MultipartFile file) throws Exception {
    /* UUID는 유니크한 ID값을 random으로 toString()화 하고 뒤에 오리지널 파일 명과 합침
    * 장점 : 성능도 괜찮고, 유니크한 ID값을 가질 수있다.
    * 단점 : 파일 명이 길어진다.
    * 서버에 저장된 파일명을 가져와서 uploadPath 경로에 만들고 FileCopyUtils.copy()를 이용해서 쓴다.
    * MultipartFile의 getBytes() 메서드를 이용하여 target에 데이터를 쓴다.
    */
    String save_name = UUID.randomUUID().toString() + "_" + file.getOriginalFilename();
    File target = new File(uploadPath, save_name);
    FileCopyUtils.copy(file.getBytes(), target);
    return save_name;
  }

File file = new File("test.txt");
List<String> ls = FileUtils.readLines(file, "UTF-8");

File file = new File("test.exe");
byte[] contents = FileUtils.readFileToByteArray(file);

File file = new File("test.txt");
String content= FileUtils.readFileToString(file);

  File copy = new File(dir, "testFile1Copy.txt");
  File original = new File(dir, "testFile1.txt");
  // original을 copy로 복사
  FileUtils.copyFile(original, copy);
  FileUtils.forceDelete(testFile2);

public List<String> getFileContents(FileManageHistoryVo historyVo) {
  List<String> fileContents = new ArrayList<>();
  FileReader fileReader = null;
  BufferedReader bufferedReader = null;

  try {
      fileReader = new FileReader(getFileFullPath(historyVo));
      bufferedReader = new BufferedReader(fileReader);
      String line = "";
      while ((line = bufferedReader.readLine()) != null) {            
        fileContents.add(line);
      }
  } catch (FileNotFoundException e) {
      throw new RuntimeException();
  } catch (IOException e1) {
      throw new RuntimeException();
  } finally {
      if (bufferedReader != null) {
          try {
              bufferedReader.close();
          } catch (IOException e) {
              throw new RuntimeException();
          }
      }
      if (fileReader != null) {
          try {
              fileReader.close();
          } catch (IOException e) {
              throw new RuntimeException();
          }
      }
  }
  return fileContents;
}

  public String getFileContents(FileManageHistoryVo historyVo) {
      try {
          return FileUtils.readFileToString(getFileByPathToFile(historyVo.getPath()), Charset.forName("UTF-8"));
      } catch (IOException e) {
          throw new RuntimeException(e);
      }
  }