Easy approach to work with files in Java - Java NIO(New input output)

 

  • NIO - New IO package. Introduced in 1.4. It is buffer based and non-blocking. Hence, faster than IO package. It supports symbolic links, posix file attributes(works only on OS's which are POSIX compliant), ACL (Access control list).
  • Paths and Files are the main classes

Creating a potential file reference:

Path path = Paths.get("c:/demo/"); //possible file reference

Creating a directory, file, write to the file, read from the file:

//create all the non existing directories in the path. Ignores creating a directory, if that directory already exists
Path directories = Files.createDirectories("c:/demo/example1/properties/");

Path newFilePath = Files.createFile("c:/demo/README.txt"); //Creating a file


//Writting bytes to the file
Files.write(newFilePath, "This is a dummy text".getBytes(StandardCharsets.UTF_8));

//Reading bytes from file
String readFile = new String(Files.readAllBytes(newFilePath), "UTF-8");
  • Files.readAllBytes reads all the file contents in one go. 
  • If the file size is large, say in MBs/GBs and you have a memory constraint application. It is advisable to use BufferedReader and read the file in small buffers.
  • Other way to handle this, an application should only allow files of limited size(say 2MB).

Standard Options:

  • StandardOpenOptions gives full control over the operations on the file. Whether we want to override the file, whether we want to append or override the new content, whether we want to delete the file after using it, etc.,
Path newFilePath = Paths.get("c:/demo/dummy.txt");

//Create a new file only if the file does not exist, Append the text, open the file with write access
Files.write(newFilePath, "This is a dummy text".getBytes(StandardCharsets.UTF_8) ,
                                StandardOpenOption.CREATE, 
                                StandardOpenOption.APPEND, 
                                StandardOpenOption.WRITE);


Move and Delete:

  • Files.move(oldFilePath, newFilePath) and Files.delete(newFilePath) are for move and delete.

List files in a directory

Path newFileDirPath = Paths.get("c:/demo/");

// recursively list all the directories and files for a given directory

try(Stream<Path> walk = Files.walk(newFileDirPath)) {

    walk.sorted(Comparator.reverseOrder()).forEach(System.out::println); 
}

Files.list(newFileDirPath); //List only current directory files and directories

  • WatchService - For monitoring a directory or file for changes.

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