Migrating from java.io.File to Java 7 NIO

File I/O

Java I/O (Input and Output) is used to process the input and produce the output. Java uses the concept of stream to make I/O operation fast. The java.io package contains all the classes required for input and output operations. Handling files is also done in java by Java I/O API.

Migrating from java.io.File to Java 7 NIO (java.nio.file.Path)

These examples assume that you already know what Java 7's NIO is in general, and you are used to writing code using java.io.File. Use these examples as a means to quickly find more NIO-centric documentation for migrating.

There is much more to Java 7's NIO such as memory-mapped files or opening a ZIP or JAR file using FileSystem. These examples will only cover a limited number of basic use cases..

As a basic rule, if you are used to perform a file system read/write operation using a java.io.File instance method, you will find it as a static method within java.nio.file.Files.

Point to a path

// -> IO
File file = new File("io.txt");
 
// -> NIO
Path path = Paths.get("nio.txt");

Paths relative to another path

// Forward slashes can be used in place of backslashes even on a Windows operating system
// -> IO
File folder = new File("C:/");
File fileInFolder = new File(folder, "io.txt");
 
// -> NIO
Path directory = Paths.get("C:/");
Path pathInDirectory = directory.resolve("nio.txt");

Converting File from/to Path for use with libraries

// -> IO to NIO
Path pathFromFile = new File("io.txt").toPath();
 
// -> NIO to IO
File fileFromPath = Paths.get("nio.txt").toFile();

Check if the file exists and delete it if it does

// -> IO
if (file.exists()) {
     boolean deleted = file.delete();
     if (!deleted) {
           throw new IOException("Unable to delete file");
     }
}
 
// -> NIO
Files.deleteIfExists(path);

Write to a file via an OutputStream

There are several ways to write and read from a file using NIO for different performance and memory constraints, readability and use cases, such as FileChannel, Files.write(Path path, byte\[\] bytes, OpenOption... GoalKicker.com – Java® Notes for Professionals 451 options)... In this example, only OutputStream is covered, but you are strongly encouraged to learn about memory-mapped files and the various static methods available in java.nio.file.Files.

List<String> lines = Arrays.asList(
	String.valueOf(Calendar.getInstance().getTimeInMillis()),
	"line one",
	"line two");
 
// -> IO
if (file.exists()) {
	// Note: Not atomic
	throw new IOException("File already exists");
}
try (FileOutputStream outputStream = new FileOutputStream(file)) {
	for (String line : lines) {
		outputStream.write((line + System.lineSeparator()).getBytes(StandardCharsets.UTF_8));
	}
}
 
// -> NIO
try (OutputStream outputStream = Files.newOutputStream(path, StandardOpenOption.CREATE_NEW)) {
	for (String line : lines) {
		outputStream.write((line + System.lineSeparator()).getBytes(StandardCharsets.UTF_8));
	}
}

Iterating on each file within a folder

// -> IO
for (File selectedFile : folder.listFiles()) {
	// Note: Depending on the number of files in the directory folder.listFiles() may take a long 	time to return
	System.out.println((selectedFile.isDirectory() ? "d" : "f") + " " + 	selectedFile.getAbsolutePath());
}
 
// -> NIO
Files.walkFileTree(directory, EnumSet.noneOf(FileVisitOption.class), 1, new
SimpleFileVisitor<Path>() {
	@Override
	public FileVisitResult preVisitDirectory(Path selectedPath, BasicFileAttributes attrs) throws
	IOException {
		System.out.println("d " + selectedPath.toAbsolutePath());
		return FileVisitResult.CONTINUE;
	}
 
	@Override
	public FileVisitResult visitFile(Path selectedPath, BasicFileAttributes attrs) throws
	IOException {
		System.out.println("f " + selectedPath.toAbsolutePath());
		return FileVisitResult.CONTINUE;
	}
});

Recursive folder iteration

// -> IO
recurseFolder(folder);
 
// -> NIO
// Note: Symbolic links are NOT followed unless explicitly passed as an argument to
Files.walkFileTree
Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
	@Override
	public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws 	IOException {
		System.out.println("d " + selectedPath.toAbsolutePath());
		return FileVisitResult.CONTINUE;
	}
 
	@Override
	public FileVisitResult visitFile(Path selectedPath, BasicFileAttributes attrs) throws 	IOException {
		System.out.println("f " + selectedPath.toAbsolutePath());
		return FileVisitResult.CONTINUE;
	}
});
 
private static void recurseFolder(File folder) {
	for (File selectedFile : folder.listFiles()) {
		System.out.println((selectedFile.isDirectory() ? "d" : "f") + " " + selectedFile.getAbsolutePath());
		if (selectedFile.isDirectory()) {
		// Note: Symbolic links are followed
			recurseFolder(selectedFile);
		}
	}
}

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