Java Language File I/O Migrating from java.io.File to Java 7 NIO (java.nio.file.Path)
Example
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... 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);
}
}
}
