Paths和Files

一、Path

jdk7 引入了 Path 和 Paths 类，Path 用来表示文件路径，Paths 是工具类，用来获取 Path 实例

1、相对路径定位 test.txt

Path source = Paths.get("test.txt");

2、绝对路径定位 d:\test.txt

Path source = Paths.get("d:\\test.txt");

3、绝对路径定位d:\data\test

Path path = Paths.get("d:\\data", "test");

二、Files

1、检查文件是否存在

Path path = Paths.get("src/main/resource/nio/test2.txt");
boolean exists = Files.exists(path);

2、创建目录

Path path = Paths.get("src/main/resource/nio/test");
Files.createDirectory(path);

在src/main/resource/nio目录下创建新目录test

注意：

（1）如果目录已存在，会抛异常 FileAlreadyExistsException

（2）不能一次创建多级目录，否则会抛异常 NoSuchFileException

3、创建多级目录用

Path path = Paths.get("src/main/resource/nio/first/second");
Files.createDirectory(path);

4、复制文件

Path fromPath = Paths.get("src/main/resource/nio/test2.txt");

Path toPath = Paths.get("src/main/resource/nio/to.txt");

Files.copy(fromPath,toPath, StandardCopyOption.REPLACE_EXISTING);

如果希望用 source 覆盖掉 target，需要用 StandardCopyOption 来控制

5、移动文件

Path fromPath = Paths.get("src/main/resource/nio/test2.txt");

Path toPath = Paths.get("src/main/resource/nio/to2.txt");

Files.move(fromPath,toPath,StandardCopyOption.ATOMIC_MOVE);

StandardCopyOption.ATOMIC_MOVE 保证文件移动的原子性

6、删除文件

Path path = Paths.get("src/main/resource/nio/to.txt");

Files.delete(path);

如果文件不存在，会抛异常 NoSuchFileException

7、删除目录

Path path = Paths.get("src/main/resource/nio/test");

Files.delete(path);

8、遍历目录

Path path = Paths.get("src/main/resource/nio");

Files.walkFileTree(path,new SimpleFileVisitor<Path>(){
	//访问文件前处理
	@Override
	public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
		System.out.println("before dir="+dir);
		return super.preVisitDirectory(dir, attrs);
	}

	//访问文件处理
	@Override
	public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
		System.out.println(file);
		return super.visitFile(file, attrs);
	}

	//访问文件后处理
	@Override
	public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
		System.out.println("after dir="+dir);
		return super.postVisitDirectory(dir, exc);
	}

	//访问文件失败处理
	@Override
	public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
		System.out.println("exception file="+file);
		return super.visitFileFailed(file, exc);
	}
});

before dir=src\main\resource\nio
src\main\resource\nio\test.txt
src\main\resource\nio\test2.txt
after dir=src\main\resource\nio

三、两个 Channel 传输数据

String FROM = "helloword/data.txt";
String TO = "helloword/to.txt";
long start = System.nanoTime();
try (
     FileChannel from = new FileInputStream(FROM).getChannel();
     FileChannel to = new FileOutputStream(TO).getChannel();
    ) {
    from.transferTo(0, from.size(), to);
} catch (IOException e) {
    e.printStackTrace();
}
long end = System.nanoTime();
System.out.println("transferTo 用时：" + (end - start) / 1000_000.0);

超过 2g 大小的文件传输

public class TestFileChannelTransferTo {
    public static void main(String[] args) {
        try (
                FileChannel from = new FileInputStream("data.txt").getChannel();
                FileChannel to = new FileOutputStream("to.txt").getChannel();
        ) {
            // 效率高，底层会利用操作系统的零拷贝进行优化
            long size = from.size();
            // left 变量代表还剩余多少字节
            for (long left = size; left > 0; ) {
                System.out.println("position:" + (size - left) + " left:" + left);
                left -= from.transferTo((size - left), left, to);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}