Java8新特性一点通 | 回顾文件操作和watchService文件变更监视操作

文件操作

今天重温了一些文件操作：
- Files.list() 遍历文件和目录

//List all files and sub-directories using Files.list()
        try {
            Files.list(Paths.get(".")).forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }

• Files.newDirectoryStream() 遍历文件和目录

//List files and sub-directories with Files.newDirectoryStream()
try {
            Files.newDirectoryStream(Paths.get(".")).forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }

• Files::isReularFile 找出目录中的文件

 //List only files inside directory using filter expression
        try {
            Files.list(Paths.get(".")).filter(Files::isRegularFile).forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }

• file->file.isHidden() 找出隐藏文件

 //Find all hidden files in directory
        final File[] files = new File(".").listFiles(file->file.isHidden());
        for(File file:files){
            System.out.println(file.getName());
        }

• Files.newBufferedWriter 迅速创建一个BufferedWriter，可以使编码语法更简洁

 //Write to file using BufferedWriter
        Path path  = Paths.get("D:\\test.txt");
        try(BufferedWriter writer = Files.newBufferedWriter(path)){
                writer.write("Hello World!");
        } catch (IOException e) {
            e.printStackTrace();
        }

• Files.write() 使用简介的语法写入内容到文件

 //Write to file using Files.write()
        try {
            Files.write(Paths.get("D:\\test1.txt"),"Hello".getBytes());
        } catch (IOException e) {
            e.printStackTrace();
        }

Tips：
对于比较大文件夹,使用DirectoryStream 会性能更好

---

WatchService

利用WatchService 对文件目录进行监视，可以对目录中增删改查这些动作进行监控

public class WatchServiceExample2 {

    public static void main(String[] args) throws IOException {

        Path curPath = Paths.get(".");

        WatchService watchService = curPath.getFileSystem().newWatchService();
        //遍历并注册目录
        walkAndRegisterDirectories(curPath, watchService);
        try {
            //监听目录变化
            while (true) {
                WatchKey watchKey = watchService.take();
                for (WatchEvent event : watchKey.pollEvents()) {
                    System.out.println(event.kind());
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

    private static void walkAndRegisterDirectories(Path path, WatchService watchService) throws IOException {
        Files.walkFileTree(path, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
                registerDirectory(dir, watchService);
                return FileVisitResult.CONTINUE;
            }
        });
    }

    private static void registerDirectory(Path dir, WatchService watchService) throws IOException {
        WatchKey key =  dir.register(watchService, StandardWatchEventKinds.ENTRY_CREATE
                , StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
    }
}