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

浅浅的花香味﹌ 2022-05-17 05:28 190阅读 0赞

*   *  文件操作
     *  WatchService

## **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);
        }
    }