Java粗浅认识-I/O（三）

Nio2

什么是Java Nio2，java Nio2是在java 7新增内容，在java1.4 nio的基础上再次对I/O模型的增强，新增Path类，Files工具类，Paths工具类，主要是为了方便文件、目录的操作。

java.nio.file.Path

一个Path代表了一个在本地文件系统的一个路径

1.创建一个path类

   /**
     * 创建一个Path类
     *
     * @throws URISyntaxException
     */
    private static void createPath() throws URISyntaxException {
        //1.根据文件名构建
        Path path = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\test.txt");
        System.out.println(path);
        //2.根据多个文件名，子文件名构建
        Path path1 = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test", "sub", "subTest.txt");
        System.out.println(path1);

        //3.根据统一资源定位符构建
        Path path2 = Paths.get(new URI("file:///C:/Users/baopz/Desktop/图片/test/uri.txt"));
        System.out.println(path2);

        //4.根据FileSystems创建
        Path path3 = FileSystems.getDefault().getPath("C:", "1.txt");
        System.out.println(path3);
    }

2.Path对象和File相互转换 Path对象转换为URI

   /**
     * Path对象和文件相互转换
     * path转换为uri
     */
    public static void convert() {
        //path转换为文件
        Path path = Paths.get("c://1.txt");
        System.out.println(path);
        File file = path.toFile();
        System.out.println(file.getAbsolutePath());

        //文件转换为path
        File file1 = new File("C://1.txt");
        System.out.println(file1);
        Path path1 = file1.toPath();
        System.out.println(path1);

        //path转换为uri
        URI uri = path1.toUri();
        System.out.println(uri);
    }

3.创建孩子节点，创建兄弟节点

    /**
     * 创建孩子节点，创建兄弟节点
     */
    public static void resolve() {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test");
        //创建孩子节点
        Path child = current.resolve("child");
        System.out.println(child);

        //创建兄弟节点
        Path brother = current.resolveSibling("brother");
        System.out.println(brother);
    }

4.得到文件名，以及Path类的计算操作

   /**
     * path结构，root/0/1/2/..,count不会计算root层,根节点的parent是null
     * 截取部分subPath [start,end)，包含start的下标，不包含end的下标
     */
    public static void getFilename() {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\1.txt");
        Path filename = current.getFileName();
        System.out.println(filename.toString());

        //根据计算得到文件名
        filename = current.getName(current.getNameCount() - 1);
        System.out.println(filename.toString());

        //得到根节点
        System.out.println(current.getRoot());

        //打印每一层的filename
        for (int i = 0; i < current.getNameCount(); i++) {
            System.out.println(i + "层 " + current.getName(i));
        }

        //根节点的父亲节点是null
        System.out.println(current.getRoot().getParent());

        //截取部分path[start,end)
        System.out.println(current.subpath(1,3));

        //是不是以1.txt结尾的path，注意这里不能用来判断是不是某种格式结尾，这里计算的最后一个节点
        //这里返回的是true
        System.out.println(current.endsWith("1.txt"));
        //这里返回的是false
        System.out.println(current.endsWith(".txt"));
    }

5.regex或者glob匹配

    /**
     * regex或者glob匹配
     * 匹配语法
     * 语法:模式 => {regex|glob}:pattern
     */
    public static void match() {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\1.txt");
        FileSystem fileSystem =  FileSystems.getDefault();
        //正则表达式匹配.txt结尾
        PathMatcher pathMatcher = fileSystem.getPathMatcher("regex:.*.txt");
        System.out.println(pathMatcher.matches(current));

        //glob匹配.txt结尾
        pathMatcher = fileSystem.getPathMatcher("glob:*.txt");
        System.out.println(pathMatcher.matches(current));
        
    }

6.java.nio.file.WatchService监控器

这个功能还是非常实用的，文件监控器，可以监控文件以及目录的变化,以及设置监控频率，这里是演示，会运行在main线程里面，项目中建议开个线程单独运行，（后面我会吧线程的相关操作列出来）。

    /**
     * 文件监控器，可以监控文件以及目录的变化,以及设置监控频率
     */
    public static void watchServer() throws IOException, InterruptedException {
        FileSystem fileSystem = FileSystems.getDefault();
        WatchService watchService = fileSystem.newWatchService();

        Path path = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test");
        //监控事件，新增，修改，删除，溢出，监控频率=low
        path.register(watchService,new WatchEvent.Kind<?>[]{StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE,
                StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.OVERFLOW},
                SensitivityWatchEventModifier.LOW);
        while (true) {
            WatchKey watchKey = watchService.take();
            for (WatchEvent<?> watchEvent : watchKey.pollEvents()) {
                //有新文件创建
                if (watchEvent.kind() == StandardWatchEventKinds.ENTRY_CREATE) {
                    Path path1 = (Path) watchEvent.context();
                    System.out.println("新建了一个文件：" + path1);
                }
                //有文件被删除
                if(watchEvent.kind()==StandardWatchEventKinds.ENTRY_DELETE){
                    Path path1 = (Path) watchEvent.context();
                    System.out.println("删除了一个文件：" + path1);
                }

                if (watchEvent.kind()==StandardWatchEventKinds.ENTRY_MODIFY){
                    Path path1 = (Path) watchEvent.context();
                    System.out.println("文件被修改:"+path1);
                }

                if (watchEvent.kind()==StandardWatchEventKinds.OVERFLOW){
                    System.out.println("溢出");
                }
            }
            boolean valid = watchKey.reset();
            if (!valid) {
                break;
            }
        }
    }

java.nio.file.Files、java.nio.file.FileSystems工具类

1.创建文件

    public static void createFile() throws IOException {
        Path path = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\test.txt");
        //得到上一层节点
        Path parent = path.getParent();
        if (Files.notExists(parent)) {
            Files.createDirectories(parent);
        }
        //在创建文件的时候，一定要先存着上一层的目录
        if (Files.notExists(path)) {
            Files.createFile(path);
        }
    }

2.删除文件

    public static void delete() throws IOException {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\1.txt");
        boolean isSuccess = Files.deleteIfExists(current);
        System.out.println(isSuccess);
    }

3.得到BufferedReader，进行字符操作

   /**
     * 字符集对应不上会抛错
     * @throws IOException
     */
    public static void readBuffer() throws IOException {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test\\1.txt");
        BufferedReader bufferedReader = Files.newBufferedReader(current, Charset.forName("gbk"));
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            System.out.println(line);
        }
        bufferedReader.close();
    }

4.列出当前文件夹下所有文件

    /**
     * 列出当前目录下所有文件
     * @throws IOException
     */
    public static void listFile() throws IOException {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test");
        DirectoryStream directoryStream = Files.newDirectoryStream(current);
        for (Object aDirectoryStream : directoryStream) {
            System.out.println(aDirectoryStream);
        }
    }

5.树遍历

public static void walkingTheFileTree() throws IOException {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test");
        Set<FileVisitOption> visitOptions = new HashSet<>();
        visitOptions.add(FileVisitOption.FOLLOW_LINKS);
        //设置开始节点，访问操作，最大访问深度，具体访问操作
        Files.walkFileTree(current, visitOptions, 3, new MyFileVisitor());
    }

    public static class MyFileVisitor implements FileVisitor<Path> {

        @Override
        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
            System.out.println("访问文件夹之前操作。" + dir);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
            System.out.println("访问当前文件:" + file);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
            System.out.println("访问文件错误：" + file);
            //跳过sub
            return FileVisitResult.SKIP_SUBTREE;
        }

        @Override
        public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
            System.out.println("访问文件夹之后操作：" + dir);
            return FileVisitResult.CONTINUE;
        }
    }

6.文件属性，以及文件操作

public static void accessFile() throws IOException {
        Path current = Paths.get("C:\\Users\\baopz\\Desktop\\图片\\test");
        FileSystem fileSystem = FileSystems.getDefault();
        //遍历文件支持的所有视图
        for (String s : fileSystem.supportedFileAttributeViews()) {
            System.out.println(s);
        }

        //basic视图
        BasicFileAttributes basicFileAttributes =  Files.readAttributes(current,BasicFileAttributes.class);
        System.out.println(basicFileAttributes.lastModifiedTime());

        //dos视图
        DosFileAttributes dosFileAttributes = Files.readAttributes(current,DosFileAttributes.class);
        System.out.println(dosFileAttributes.isHidden());

        //复制
        Files.copy(current,current.resolve("副本"));
    }

到目前为止，java1.7 的Nio2已经写完了，接下来会讲解关于网络通信，还有一个异步通道会在下一章开头讲，会提一下Netty，再之后会针对Netty做专题详细讲解。