每日一词——IO + NIO + NIO2

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IO

以字节、字符为单位进行低逼格的处理：通过InputStream || Reader 连接 source，通过 OutoutStream || Writer 连接 destination

NIO

以 缓存 为单位进行高逼格的处理：通过 Chanel 连接 source 及 destination

NIO2

对文件系统进行了封装，开发者只需要使用抽象的接口，其内部实现交给各个文件系统的厂商来实现，所以 java 的包分两类，一类供开发者使用：java.nio.file, java.nio.file.attribute，一类供厂商使用：java.nio.file.spi

3段代码演示其核心思想（其实也可以看出来他们的确是越来越看起来简单）

IO核心代码

    public static void save(Reader src, Writer dest) {
        try(Reader input = src;Writer output = dest) {
            int length = -1;
            char[] data = new char[1024];
            while ((length = input.read(data)) != -1) 
                output.write(data, 0, length);
        } catch (IOException e) {
            logger.info("错误信息:{}", e.getMessage());
        }
    }

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NIO核心代码块

    public void dump(ReadableByteChannel src, WritableByteChannel dest) {
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        try(ReadableByteChannel srcCH = src; WritableByteChannel destCH = dest) {
            buffer.flip();  // position = 0; limit = buffer当前元素数量
            destCH.write(buffer);
            buffer.clear(); // postion = 0; limit = buffer容量
        } catch (IOException e) {
            logger.info(e.getMessage());
        }
    }

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不难看出，IO相比较NIO，多了一个 int length, 记录每次有多少元素被读到

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NIO2 核心代码
1、操作路径：Path path = Path.get(System.getProperty(“user.home”, “Document”, “Downloads”);
2、属性读取：BasicFileAttributes attrs = Files.readAttributes(file, BasicFileAttributes.class);
3、属性赋值：Files.setAttribute(Paths.get(“C:\workspace\Main.java”, “basic:lastModifiedTime”, FileTime.fromMillis(System.currentTimeMillis()));
4、操作文档：
1)Files.copy(srcPath, destPath, StandardCopyOption.REPLACE_EXISTING
2)BufferedReader reader = Files.newBufferedReader(filePath, “UTF-8”);
instead of
BufferedReader reader = new BufferedReader(
new InputStreamReader(
new FileInputStream(file, “UTF-8”)));

Path: An object that may be used to locate a file in a file system.

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DirectoryStream: A directory stream allows for the convenient use of the for-each construct to iterate over adirectory.

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FileSystem: This class defines the {@link #getDefault getDefault} method to get the default file system and factory methods to construct other types of file systems.

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Files: This class consists exclusively of static methods that operate on files, directories, or other types of files.