Java IO

IO(输入输出)是所有程序员必需的——输入，程序读取外部数据；输出，将程序数据输出到磁盘、光盘等。

Java的IO包下主要包括输入、输出两种IO流，每种输入、输出流又可以分为字节流和字符流。字节流是以字节为单位处理输入、输出操作；字符流是以字符为单位处理输入、输出操作。

Java的IO流使用了一种“装饰器设计模式”，它将IO流分成底层节点流和上层处理流，其中节点流用于和底层的物理存储节点直接关联——不同的物理节点获取的节点流的方式可能存在一定的差异，但程序可以把不同的物理节点流包装成统一的处理流，从而允许程序使用统一的输入、输出代码来读取不同的物理存储节点的资源。

Java 7 在java.nio及其子包下提供了一系列全新的API，这些API是对原有新IO的升级，因此被称为NIO2,通过这些NIO2, 程序可以更高效的进行输入、输出操作

public  class MyFile {
    
    @Test
    public  void fileNameFilter(){
         // 表示当前路径 
        File file = new File("." );
        System.out.println(file.getAbsolutePath());
        String [] nameList = file.list((dir,name)->name.endsWith(".java") || new File(name).isDirectory());
         for (String name:nameList){
            System.out.println(name);
        }
    }
    
    @Test
    public  void operateDir(){
        String filePath = "D:/rding/testfile3/" ;
        File file = new File(filePath);
         boolean canMkdir = file.mkdir();
        System.out.println(canMkdir);
        File dirs = new File("d:/rding/testfile3/test31/test32" );
        dirs.mkdirs();
        File roots[] = File.listRoots();
         for ( int i = 0; i < roots.length;i++ ){
            System.out.println(roots[i]);
        }
        
    }

    @Test
    public  void operateFile(){
        String filepath = "D:/rding/testfile2/file1.txt" ;
        File file = new File(filepath);
         boolean createNewFile;
         try {
            createNewFile = file.createNewFile();
            System.out.println(createNewFile);
            // 生成一个文件，文件名是前缀+随机数+后缀名 
            File tempFile = File.createTempFile("Hello", ".java", new File("D:/rding/testfile2/" ));
            File delteFile = new File("D:/rding/testfile2/file2.txt" );
             boolean deleteFile = delteFile.delete();
            System.out.println(delteFile);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    @Test
    public  void fileContent(){
        String filePath = "D:/rding/testfile2/file.txt" ;
        File file = new File(filePath);
         long length = file.length();
        System.out.println(length);
        Date lastModified = new Date(file.lastModified());
        System.out.println(lastModified);
    }
    
    @Test
    public  void fileName() {
        String filePath = "D:/rng/testfile1" ;
        File file = new File(filePath);
        String fileName = file.getName();
        System.out.println( "fileName : " + fileName);
        String path = file.getPath();
        System.out.println( "path : " + path);
        String absolutePath = file.getAbsolutePath();
        System.out.println( "absolutePath : " + absolutePath);
        File absoluteFile = file.getAbsoluteFile();
        System.out.println( "absoluteFile : " + absoluteFile);
        File parentFile = file.getParentFile();
        System.out.println( "parentFile : " + parentFile);
        String parentPath = file.getParent();
        System.out.println( "parentPath : " + parentPath);
         boolean canRenameToFile = file.renameTo( new File("D:/rding/testfile2" ));
        System.out.println( "canRename : " + canRenameToFile);
    }

    @Test
    public  void checkFile() {
        String filePath = "D:/rding/testfile" ;
        File file = new File(filePath);
         boolean exists = file.exists();
        System.out.println( "exists : " + exists);
         boolean canWrite = file.canWrite();
        System.out.println( "canWrite : " + canWrite);
         boolean canRead = file.canRead();
        System.out.println( "canRead : " + canRead);
         boolean isFile = file.isFile();
        System.out.println( "isFile : " + isFile);
         boolean isDirectory = file.isDirectory();
        System.out.println( "isDirectory ： " + isDirectory);
         boolean isAbsolute = file.isAbsolute();
        System.out.println( "isAbsolute : " + isAbsolute);
    }
}