JavaIO

    public static void main(String[] args) {
        FileInputStream fis=null;
        try {

            fis=new FileInputStream("D:\\File\\data.txt");
//            循环读
            int i=0;
            while ((i=fis.read())!=-1){
                System.out.println(i);
            }

            System.out.println("=========");

            byte[] bytes=new byte[fis.available()];
            int read = fis.read(bytes);  //返回读取到字节数量
            System.out.println(read);
            System.out.println(new String(bytes));

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

public static void main(String[] args) {
    FileOutputStream fos=null;
    try {
        fos = new FileOutputStream("D:\\File\\dataout.txt");
        String str="Hello 你好！";
        byte[] bytes = str.getBytes();
        fos.write(bytes);
        fos.flush();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (fos != null) {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}