Java零基础day20

• 一、缓冲的概念
• 二、IO流的分类
• • 1.字节输入输出流
  • 2.字符输入输出流
  • 综合案例

看视频有点卡？暂停一下，加载缓冲一下。

快递：送到物流中转站，然后分批次的发。物流中转站就是缓冲的概念。

IO流的本质就是对电脑的文件进行读和写的

计算机通过CPU内存读取磁盘上面的文件数据，一次读取1字节。但是可以加上缓冲的概念

每次读取4kb，效率会变高

package com.qfedu.fileoutstream;

import java.io.*;


public class Demo2 {
    public static void main(String[] args) throws IOException {
        long start = System.currentTimeMillis();
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(("F:/aaa/1.mp4")));

        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(("F:/aaa/bbb/1.mp4")));
        byte[] bytes = new byte[4 * 1024];
        int length;
        while ((length = bis.read(bytes)) != -1) {
            System.out.println("哈哈");
            bos.write(bytes, 0, length);
        }
        bos.close();
        bis.close();
        long end = System.currentTimeMillis();
        System.out.println(end - start);//324ms
        copyVideo();

    }

    public static void copyVideo() throws IOException {
        long start = System.currentTimeMillis();
        FileInputStream fis = new FileInputStream(("F:/aaa/1.mp4"));
        FileOutputStream fos = new FileOutputStream(("F:/aaa/bbb/1.mp4"));
        int length;
        while ((length = fis.read()) != -1) {
            System.out.println("哈哈");
            fos.write(length);
        }
        fos.close();
        fis.close();
        long end = System.currentTimeMillis();
        System.out.println(end - start);//444435ms
    }
}

FileReader:是一个阅读字符文件的便利类，是专门处理字符文件的，比如txt文件。

是从字节流到字符流的桥：它读取字节，并使用指定的charset将其解码为字符，它使用的字符集可以由名称指定，也可以被明确指定，或者可以接受平台的默认字符集

牵涉到解码，底层是字节流，但是会解码为字符。如果解码失败就意味着咱们读取失败了

一般不会使用字符流操作图片，音频，视频等，因为牵涉到解码。会出问题！！！开发一般使用字节流！！！

package com.qfedu.task;

import java.io.*;


public class Demo4 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(("F:/aaa/斗破苍穹.txt")));
        BufferedWriter bw = new BufferedWriter(new FileWriter(("F:/aaa/ccc/斗破苍穹.txt")));
        char[] chs = new char[4 * 1024];
        int length;
        while ((length = br.read(chs)) != -1) {
            bw.write(chs, 0, length);
        }
        bw.close();
        br.close();
    }
}

package com.qfedu.task;

import java.io.*;
import java.util.Scanner;


public class Demo5 {
    public static void main(String[] args) throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请选择使用方法1.字节IO流 2.字符IO流");
        int num = scanner.nextInt();
        long start = System.currentTimeMillis();
        if (num == 1) {
            txtOrMp3OrMp4Copy();
        } else if (num == 2) {
            txtCopy();
        } else {
            System.out.println("输入错误！！！");
        }
        long end = System.currentTimeMillis();
        System.out.println("复制成功，共用时" + (end - start) / 1000 + "秒");
    }

    //字节IO流
    public static void txtOrMp3OrMp4Copy() throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入需要复制的文件存放绝对路径");
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream((scanner.next())));
        System.out.println("请输入复制后的文件存放绝对路径");
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream((scanner.next())));
        byte[] bytes = new byte[4 * 1024];
        int length;
        while ((length = bis.read(bytes)) != -1) {
            bos.write(bytes, 0, length);
        }
        bos.close();
        bis.close();
    }

    //字符IO流
    public static void txtCopy() throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入需要复制的文件存放绝对路径");
        BufferedReader br = new BufferedReader(new FileReader((scanner.next())));
        System.out.println("请输入复制后的文件存放绝对路径");
        BufferedWriter bw = new BufferedWriter(new FileWriter((scanner.next())));
        char[] chs = new char[4 * 1024];
        int length;
        while ((length = br.read(chs)) != -1) {
            bw.write(chs, 0, length);
        }
        bw.close();
        br.close();
    }
}