为什么我复制文件比你快 java

IO流复制文件速度对比
目录

- IO流复制文件速度对比
- - 我们先以复制视频为例
  - - 准备工作
    - 首先上场的是`FileOutputStream`和`FileInputStream`
    - 接着上场的是`BufferedOutputStream`和`BufferedInputStream`
  - 接着我们用复制文本来比较
  - - 一：`FileInputStream`和`FileOutputStream`
    - 二：`BufferedInputStream`和`BufferedOutputStream`
    - 三 : `FileReader`和 `FileWriter`
    - 四 :`BufferedReader`和`BufferedWriter`

我们先以复制视频为例
IO流分类
准备工作

计时方法思路
System.currentTimeMillis()以毫秒为单位返回当前时间

long start = System.currentTimeMillis(); //调用复制方法 emthod01(); long end = System.currentTimeMillis(); System.out.println("共耗时" + (end - start) + "毫秒");

使用的视频大小

首先上场的是FileOutputStream和FileInputStream

我们先用一次读取一个字节的方法

public static void emthod01() throws IOException { FileOutputStream fos = new FileOutputStream("D:\\3022809742\\王者荣耀年度CG2.mp4"); FileInputStream fis = new FileInputStream("D:\\3022809742\\王者荣耀年度CG.mp4"); int by; while ((by = fis.read()) != -1) { fos.write(by); } fos.close(); fis.close(); }

结果

共耗时140475毫秒

竟然用了两分多钟，我一度以为我写错了

接着我们一次读取一个字节数组

public static void emthod02() throws IOException { FileOutputStream fos = new FileOutputStream("D:\\3022809742\\王者荣耀年度CG2.mp4"); FileInputStream fis = new FileInputStream("D:\\3022809742\\王者荣耀年度CG.mp4"); byte[] bytes = new byte[1024]; int len; while ((len = fis.read(bytes)) != -1) { fos.write(bytes, 0, len); } fos.close(); fis.close(); }

结果

共耗时211毫秒

接着上场的是BufferedOutputStream和BufferedInputStream

我们还是先试一下一次读取一个字节

public static void emthod03() throws IOException { BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("D:\\3022809742\\王者荣耀年度CG2.mp4")); BufferedInputStream bis = new BufferedInputStream(new FileInputStream("D:\\3022809742\\王者荣耀年度CG.mp4")); int by; while ((by = bis.read()) != -1) { bos.write(by); } bos.close(); bis.close(); }

结果

【为什么我复制文件比你快】共耗时349毫秒

接着用一次读取一个字节数组的方式

public static void emthod04() throws IOException { BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("D:\\3022809742\\王者荣耀年度CG2.mp4")); BufferedInputStream bis = new BufferedInputStream(new FileInputStream("D:\\3022809742\\王者荣耀年度CG.mp4")); byte[] bytes = new byte[1024]; int len; while ((len = bis.read(bytes)) != -1) { bos.write(bytes, 0, len); } bos.close(); bis.close(); }

结果

共耗时43毫秒

接着我们用复制文本来比较

我们先生成一个文本文件

//生成一个文件 public static void emthod() throws IOException { FileWriter fw = new FileWriter(new File("D:\\3022809742\\zjw.txt")); int i = 0; while (i < 1000000) { fw.write("好"); i++; } fw.close(); }

文件属性如下

一：FileInputStream和FileOutputStream

一次一个字符

public static void emthod1() throws IOException {FileInputStream fis = new FileInputStream("D:\\3022809742\\zjw.txt"); FileOutputStream fos = new FileOutputStream("D:\\3022809742\\zjw2.txt"); int by; while ((by = fis.read()) != -1) { fos.write(by); } fos.close(); fis.close(); }

结果（估计又是最慢的的）

共耗时16273毫秒

一次一个字节数组

public static void emthod2() throws IOException {FileInputStream fis = new FileInputStream("D:\\3022809742\\zjw.txt"); FileOutputStream fos = new FileOutputStream("D:\\3022809742\\zjw2.txt"); int len = 0; byte[] bytes = new byte[1024]; while ((len = fis.read(bytes)) != -1) { fos.write(bytes, 0, len); } fos.close(); fis.close(); }

结果

共耗时31毫秒

二：BufferedInputStream和BufferedOutputStream

一次一个字符
- 先关闭外层流bos和bis，再关闭内层流fis和fos
- 关闭外层流时，内层流自行关闭，所以只需要关闭外层流。

public static void emthod3() throws IOException {BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File("D:\\3022809742\\zjw.txt"))); BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("D:\\3022809742\\zjw2.txt"))); int by; while ((by = bis.read()) != -1) { bos.write(by); bos.flush(); }bis.close(); bos.close(); }

结果
产生这个结果的原因是

共耗时16273毫秒

一次一个字节数组

public static void emthod4() throws IOException {BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File("D:\\3022809742\\zjw.txt"))); BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("D:\\3022809742\\zjw2.txt"))); int len = 0; byte[] bytes = new byte[1024]; while ((len = bis.read(bytes)) != -1) { bos.write(bytes, 0, len); bos.flush(); } bis.close(); bos.close(); }

结果

共耗时28毫秒

三 : FileReader和 FileWriter

注意：FileReader和 FileWriter只能处理字符流
一次一个字符

public static void emthod5() throws IOException { FileReader fr = new FileReader(new File("D:\\3022809742\\zjw.txt")); FileWriter fw = new FileWriter(new File("D:\\3022809742\\zjw2.txt")); int by; while ((by = fr.read()) != -1) { fw.write(by); } fw.close(); fr.close(); }

结果

共耗时122毫秒

一次一个字符数组

public static void emthod6() throws IOException { FileReader fr = new FileReader(new File("D:\\3022809742\\zjw.txt")); FileWriter fw = new FileWriter(new File("D:\\3022809742\\zjw2.txt")); int len = 0; char[] chars = new char[1024]; while ((len = fr.read(chars)) != -1) { fw.write(chars, 0, len); } fw.close(); fr.close(); }

结果

共耗时66毫秒

四 :BufferedReader和BufferedWriter

BufferedReader除了继承了Reader类的方法之外，有自己的独有方法：
String readLine()：读取一行数据，终止符号：
换行（\n），回车（\r），\r\n(windows)
它的返回值包含改行的字符串，不包含任何终止符号，如果到达流末尾，返回null

一次一个字符

public static void emthod7() throws IOException {BufferedReader br = new BufferedReader(new FileReader(new File("D:\\3022809742\\zjw.txt"))); BufferedWriter bw = new BufferedWriter(new FileWriter(new File("D:\\3022809742\\zjw2.txt"))); int by; while ((by = br.read()) != -1) { bw.write(by); } //释放资源 br.close(); bw.close(); }

结果

共耗时80毫秒

一次一个字符数组

public static void emthod8() throws IOException {BufferedReader br = new BufferedReader(new FileReader(new File("D:\\3022809742\\zjw.txt"))); BufferedWriter bw = new BufferedWriter(new FileWriter(new File("D:\\3022809742\\zjw2.txt"))); char[] chars = new char[1024]; int len; while ((len = br.read(chars)) != -1) { new String(chars, 0, len); } //释放资源 br.close(); bw.close(); }

结果

共耗时49毫秒

特有方法

public static void emthod9() throws IOException {BufferedReader br = new BufferedReader(new FileReader(new File("D:\\3022809742\\zjw.txt"))); BufferedWriter bw = new BufferedWriter(new FileWriter(new File("D:\\3022809742\\zjw2.txt"))); String data; while ((data = https://www.it610.com/article/br.readLine()) != null) { bw.write(data); // 换行 bw.newLine(); } //释放资源 br.close(); bw.close(); }