Java 复制大文件方式（nio2 FileChannel 拷贝文件能力测试）

目前为止，我们已经学习了很多 Java 拷贝文件的方式，除了 FileChannel 提供的方法外，还包括使用 Files.copy() 或使用字节数组的缓冲/非缓冲流。那个才是最好的选择呢？这个问题很难回答，因为答案基于很多因素。本文将目光集中到一个因素，那就是速度，因为拷贝任务 越快将会提高效率，在有些情况下，这是成功的关键。因此，本文将使用一个应用程序来比较下面这些拷贝方式的具体时间：

• • 
    
• FileChannel 和非直接模式的 ByteBuffer
• FileChannel 和直接模式的 ByteBuffer
• FileChannel.transferTo()
• FileChannel.transferFrom()
• FileChannel.map()
• 使用字节数组和缓冲流
• 使用字节数组和非缓冲流
• File.copy()（Path 到 Path，InputStream 到 Path 和 Path 到 OutputStream）
  • 
    

应用程序基于下面的条件：

• • 
    
• 拷贝文件类型 MP4 视频（文件名为 Rafa Best Shots.mp4，所在目录为 C:\rafaelnadal\tournaments\2009\videos）
• 文件大小：58.3MB
• 测试的缓冲区大小：4KB, 16KB, 32KB, 64KB, 128KB, 256KB, and 1024KB
• 机器配置：Mobile AMD Sempron Processor 3400 + 1.80 GHz, 1.00GB RAM, 32-bit
  OS, Windows 7 Ultimate
• 测量类型：使用 System.nanoTime() 方法
• 连续运行三次后再获取时间；前三次运行将会被忽略。开始运行的时间总会比后面运行的时间要长一些。
  • 
    

下面将列出完整的应用程序：

import java.nio.MappedByteBuffer; import java.io.OutputStream; import java.io.InputStream; import java.io.BufferedInputStream; import java.io.BufferedOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; import java.util.EnumSet; import static java.nio.file.LinkOption.NOFOLLOW_LINKS;   public class Main {    public static void deleteCopied(Path path){             try {       Files.deleteIfExists(path);   } catch (IOException ex) {     System.err.println(ex);   }            }        public static void main(String[] args) {    final Path copy_from = Paths.get("C:/rafaelnadal/tournaments/2009/videos/                                                                         Rafa Best Shots.mp4");  final Path copy_to = Paths.get("C:/Rafa Best Shots.mp4");  long startTime, elapsedTime;  int bufferSizeKB = 4; //also tested for 16, 32, 64, 128, 256 and 1024  int bufferSize = bufferSizeKB * 1024;    deleteCopied(copy_to);    //FileChannel and non-direct buffer  System.out.println("Using FileChannel and non-direct buffer ...");  try (FileChannel fileChannel_from = (FileChannel.open(copy_from,                         EnumSet.of(StandardOpenOption.READ)));       FileChannel fileChannel_to = (FileChannel.open(copy_to,                         EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)))) {                     startTime = System.nanoTime();                     // Allocate a non-direct ByteBuffer       ByteBuffer bytebuffer = ByteBuffer.allocate(bufferSize);         // Read data from file into ByteBuffer       int bytesCount;       while ((bytesCount = fileChannel_from.read(bytebuffer)) > 0) {        //flip the buffer which set the limit to current position, and position to 0                      bytebuffer.flip();        //write data from ByteBuffer to file        fileChannel_to.write(bytebuffer);        //for the next read        bytebuffer.clear();       }               elapsedTime = System.nanoTime() - startTime;       System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds");  } catch (IOException ex) {    System.err.println(ex);  }    deleteCopied(copy_to);    //FileChannel and direct buffer  System.out.println("Using FileChannel and direct buffer ...");  try (FileChannel fileChannel_from = (FileChannel.open(copy_from,                         EnumSet.of(StandardOpenOption.READ)));       FileChannel fileChannel_to = (FileChannel.open(copy_to,                         EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)))) {                     startTime = System.nanoTime();                     // Allocate a direct ByteBuffer       ByteBuffer bytebuffer = ByteBuffer.allocateDirect(bufferSize);         // Read data from file into ByteBuffer       int bytesCount;       while ((bytesCount = fileChannel_from.read(bytebuffer)) > 0) {        //flip the buffer which set the limit to current position, and position to 0                      bytebuffer.flip();        //write data from ByteBuffer to file        fileChannel_to.write(bytebuffer);        //for the next read        bytebuffer.clear();       }               elapsedTime = System.nanoTime() - startTime;       System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds");  } catch (IOException ex) {    System.err.println(ex);  }    deleteCopied(copy_to);    //FileChannel.transferTo()  System.out.println("Using FileChannel.transferTo method ...");  try (FileChannel fileChannel_from = (FileChannel.open(copy_from,                         EnumSet.of(StandardOpenOption.READ)));       FileChannel fileChannel_to = (FileChannel.open(copy_to,                         EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)))) {         startTime = System.nanoTime();         fileChannel_from.transferTo(0L, fileChannel_from.size(), fileChannel_to);         elapsedTime = System.nanoTime() - startTime;       System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds");  } catch (IOException ex) {    System.err.println(ex);  }    deleteCopied(copy_to);            //FileChannel.transferFrom()  System.out.println("Using FileChannel.transferFrom method ...");  try (FileChannel fileChannel_from = (FileChannel.open(copy_from,                          EnumSet.of(StandardOpenOption.READ)));       FileChannel fileChannel_to = (FileChannel.open(copy_to,                         EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)))) {         startTime = System.nanoTime();         fileChannel_to.transferFrom(fileChannel_from, 0L, (int) fileChannel_from.size());         elapsedTime = System.nanoTime() - startTime;       System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds");  } catch (IOException ex) {    System.err.println(ex);  }    deleteCopied(copy_to);                     //FileChannel.map  System.out.println("Using FileChannel.map method ...");  try (FileChannel fileChannel_from = (FileChannel.open(copy_from,                         EnumSet.of(StandardOpenOption.READ)));       FileChannel fileChannel_to = (FileChannel.open(copy_to,                         EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)))) {                               startTime = System.nanoTime();       MappedByteBuffer buffer = fileChannel_from.map(FileChannel.MapMode.READ_ONLY,                                                                     0, fileChannel_from.size());                                 fileChannel_to.write(buffer);       buffer.clear();         elapsedTime = System.nanoTime() - startTime;       System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); } catch (IOException ex) {   System.err.println(ex); }           deleteCopied(copy_to);                  //Buffered Stream I/O   System.out.println("Using buffered streams and byte array ...");   File inFileStr = copy_from.toFile(); File outFileStr = copy_to.toFile(); try (BufferedInputStream in = new BufferedInputStream(new FileInputStream(inFileStr));      BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFileStr))) {        startTime = System.nanoTime();        byte[] byteArray = new byte[bufferSize];      int bytesCount;      while ((bytesCount = in.read(byteArray)) != -1) {              out.write(byteArray, 0, bytesCount);      }        elapsedTime = System.nanoTime() - startTime;      System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); } catch (IOException ex) {   System.err.println(ex); }   deleteCopied(copy_to);   System.out.println("Using un-buffered streams and byte array ...");   try (FileInputStream in = new FileInputStream(inFileStr);      FileOutputStream out = new FileOutputStream(outFileStr)) {        startTime = System.nanoTime();        byte[] byteArray = new byte[bufferSize];      int bytesCount;      while ((bytesCount = in.read(byteArray)) != -1) {              out.write(byteArray, 0, bytesCount);      }        elapsedTime = System.nanoTime() - startTime;      System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); } catch (IOException ex) {   System.err.println(ex); }   deleteCopied(copy_to);   System.out.println("Using Files.copy (Path to Path) method ..."); try {     startTime = System.nanoTime();       Files.copy(copy_from, copy_to, NOFOLLOW_LINKS);       elapsedTime = System.nanoTime() - startTime;     System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); } catch (IOException e) {   System.err.println(e); }   deleteCopied(copy_to);   System.out.println("Using Files.copy (InputStream to Path) ..."); try (InputStream is = new FileInputStream(copy_from.toFile())) {       startTime = System.nanoTime();       Files.copy(is, copy_to);       elapsedTime = System.nanoTime() - startTime;     System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); } catch (IOException e) {   System.err.println(e); }   deleteCopied(copy_to);   System.out.println("Using Files.copy (Path to OutputStream) ..."); try (OutputStream os = new FileOutputStream(copy_to.toFile())) {        startTime = System.nanoTime();        Files.copy(copy_from, os);        elapsedTime = System.nanoTime() - startTime;      System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds");  } catch (IOException e) {    System.err.println(e);  }  } }

输出结果排序比较复杂，其中包含了很多数据。下面我将主要的对比用图形的方式展示出来。图形中 Y 坐标表示消耗的时间（单位：秒），X 坐标表示缓冲的大小（或运行次数，跳过了前三次运行）。

FileChannel 和非直接模式 Buffer vs. FileChannel 和直接模式 Buffer

从下图看来，如果缓存小于 256KB，那么非直接模式的 Buffer 快一点，而缓存大于 256KB 后，直接模式的 Buffer 快一点：

FileChannel.transferTo() vs. FileChannel.transferFrom() vs. FileChannel.map()

从下图看来，FileChannel.transferTo() 和 FileChannel.transferFrom 运行七次的速度都差不多，而 FileChannel.map 的速度就要差很多：

三种 Files.copy() 方法

从下图看来，最快的是 Path 到 Path，其次是 Path 到 OutputStream，最慢的是 InputStream 到 Path：

FileChannel 和非直接模式 Buffer vs. FileChannel.transferTo() vs. Path 到 Path

最后，我们将前面最快的三种方式综合起来比较。从比较的结果来看，似乎 Path 到 Path 是最快的解决方案：