Java 复制大文件方式FileChannel 用法

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:

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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:

Java 复制大文件方式FileChannel 用法_第1张图片

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:

Java 复制大文件方式FileChannel 用法_第2张图片

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:

Java 复制大文件方式FileChannel 用法_第3张图片

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:

Java 复制大文件方式FileChannel 用法_第4张图片


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