Java 複製大文件方式FileChannel 用法

目前爲止，我們已經學習了很多 Java 拷貝文件的方式，除了 FileChannel 提供的方法外，還包括使用 Files.copy() 或使用字節數組的緩衝/非緩衝流。那個纔是最好的選擇呢？這個問題很難回答，因爲答案基於很多因素。本文將目光集中到一個因素，那就是速度，因爲拷貝任務 越快將會提高效率，在有些情況下，這是成功的關鍵。因此，本文將使用一個應用程序來比較下面這些拷貝方式的具體時間：

• FileChannel 和非直接模式的 ByteBuffer
• FileChannel 和直接模式的 ByteBuffer
• FileChannel.transferTo()
• FileChannel.transferFrom()
• FileChannel.map()
• 使用字節數組和緩衝流
• 使用字節數組和非緩衝流
• File.copy()（Path 到 Path，InputStream 到 Path 和 Path 到 OutputStream）

應用程序基於下面的條件：

• 拷貝文件類型 MP4 視頻（文件名爲 Rafa Best Shots.mp4，所在目錄爲 C:\rafaelnadal\tournaments\2009\videos）
• 文件大小：58.3MB
• 測試的緩衝區大小：4KB, 16KB, 32KB, 64KB, 128KB, 256KB, and 1024KB
• 機器配置：Mobile AMD Sempron Processor 3400 + 1.80 GHz, 1.00GB RAM, 32-bit
  OS, Windows 7 Ultimate
• 測量類型：使用 System.nanoTime() 方法
• 連續運行三次後再獲取時間；前三次運行將會被忽略。開始運行的時間總會比後面運行的時間要長一些。

下面將列出完整的應用程序：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249

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);  }  } }

 

輸出結果排序比較複雜，其中包含了很多數據。下面我將主要的對比用圖形的方式展示出來。圖形中 Y 座標表示消耗的時間（單位：秒），X 座標表示緩衝的大小（或運行次數，跳過了前三次運行）。

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

從下圖看來，如果緩存小於 256KB，那麼非直接模式的 Buffer 快一點，而緩存大於 256KB 後，直接模式的 Buffer 快一點：

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

從下圖看來，FileChannel.transferTo() 和 FileChannel.transferFrom 運行七次的速度都差不多，而 FileChannel.map 的速度就要差很多：

三種 Files.copy() 方法

從下圖看來，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

最後，我們將前面最快的三種方式綜合起來比較。從比較的結果來看，似乎 Path 到 Path 是最快的解決方案：