Java 复制大文件方式FileChannel 用法 |
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Java 复制大文件方式FileChannel 用法
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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 ByteBufferFileChannel 和直接模式的 ByteBufferFileChannel.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： 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); } } }
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： 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： 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： 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： |
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