Java 複製大檔案方式（nio2 FileChannel 拷貝檔案能力測試）
阿新 • • 發佈：2019-02-18
Java 拷貝檔案的方式很多，除了 FileChannel 提供的方法外，還包括使用 Files.copy() 或使用位元組陣列的緩衝/非緩衝流。那個才是最好的選擇呢？這個問題很難回答，因為答案基於很多因素。本文將目光集中到一個因素，那就是速度，因為拷貝任務 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式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()
- 使用位元組陣列和緩衝流
- 使用位元組陣列和非緩衝流
- File.copy()（Path 到 Path，InputStream 到 Path 和 Path 到 OutputStream）
應用程式基於下面的條件：
- 拷貝檔案型別 MP4 視訊（檔名為 Rafa Best Shots.mp4，所在目錄為 C:\rafaelnadal\tournaments\2009\videos）
- 檔案大小：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 - 測量型別：使用 System.nanoTime() 方法
- 連續執行三次後再獲取時間；前三次執行將會被忽略。開始執行的時間總會比後面執行的時間要長一些。
下面將列出完整的應用程式：
package com.my.download; 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.io.InputStream; import java.io.OutputStream; import java.io.RandomAccessFile; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import java.nio.channels.FileChannel.MapMode; 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 FileCopy { private final static Path copy_from = Paths.get("C:/rafaelnadal/tournaments/2009/videos/Rafa Best Shots.mp4"); private final static Path copy_to = Paths.get("C:/Rafa Best Shots.mp4"); private static long startTime, elapsedTime; private static int bufferSizeKB = 4;//also tested for 16, 32, 64, 128, 256 and 1024 private static int bufferSize = bufferSizeKB * 1024; public static void main(String[] args) throws Exception { transferfrom(); transferTo(); nonDirectBuffer(); directBuffer(); mapperedBuffer(); ioBufferedStream(); ioUnBufferedStream(); copyPath2Path(); copyInputStream2Path(); copyPath2OutputStream(); //randomReadFile(); } public static void transferfrom() { 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); } public static void transferTo() throws Exception{ 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); } public static void nonDirectBuffer(){ 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(); ByteBuffer bytebuffer = ByteBuffer.allocate(bufferSize); int bytesCount; while ((bytesCount = fileChannel_from.read(bytebuffer)) > 0) { bytebuffer.flip(); fileChannel_to.write(bytebuffer); 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); } public static void directBuffer(){ try ( FileChannel fileChannel_to = FileChannel.open(copy_to, EnumSet.of(StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)); FileChannel fileChannel_from = (FileChannel.open(copy_from, EnumSet.of(StandardOpenOption.READ)));) { startTime = System.nanoTime(); ByteBuffer bytebuffer = ByteBuffer.allocateDirect(bufferSize); int bytesCount; while ((bytesCount = fileChannel_from.read(bytebuffer)) > 0) { bytebuffer.flip(); fileChannel_to.write(bytebuffer); 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); } public static void mapperedBuffer() throws Exception{ 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(); int i=0; long size=fileChannel_from.size()/30; ByteBuffer rr,ww=null; while((i<fileChannel_from.size()) && ((fileChannel_from.size()-i))>size){ rr=fileChannel_from.map(MapMode.READ_ONLY, i, size); ww=fileChannel_to.map(MapMode.READ_WRITE, i, size); ww.put(rr); rr.clear(); ww.clear(); i+=size; } rr=fileChannel_from.map(MapMode.READ_ONLY, i, fileChannel_from.size()-i); ww=fileChannel_to.map(MapMode.READ_WRITE, i, fileChannel_from.size()-i); ww.put(rr); rr.clear(); ww.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); } public static void ioBufferedStream(){ 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); } public static void ioUnBufferedStream(){ File inFileStr = copy_from.toFile(); File outFileStr = copy_to.toFile(); 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); } public static void copyPath2Path(){ 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); } public static void copyInputStream2Path(){ 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); } public static void copyPath2OutputStream(){ 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); } } public static void randomReadFile(){ try( RandomAccessFile read = new RandomAccessFile("C:\\Users\\asus\\Desktop\\cn_windows_7_ultimate_with_sp1_x86_dvd_618763.iso","r"); RandomAccessFile writer = new RandomAccessFile("C:\\Users\\asus\\Desktop\\dwTest\\cn_windows_7_ultimate_with_sp1_x86_dvd_618763.iso","rw");){ startTime = System.nanoTime(); byte[] b = new byte[200*1024*1024]; while(read.read(b)!=-1){ writer.write(b); } elapsedTime = System.nanoTime() - startTime; System.out.println("Elapsed Time is " + (elapsedTime / 1000000000.0) + " seconds"); }catch(Exception e){ System.err.println(e); } deleteCopied(copy_to); } public static void deleteCopied(Path path){ try { Files.deleteIfExists(path); }catch (IOException ex) { System.err.println(ex); } } }
輸出結果排序比較複雜，其中包含了很多資料。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（或執行次數，跳過了前三次執行）。
FileChannel 和非直接模式 Buffer vs. FileChannel 和直接模式 Buffer
從下圖看來，如果快取小於 256KB，那麼非直接模式的 Buffer 快一點，而快取大於 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 執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：
