经过一组简单的测试发现JAVA NIO提供的文件内存映射方法实现文件拷贝速度最快，不管是大文件还是小文件，特别是大文件的拷贝速度比普通方法提高20倍，唯一有个前提就是内存需要足够大，否则文件映射肯定失败（当然可以通过分割文件，部分映射的方法避免，但就比较麻烦了）；其次NIO提供的文件管道传输速度也比较好，如果没法做文件内存映射，推荐这种拷贝方法；另外，Buffer的大小，对于读写速度还是有影响的，香港虚拟主机，基本就是Buffer越大读写越快（有个疑问就是Buffer.allocateDirec()效率提高不明显）；最后，总体看来NIO的效率比老IO高，不管使用哪种方式，老IO使用流读写只能一个字节一个字节的抠，香港空间，NIO使用块的方式读写还是相对比较快，所以没有特别需求的情况下，推荐使用NIO，目前NIO基本能覆盖老IO的所有功能（当然NIO还提供N多新功能）。
测试环境
Eclipse(Juno) JVM(Sun JDK1.7) 参数：-Xms1536m-Xmx1536m-Xverify:none -XX:+UseParallelGC-XX:PermSize=128M-XX:MaxPermSize=128MOS参数：Win7 64Bit + 4GB物理磁盘空间充足
测试代码
import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.RandomAccessFile;import java.nio.ByteBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;public class FileCopy {private static final int BUFFER_SIZE_1024 = 1024;private static final int BUFFER_SIZE_4096 = 4096;private static final int BUFFER_SIZE_10240 = 10240;private static final String FROM_FILE_42MB = “G:/from_42MB.rar”;private static final String FROM_FILE_1GB = “G:/from_350MB.rar”;private static int BUFFER_SIZE = BUFFER_SIZE_1024;private static String FROM_FILE = FROM_FILE_42MB;/*** @param args* @throws Exception*/public static void main(String[] args) throws Exception {System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();BUFFER_SIZE = BUFFER_SIZE_4096;System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();BUFFER_SIZE = BUFFER_SIZE_10240;System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();BUFFER_SIZE = BUFFER_SIZE_1024;FROM_FILE = FROM_FILE_1GB;System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();BUFFER_SIZE = BUFFER_SIZE_4096;FROM_FILE = FROM_FILE_1GB;System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();BUFFER_SIZE = BUFFER_SIZE_10240;FROM_FILE = FROM_FILE_1GB;System.out.println(“File :” + FROM_FILE + ” —- Buffer Size : ” + BUFFER_SIZE + “————–“);testFileCopy();}private static void testFileCopy() throws FileNotFoundException,IOException {coypByMbb();copyByNioTransferFrom();copyByNioTransferTo();coypByBufferRead();coypByFastBufferRead();coypByStream();//Old IO style}/*** 使用FileChannel.transferFrom()实现* @throws FileNotFoundException* @throws IOException*/private static void copyByNioTransferFrom() throws FileNotFoundException,IOException {long startTime = System.currentTimeMillis();RandomAccessFile fromFile = new RandomAccessFile(FROM_FILE, “rw”);FileChannel fromChannel = fromFile.getChannel();RandomAccessFile toFile = new RandomAccessFile(“G:/to1.rar”, “rw”);FileChannel toChannel = toFile.getChannel();long position = 0;long count = fromChannel.size();toChannel.transferFrom(fromChannel, position, count);long endTime = System.currentTimeMillis();System.out.println(“copyByNioTransferFrom time consumed(buffer size no effect) : “+ (endTime – startTime));}/*** 使用FileChannel.transferTo()实现* @throws FileNotFoundException* @throws IOException*/private static void copyByNioTransferTo() throws FileNotFoundException,IOException {long startTime = System.currentTimeMillis();RandomAccessFile fromFile = new RandomAccessFile(FROM_FILE, “rw”);FileChannel fromChannel = fromFile.getChannel();RandomAccessFile toFile = new RandomAccessFile(“G:/to2.rar”, “rw”);FileChannel toChannel = toFile.getChannel();long position = 0;long count = fromChannel.size();fromChannel.transferTo(position, count, toChannel);long endTime = System.currentTimeMillis();System.out.println(“copyByNioTransferTo time consumed(buffer size no effect) : “+ (endTime – startTime));}/*** 使用Channel, Buffer简单读写实现* @throws IOException*/private static void coypByBufferRead() throws IOException {long startTime = System.currentTimeMillis();FileInputStream fin = new FileInputStream(FROM_FILE);FileOutputStream fout = new FileOutputStream(“G:/to3.rar”);FileChannel fcin = fin.getChannel();FileChannel fcout = fout.getChannel();ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);while (true) {buffer.clear();int r = fcin.read(buffer);if (r == -1) {break;}buffer.flip();fcout.write(buffer);}long endTime = System.currentTimeMillis();System.out.println(“coypByBufferRead time consumed(buffer size take effect) : “+ (endTime – startTime));}/*** 使用连续内存的Buffer实现* @throws IOException*/private static void coypByFastBufferRead() throws IOException {long startTime = System.currentTimeMillis();FileInputStream fin = new FileInputStream(FROM_FILE);FileOutputStream fout = new FileOutputStream(“G:/to4.rar”);FileChannel fcin = fin.getChannel();FileChannel fcout = fout.getChannel();ByteBuffer buffer = ByteBuffer.allocateDirect(BUFFER_SIZE);while (true) {buffer.clear();int r = fcin.read(buffer);if (r == -1) {break;}buffer.flip();fcout.write(buffer);}long endTime = System.currentTimeMillis();System.out.println(“coypByFastBufferRead time consumed(buffer size take effect) : “+ (endTime – startTime));}/*** 使用文件内存映射实现* @throws IOException*/private static void coypByMbb() throws IOException {long startTime = System.currentTimeMillis();FileInputStream fin = new FileInputStream(FROM_FILE);RandomAccessFile fout = new RandomAccessFile(“G:/to5.rar”, “rw”);FileChannel fcin = fin.getChannel();FileChannel fcout = fout.getChannel();MappedByteBuffer mbbi = fcin.map(FileChannel.MapMode.READ_ONLY, 0,fcin.size());MappedByteBuffer mbbo = fcout.map(FileChannel.MapMode.READ_WRITE, 0,fcin.size());mbbo.put(mbbi);mbbi.clear();mbbo.clear();long endTime = System.currentTimeMillis();System.out.println(“coypByMbb time consumed(buffer size no effect) : ” + (endTime – startTime));}/*** 使用传统IO的流读写方式实现* @throws IOException*/private static void coypByStream() throws IOException {long startTime = System.currentTimeMillis();FileInputStream fin = new FileInputStream(FROM_FILE);FileOutputStream fout = new FileOutputStream(“G:/to6.rar”);byte[] buffer = new byte[BUFFER_SIZE];while (true) {int ins = fin.read(buffer);if (ins == -1) {fin.close();fout.flush();fout.close();break;} else{fout.write(buffer, 0, ins);}}long endTime = System.currentTimeMillis();System.out.println(“coypByStream time consumed(buffer size take effect) : ” + (endTime – startTime));}}也就越容易失败，还不如怀揣一颗平常心，
