Java实现文件拷贝

Java实现文件拷贝

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，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，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

123456789 Eclipse(Juno) JVM(Sun JDK1.7) 参数：
-Xms1536m
-Xmx1536m
-Xverify:none -XX:+UseParallelGC
-XX:PermSize=128M
-XX:MaxPermSize=128M
OS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));
    }
}

接下来请看第2页精彩内容：