java高效实现大文件拷贝功能

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
 
public class BigFileCopy {
 
 
 /**
 * 通过channel到channel直接传输
 * @param source
 * @param dest
 * @throws IOException
 */
 public static void copyByChannelToChannel(String source, String dest) throws IOException {
 File source_tmp_file = new File(source);
 if (!source_tmp_file.exists()) {
 return ;
 }
 RandomAccessFile source_file = new RandomAccessFile(source_tmp_file, "r");
 FileChannel source_channel = source_file.getChannel();
 File dest_tmp_file = new File(dest);
 if (!dest_tmp_file.isFile()) {
 if (!dest_tmp_file.createNewFile()) {
 source_channel.close();
 source_file.close();
 return;
 }
 }
 RandomAccessFile dest_file = new RandomAccessFile(dest_tmp_file, "rw");
 FileChannel dest_channel = dest_file.getChannel();
 long left_size = source_channel.size();
 long position = 0;
 while (left_size > 0) {
 long write_size = source_channel.transferTo(position, left_size, dest_channel);
 position += write_size;
 left_size -= write_size;
 }
 source_channel.close();
 source_file.close();
 dest_channel.close();
 dest_file.close();
 }
 
 
 public static void main(String[] args) {
 try {
 long start_time = System.currentTimeMillis();
 BigFileCopy.copyByChannelToChannel("source_file", "dest_file");
 long end_time = System.currentTimeMillis();
 System.out.println("copy time = " + (end_time - start_time));
 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 
}