在Java NIO中，如果两个通道中有一个是FileChannel，那你可以直接将数据从一个channel传输到另外一个channel。
RandomAccessFile fromFile =newRandomAccessFile("fromFile.txt","rw");
FileChannel fromChannel = fromFile.getChannel();
RandomAccessFile toFile =newRandomAccessFile("toFile.txt","rw");
FileChannel toChannel = toFile.getChannel();
longposition =0;
longcount = fromChannel.size();
toChannel.transferFrom(position, count, fromChannel);
方法的输入参数position表示从position处开始向目标文件写入数据，count表示最多传输的字节数。如果源通道的剩余空间小于 count 个字节，则所传输的字节数要小于请求的字节数。
RandomAccessFile fromFile =newRandomAccessFile("fromFile.txt","rw");
FileChannel fromChannel = fromFile.getChannel();
RandomAccessFile toFile =newRandomAccessFile("toFile.txt","rw");
FileChannel toChannel = toFile.getChannel();
long position =0;
long count = fromChannel.size();
fromChannel.transferTo(position, count, toChannel);
transferTo()方法将数据从FileChannel传输到其他的channel中
