import static java.nio.file.StandardOpenOption.*;

import java.nio.file.*;

import java.nio.channels.*;

import java.io.IOException;

import java.util.EnumSet;

public class FileBackup {

/**

* @param args

*/

public static void main(String[] args) {

// TODO 自动生成方法存根

Path file = Paths.get(System.getProperty("user.home")).resolve(

"Beginning Java Stuff").resolve("Sayings.txt");

if (!Files.exists(file)) {

System.err.println(file + " is not exist.");

System.exit(1);

}

file.toAbsolutePath();//将路径转化为绝对路径，如果已经是绝对路径则原样返回

Path tofile= createBackupFilePath(file);//创建复制文件路径

try{

FileChannel inCh=(FileChannel)(Files.newByteChannel(file));//filechannel具有更高的功能

WritableByteChannel outCh=Files.newByteChannel(tofile,EnumSet.of(WRITE,CREATE));//新建写入文件通道

int byteWritten=0;

long byteCount=inCh.size();

while(byteWritten

byteWritten+=inCh.transferTo(byteWritten,byteCount-byteWritten,outCh);

//Transfers bytes from this channel's file to the given writable byte channel.

//long transferTo(long position,long count,WritableByteChannel target) position是开始位置，count是要读取的字节数，target是目标通道

//返回的是实际转化的字节数

}

System.out.printf("File copy complete. %d bytes copied to %s%n", byteCount, tofile);

}catch(IOException e){

e.printStackTrace();

}

}

public static Path createBackupFilePath(Path file){

Path parent=file.getParent();

String name=file.getFileName().toString();//getFilename返回文件名(路径类型)，也就是路径中距离根目录最远的

int period=name.indexOf('.');

if(period==-1){

period=name.length();

}

String nameAdd="_backup";

Path backup=parent.resolve(name.substring(0,period)+nameAdd+name.substring(period));//修改路径，建立复制文件路径

while(Files.exists(backup)){//检测新建的路径是否存在，如果存在则继续在文件名后面加_backup

name=backup.getFileName().toString();

backup=parent.resolve(name.substring(0,period)+nameAdd+name.substring(period));

period+=nameAdd.length();

}

return backup;

}

}