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;
}
}