UTF-8转GDK

package zuoye;

//2017.0321 by小方
import java.io.*;

public class F0321 {
    public static void main(String args[]) throws Exception{
        String a= "d:\\my.txt";
        FileInputStream f = new FileInputStream(a);
        InputStreamReader i = new InputStreamReader(f,"UTF-8");
        BufferedReader br = new BufferedReader(i);
        String s = br.readLine();
        if(s==null){
            System.out.println(a);
            return;
        }else{
            System.out.println(s);
        }
        FileOutputStream fo = new FileOutputStream("d:\\my2.txt");
        OutputStreamWriter b = new OutputStreamWriter(fo,"GBK");
        b.write(s.substring(0));
        b.flush();
    }

}