帮忙看下这个java套接字编程：

import java.io.*;
import java.net.*;public class Client {    /**
     * @param args the command line arguments
     */
    public static void main(String argv[]) throws Exception {
        String path = new String("C:\\Users\\Lin\\Desktop\\test.tny");
        String buf = null;
        String res = null;
        FileReader fr = new FileReader(path);
        BufferedReader br = new BufferedReader(fr);
        Socket ClientSocket = new Socket("Lin-PC", 6789);
        DataOutputStream outToServer = new DataOutputStream(ClientSocket.getOutputStream());
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(ClientSocket.getInputStream()));
        while ((buf = br.readLine()) != null) {
//        System.out.print(buf+"\n");
            outToServer.writeBytes(buf + '\n');
        };
        br.close();
        fr.close();
//        res=inFromServer.readLine();
//        System.out.print(res);
        outToServer.close();
    }
}import java.io.*;
import java.net.*;public class Server {    /**
     * @param args the command line arguments
     */
    public static void main(String argv[]) throws Exception {
        String path = new String("C:\\Users\\Lin\\Desktop\\res.txt");
        FileWriter fw = new FileWriter(path);
        BufferedWriter bw = new BufferedWriter(fw);
        String sentence = null;
        ServerSocket welcomeSocket = new ServerSocket(6789);
        while (true) {      //循环等待
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            while ((sentence = inFromClient.readLine()) != null) {
                bw.write(sentence);
                bw.newLine();
                bw.flush();
//            System.out.print(sentence+"\n");
            };
//            outToClient.writeBytes("Success!" + "\n");
            fw.close();
            bw.close();
        }
    }
};注释中的从服务器写字符串入套接字传回客户端无法实现，求原因～