客户端:ObjectOutputStream在前;ObjectInputStream在后;
            即:先写后读;
服务器端:ObjectInputStream在前;ObjectOutputStream在后;
            即:先读后写;

clinet:
     Socket s = new Socket(InetAddress.getLocalHost(),5000);
    ObjectOutputStream out= new ObjectOutputStream(s.getOutputStream);
    ObjectInputStream in = new ObjectInputStream(s.getInputStream);

server:
    ServerSocket socket = new ServerSocket(5000);
    Socket s = socket.accept();
    ObjectInputStream in = new ObjectInputStream(s.getInputStream);
    ObjectOutputStream out = new ObjectOutputStream(s.getOutputStream);