java.io.StreamCorruptedException: invalid type code: AC

     private Server_Student Loginresult(String numberString ,String passworString) {
        // TODO Auto-generated method stub
         if (!isConnected) {
            for (int i = 0; i < 10; i++) {
                getsocket();
            }
        }
         
         Student student = new Student(numberString, passworString);
        Client_Student client_Student = new Client_Student(student);
        Server_Student server_Student = null;
        try {
            oos.writeObject(client_Student);
            server_Student = (Server_Student) ois.readObject();
        } catch (IOException | ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("Loginresult出错了");
        }
        System.out.println(server_Student);
        return server_Student;
    }

server_Student = (Server_Student) ois.readObject(); 这里一直出现错误,但是不明白哪里错了.求解