java 服务端与用户端连接问题

用户端：
InputStream is = client.getInputStream();
InputStreamReader isr=new InputStreamReader(is);
BufferedReader br=new BufferedReader(isr);//输入
OutputStream os = client.getOutputStream();
PrintWriter print=new PrintWriter(os);//输出

    System.out.println(br.readLine());//输入：L登录；R注册；Q退出程序
    print.write(s.next());//用户输入选择后发给服务端
    print.close();
    System.out.println(br.readLine());//请输入用户名
    print.write(s.next());//用户名发给服务端
    print.close();
    System.out.println(br.readLine());//请输入密码
    print.write(s.next());//密码发给服务端
    print.close();

服务端
InputStream is = client.getInputStream();
InputStreamReader isr=new InputStreamReader(is);
BufferedReader br=new BufferedReader(isr);//输入
OutputStream os = client.getOutputStream();
PrintWriter print=new PrintWriter(os);//输出

    System.out.println("开始交互");
    print.write("输入：L登录；R注册；Q退出程序");
    print.close();

    String cho = br.readLine();
    System.out.println(cho);
    switch(cho) {
        case "L":
            print.write("请输入用户名：");
            print.close();
            String userName = br.readLine();
            print.write("请输入密码：");
            print.close();
            String password = br.readLine();
            break;

提示后，输入L后显示null，然后阻塞

萌新求解问题出在哪里了