java - HttpServlet 是否必须响应请求？

Question

我有几个在服务器端执行操作的 servlet。在一些上，我只是编码一些不必要的数据并将其发送回来，这似乎毫无意义。你必须回应吗？当您只说 return 时会发生什么？我以前这样做过，似乎没有什么问题，但我对 servlet 还比较陌生。简单地返回会产生超出我想象的后果吗？当你回来时到底会发生什么？

if(request.getParameter("name").equals("saveusedcards")) {
        String sessId = request.getSession().getId();
        //encode request with confirmation that cards were successfully updated
        if(usersUpdatedCards.get(sessId).isEmpty()){
            //no cards were seen

        }
        boolean success = DataDAO.updateCards(usersUpdatedCards.get(sessId));

        if(success){
            System.out.println("Data base update successfull!");
            String responseMessage = new Gson().toJson("card successfully udpated");
            response.setContentType("application/json");
            response.setCharacterEncoding("UTF-8");
            System.out.println("updated cards response message: "+responseMessage);
            response.getWriter().write(responseMessage);
            return;
        } else {
            System.out.println("Data base update failed...");
            String responseMessage = new Gson().toJson("card was not successfully updated");
            response.setContentType("application/json");
            response.setCharacterEncoding("UTF-8");
            System.out.println("updated cards response message: "+responseMessage);
            response.getWriter().write(responseMessage);
            return;
        }
    } 

Answer 1

Servlet 必须为客户端生成 HTTP 响应，但是在响应正文中不返回任何内容是完全可以接受的。这样做时，您的 servlet 应通过发送响应代码 204(无内容)向客户端明确这一点。引用:https://httpstatuses.com/204

下面是如何通过 doGet 方法设置响应代码的示例。您可以通过 doPost 或 service 方法执行相同的操作。

@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
               throws IOException, ServletException {

    // Do whatever work you need to do here...

    res.setStatus(HttpServletResponse. SC_NO_CONTENT);  // This returns a 204
}