Java 如何在 HTTP 响应中设置标头？
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How to set a header in an HTTP response?
提问by Pakira
I've a servlet Awhere I'm setting a header in the HTTP response:
我有一个 servlet A，我在 HTTP 响应中设置了一个标头：
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String userName=request.getParameter("userName");
String newUrl = "http://somehost:port/ServletB";
response.addHeader("REMOTE_USER", userName);
response.sendRedirect(newUrl);
}
Now in a servlet B, I'm trying to get the header value that was set in the servlet A:
现在在 servlet B 中，我试图获取在 servlet A 中设置的标头值：
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String userid = request.getHeader("REMOTE_USER");
}
But here the value of useridis coming as null. Please let me know what I'm missing here.
但是这里userid的值是null. 请让我知道我在这里缺少什么。
采纳答案by pubsy
First of all you have to understand the nature of
首先你要了解它的本质
response.sendRedirect(newUrl);
It is giving the client (browser) 302 http code response with an URL. The browser then makes a separate GET request on that URL. And that request has no knowledge of headers in the first one.
它向客户端（浏览器）提供带有 URL 的 302 http 代码响应。然后浏览器对该 URL 发出单独的 GET 请求。并且该请求不知道第一个中的标头。
So sendRedirect won't work if you need to pass a header from Servlet A to Servlet B.
因此，如果您需要将标头从 Servlet A 传递到 Servlet B，则 sendRedirect 将不起作用。
If you want this code to work - use RequestDispatcher in Servlet A (instead of sendRedirect). Also, it is always better to use relative path.
如果您希望此代码工作 - 在 Servlet A 中使用 RequestDispatcher（而不是 sendRedirect）。此外，最好使用相对路径。
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
String userName=request.getParameter("userName");
String newUrl = "ServletB";
response.addHeader("REMOTE_USER", userName);
RequestDispatcher view = request.getRequestDispatcher(newUrl);
view.forward(request, response);
}
========================
========================
public void doPost(HttpServletRequest request, HttpServletResponse response)
{
String sss = response.getHeader("REMOTE_USER");
}
回答by mgorniew
Header fields are not copied to subsequent requests. You should use either cookie for this (addCookie method) or store "REMOTE_USER" in session (which you can obtain with getSession method).
标头字段不会复制到后续请求中。您应该为此使用 cookie（addCookie 方法）或在会话中存储“REMOTE_USER”（您可以使用 getSession 方法获取）。
回答by hd1
In my Controller, I merely added an HttpServletResponse parameter and manually added the headers, no filter or intercept required and it works fine:
在我的控制器中，我只添加了一个 HttpServletResponse 参数并手动添加了标头，不需要过滤器或拦截，它工作正常：
httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
httpServletResponse.setHeader("Access-Control-Allow-Methods", "GET, OPTIONS");
httpServletResponse.setHeader("Access-Control-Allow-Headers","Origin, X-Requested-With, Content-Type, Accept, X-Auth-Token, X-Csrf-Token, WWW-Authenticate, Authorization");
httpServletResponse.setHeader("Access-Control-Allow-Credentials", "false");
httpServletResponse.setHeader("Access-Control-Max-Age", "3600");
