如何在HTTP响应中设置标头？

Question

我有一个servlet A,我在HTTP响应中设置一个标头:

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);
}

现在在servlet B中,我试图获取在servlet A中设置的头值:

public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    String userid = request.getHeader("REMOTE_USER");
}

但是这里userid的价值即将到来null.请让我知道我在这里缺少什么.

Answer 1

首先,你必须了解其本质

response.sendRedirect(newUrl);

它通过URL给客户端(浏览器)302 http代码响应.然后,浏览器在该URL上发出单独的GET请求.并且该请求在第一个请求中不知道标题.

因此,如果需要将标头从Servlet A传递到Servlet B,sendRedirect将不起作用.

如果您希望此代码有效 - 请在Servlet A中使用RequestDispatcher(而不是sendRedirect).此外,使用相对路径总是更好.

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");
}