提交响应后无法转发 - Servlet

Question

我正在尝试从 HTTPSession 注销并将用户重定向到登录页面。

下面是我完整的 Http servlet 代码。

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LogoutServlet extends HttpServlet {

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
{
    super.doGet(req, resp);
    processRequest(req, resp);
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
{
    super.doPost(req, resp);
    processRequest(req, resp);
}

private void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
    final HttpSession session = request.getSession(false);
    if (session != null) 
    {
        session.invalidate();
    }

    response.sendRedirect("/login.html");
    //getServletContext().getRequestDispatcher("/login.html").forward(request, response);
}

}

但得到以下异常：

java.lang.IllegalStateException: Cannot forward after response has been committed
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:339)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
at com.controller.LogoutServlet.processRequest(LogoutServlet.java:41)

Answer 1

删除调用

super.doGet(req, resp); // and
super.doPost(req, resp);

基类实现只是尝试抛出不支持 GET 或 POST 的错误消息。

// HttpServlet#doGet() calls
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);

以上行是已经提交响应的内容。

Answer 2

你为什么不重定向而不是转发？

    response.sendRedirect("/login.html");