java.lang.IllegalStateException：在Servlet中提交响应后无法转发[重复]

未提供登录名和/或密码时，您不会在前进后返回。入门者之间普遍存在误解，即该

forward()

您需要添加一个

return;

if ((login==null)|(password==null)){    RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp");    requestDispatcher.forward(request, response);    return;}

或添加一个

else

if ((login==null)|(password==null)){    RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp");    requestDispatcher.forward(request, response);} else {    // Now we think that we are successfully logged in.    // Yes, that above comment is now finally true.    // Put your bunch of non-DRY if-else pre here.}