>每当我单击submit它都会重定向到空白页面，但网址工作正常 我对我的响应标签是否错误感到困惑
法典：
protected void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException {
Connection con=connector.getConnection();
String username = request.getParameter("username");
String password = request.getParameter("password");
String message = null;
String url = null;
try {
PreparedStatement ps = con.prepareStatement( "Select * from data Where username=?'" + username + "' and password=?'" + password + "';");
ps.setString(1, request.getParameter("username"));
ps.setString(2, request.getParameter("password"));
ResultSet rs = ps.executeQuery();
if(rs.next()) {
RequestDispatcher rd=request.getRequestDispatcher("practice1.jsp");
rd.forward(request,response);
}
else {
message="Invalid Input Please Try Again";
request.setAttribute("message", message);
request.setAttribute("url", url);
}
}
catch(SQLException ex){
message="ERROR"+ex.getMessage();
ex.printStackTrace();
}
请让我知道我错过了什么。
尝试通过更改以下代码来修复它：
以前：
PreparedStatement ps = con.prepareStatement( "Select * from data Where username=?'" + username + "' and password=?'" + password + "';");
ps.setString(1, request.getParameter("username"));
ps.setString(2, request.getParameter("password"));
后：
PreparedStatement ps = con.prepareStatement( "Select * from data Where username=? and password=?");
ps.setString(1, username);
ps.setString(2, password);
在 if 块中，只要有数据，请求调度员就会将请求转发到 practice1.jsp 页面。
if(rs.next()) {
RequestDispatcher rd=request.getRequestDispatcher("practice1.jsp");
rd.forward(request,response);
}
但是在 else 阻止的情况下，仅请求设置如下：
request.setAttribute("message", message);
request.setAttribute("url", url);
但是，如果我们想在 UI 中显示，我们应该指定响应而不是请求。
else {
message="Invalid Input Please Try Again";
response.getWriter().print("<html><head><title>
Oops an error happened!</title> </head>");
response.getWriter().print("<body>"+message+"</body>");
response.getWriter().println("</html>");
//request.setAttribute("message", message);
//request.setAttribute("url", url);
}