如果从数据库中检索到的用户名和密码不正确，那么我想在jsp页面本身显示错误，而不是重新定向到另一个页面。
如果用户名和密码无效，现在我正在显示来自验证servlet的消息。如何使用javascript或任何其他工具在前端向jsp视图显示消息？
以下是我的登录表单：
<form id="loginform" class="form-horizontal" name="myForm" method="POST" action="ValidateLoginServlet2.do" onSubmit="return validateLogin()">
<input type="text" class="form-control" name="uname" placeholder="username">
<input id="login-password" type="password" class="form-control" name="pwd" placeholder="password">
<input type="submit" value="Login" href="#" class="btn btn-success" />
</form>
和我的验证登录servlet：
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// processRequest(request, response);
PrintWriter out = response.getWriter();
String username = request.getParameter("uname");
String password = request.getParameter("pwd");
System.out.println(username);
System.out.println(password);
try
{
Connection con = OracleDBConnection.getConnection();
PreparedStatement statement = con.prepareStatement("select firstname, password from registration where firstname =? and password=?");
statement.setString(1, username);
statement.setString(2, password);
ResultSet result = statement.executeQuery();
if(result.next()){
response.sendRedirect("LoginSuccessful.jsp");
}else{
out.println("username and password are incorrect");
}
}catch(Exception e){
System.out.println("DB related Error");
e.printStackTrace();
}
}
您可以使用
<form id="loginform" class="form-horizontal" name="myForm" method="POST" action="ValidateLoginServlet2.do" onSubmit="return validateLogin()">
<input type="text" class="form-control" name="uname" placeholder="username">
<input id="login-password" type="password" class="form-control" name="pwd" placeholder="password">
<input type="submit" value="Login" href="#" class="btn btn-success" />
<span style="color:red;">${errMsg}</span>
</form>
在您的servlet中，您在else语句中设置了一条错误消息，如下所示：
if(result.next()) {
response.sendRedirect("LoginSuccessful.jsp");
}else{
request.setAttribute("errMsg", "username and password are incorrect");
// The following will keep you in the login page
RequestDispatcher rd = request.getRequestDispatcher("/login.jsp");
rd.forward(request, response);
}
为了防止在登录成功的if块中的下一次登录时显示相同的错误，您可以像这样重置ErrMsg：
request.setAttribute("errMsg", "");
在您的else部分验证登录servlet放置以下代码：
if(result.next()){
response.sendRedirect("LoginSuccessful.jsp");
}
else{
HttpSession session = request.getSession();
session.setAttribute("wrong_uname_pass", "1");
response.sendRedirect("index.jsp");
}
并将以下代码放在index. jsp的第一部分（或您的登录表单在哪里）
<%
if(session.getAttribute("wrong_uname_pass") != null){
%>
<script>
alert("wrong user name or password");
</script>
<%
session.removeAttribute("wrong_uname_pass");
}
%>
