如何使用Servlet显示确认消息

Question

I want to add customers to a database using JSPs, JQuery and Servlets. When a customer already exists within the database table I want to show a confirmation message (Customer already exists. Are your sure you want to add the same customer?). When Customer does not exist all the data is written into the table and there is no need to show a confirm message.

My jquery code so far:

$('#myForm').submit(function() {

      var c = confirm("Customer have already. Are your sure you want to add the same customer?");
      return c;

});

And my servlet:

   int i = 0;
   ArrayList<Customer> cus = CustomerDao.addcustomer("abc");
   i = cus.size();
   if(i > 0){
        statement;
    }else{
        statement ;
    }

When I click the submit button it always shows the confirmation message. I don't wanna show confirmation message when the customer does not already exist in the database.

Answer 1

您可以在提交时向客户端写一个cookie，然后检查该cookie是否在那里，如果不进行正常处理，则显示消息。

Answer 2

Assuming that you have a jsp like login.jsp which posts to servlet eg myservlet which in turn calls a method to query to database. I would try the below :-

1. Post the user provided values to the servlet myservlet (post method). Now use these values on a method which queries the database and finds whether this user already exists.

2.If yes , then use RequestDispatcher to the login.jsp . This time give a message that the user already exists. The user needs to fill the info again with new username post the values again.

3. If the user doesn't exists , continue the normal flow and create the user.

Answer 3

1)If you are using ajax for submitting your form data you can write responses and the same will be displayed, eg:-

//in servlet
if(userExists)//dummycode
 response.getWriter().println("User already exists");
 //above will get displayed on your html/jsp page
else
 //logic

2) if you are not using ajax, you can write your response in servlet in an attribute and print the response from that attribute in jsp, eg:-

//in servlet
request.setAttribute("Response","User already exists");
RequestDispatcher rd;
        rd = request.getRequestDispatcher("YourJSPpage");
        rd.forward(request, response);

and in jsp

<%
String msg=request.getAttribute("Response");
%>
if(msg!=null){
<p><%=msg%></p>
}

But as scriptlets in jsp are discouraged you can use JSTL tags eg:-

${requestScope.Response}