将类的ArrayList从jsp传递到servlet

Question

I have an ArrayList of a class Room. I need to send it from a jsp to a servlet.

It seems the only way an html or a jsp can send values to a servlet is via a form, the method I tried was to pass it as a hidden parameter as follows:

<input type="hidden" name="allRooms" value="<%=request.getAttribute("allRooms") %>" />

But in the servlet to which i submit this form I get a compile error "String cannot be converted to List" for the following:

 List<Room> allRooms=(List<Room>)request.getParameter("allRooms");

Just converting the parameter to an Object type first and then converting it to a List as shown below gives the same exception but this time as a Runtime Exception:

 Object a=(Object)request.getParameter("allRooms");
 List<Room> allRooms=(List<Room>)a;

Is there any method to pass the List to the servlet or I will have to set it as a session variable in the JSP ?

Thanks in advance.

Answer 1

Is there any method to pass the List to the servlet or I will have to set it as a session variable in the JSP ?

Use session .That is one best solution.

There is no way to represent an ArrayList in HTML to send via html form. Use session instead.

Answer 2

I think if you pass the following params, and array is formed in servlet side

param[0]=ss , param[1]=ssw

You could do this.

List<String> roomParams =(List<String>)request.getParameter("param");

But to make this.

List<Room> allRooms=(List<Room>)request.getParameter("allRooms");

That I think is not possible, so you should use Session attributes

session.setAttribute("allRooms", new ArrayList<Room>());

Answer 3

I believe you should not be sending the List to Servlet directly and should look out for other options.

How are you generating the ArrayList on the browser page? If it is generated from a multi-select element from UI, then you can access the request parameter values as Array in Servlet .

Shishir