如何使用servlet映射显示在线用户

Question

i want to show online users using this servlet ......

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;


import javax.servlet.ServletContext;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.chatapp.useroperation.Client;

@WebServlet(name = "onlineUsersServlet", urlPatterns = { "/getOnlineUsersList" })
public class ListOfOnlineUsers extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {

        String commaSepeparatedStr ="";
        ServletContext appScope = request.getServletContext();
        String channel = request.getParameter("channel");
        final Map<String, List<Client>> clients = (Map<String, List<Client>>) appScope.getAttribute(LoginServlet.CLIENTS);
        System.out.println(clients);
        if(clients.size()> 0){
            final List<Client> onlineClients = clients.get(channel);
            if(onlineClients !=null){
                for (Client client : onlineClients) {
                    if(commaSepeparatedStr.equals("") ){
                        commaSepeparatedStr = client.getUserName();
                    }else{
                        commaSepeparatedStr =commaSepeparatedStr+","+ client.getUserName();

                    }
                }
            }
        }
        response.getWriter().write(commaSepeparatedStr);
        response.flushBuffer(); 

    }

}

how can i pass value to this servlet from a jsp so that it store the username in its list......is it possible to put value in that servlet from session.

Answer 1

If you want to Store a Value from a session to a servlet, just attach an attribute to the Session;

During Login, get the username and store the value into the Session;

HttpSession sess = request.getSession();//Create new Session
//Get the username from login input
String username = request.getParameter("name");

//Attach the name to the Session.

sess.setAttribute("username", username);

Get the value anytime as long as the session is active.

HttpSession sess = request.getSession(false);//Use the current Session
//Get the value fron the Session 
String username = (String) sess.getAttribute("username");//get the Attribute Username

You need to have Attached the Attribute to the Session before you can get it this way.

Answer 2

in your jsp do something like this:

<form action="/YOURWEBAPPNAME/onlineUsersServlet/getOnlineUsersList" method="get">
    <input type="text" name="test" value="Hello World">
    <input type="submit" value="Send">
</form>

in you doGet method do this:

String userInput = request.getParameter("test");

and feel free using that stuff.

put that stuff in the session with:

request.getSession(false).setAttribute("input",userInput);

and read it with:

 String lInput = (String) request.getSession(false).getAttribute("input");

Answer 3

There are variables with a different scope that you can, or not, access from different places in your code. In JavaEE there are variables with request, session and application scope.

The request scope means that you can set it and use it in all your classes for the current request and that's what you seem to need right now.

I'm sorry I can't help you more right now but with this info Google or the SO search box should be your friend. I'll add details later.

Edit -

Stefan beike's answer has these details I'm talking about.