import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import feed.data.Post;

public class FeedServlet extends HttpServlet {

	/**
	 * All of the posts, ordered by time. Old messages at the
	 * beginning, new messages at the end.
	 */
	private List<Post> postsByTime = new ArrayList<>();

	/**
	 * Map of user names to posts made by that user.
	 */
	private Map<String, List<Post>> postsByUser = new HashMap<>();

	@Override
	public void init(){

		long now = System.currentTimeMillis();
		// for fake data, add an offset so posts aren't all at the same time
		long offset = 15*60*1000;

		// add a bunch of fake data for testing
		addPost("Ada", "Hello world!", now+offset);
		addPost("Grace", "I've always been more interested in the future than in the past.", now+offset*2);
		addPost("Stanley", "Meow", now+offset*3);
		addPost("Stanley", "Purr", now+offset*4);
		addPost("Grace", "From then on, when anything went wrong with a computer, we said it had bugs in it.", now+offset*5);
		addPost("Ada", "Mathematical Science shows what is. It is the language of the unseen relations between things.", now+offset*6);
		addPost("Grace", "Please cut off a nanosecond and send it over to me.", now+offset*7);
		addPost("Stanley", "Growl!", now+offset*8);
	}

	/**
	 * Adds a post to the postsByTime and postsByUser data structures.
	 */
	private void addPost(String user, String message, long time){
		Post post = new Post(user, message, new Date(time));
		postsByTime.add(post);

		if(!postsByUser.containsKey(user)){
			postsByUser.put(user, new ArrayList<>());
		}
		postsByUser.get(user).add(post);
	}

	@Override
	public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
		String requestUrl = request.getRequestURI();
		String user = requestUrl.substring("/feed/".length());

		if("".equals(user)){
			request.setAttribute("title", "All Posts");
			request.setAttribute("posts", postsByTime);
		}
		else{
			request.setAttribute("title", "Posts by " + user);

			if(postsByUser.containsKey(user)){
				request.setAttribute("posts", postsByUser.get(user));
			}
		}

		request.getRequestDispatcher("/WEB-INF/jsp/feed.jsp").forward(request,response);
	}
}

package feed.data;

import java.util.Date;

public class Post {
	private String user;
	private String message;
	private Date date;

	public Post(String user, String message, Date date) {
		this.user = user;
		this.message = message;
		this.date = date;
	}

	public String getUser() {
		return user;
	}

	public void setUser(String user) {
		this.user = user;
	}

	public String getMessage() {
		return message;
	}

	public void setMessage(String message) {
		this.message = message;
	}

	public Date getDate() {
		return date;
	}

	public void setDate(Date date) {
		this.date = date;
	}

}