(tomcat/webapps/mymemo/ListServlet.java)

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.sql.*;

public class ListServlet extends HttpServlet {

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

        if (request.getAttribute("message") == null) {
            request.setAttribute("message", "hello paiza memo");
        }

        String url = "jdbc:mysql://localhost/memo";
        String user = "root";
        String password = "";

        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (Exception e) {
            e.printStackTrace();
        }

        String sql = "SELECT * FROM posts";
        try (Connection connection = DriverManager.getConnection(url, user, password);
             PreparedStatement statment = connection.prepareStatement(sql);
             ResultSet results = statment.executeQuery()) {

            ArrayList<HashMap<String, String>> rows = new ArrayList<HashMap<String, String>>();

            while (results.next()) {
                HashMap<String, String> columns = new HashMap<String, String>();

                String id = results.getString("id");
                columns.put("id", id);

                String title = results.getString("title");
                columns.put("title", title);

                String content = results.getString("content");
                columns.put("content", content);

                rows.add(columns);
            }

            request.setAttribute("rows", rows);

        } catch (Exception e) {
            request.setAttribute("message", "Exception:" + e.getMessage());
        }
        String view = "/WEB-INF/views/list.jsp";
        RequestDispatcher dispatcher = request.getRequestDispatcher(view);
        dispatcher.forward(request, response);

    }
}

- Javaの道＞Servlet・JSP
https://www.javaroad.jp/servletjsp/index.html

- Servletアプリ開発：目次 - Web系開発メモ
http://web-dev.hatenablog.com/entry/java/servlet/dev-restful-app/table-of-contents