Hosting Java Servlet on Apache Tomcat

The servlet uses JDBC. To make the servlet work, put the jar file with the driver in the folder WEB-INF/lib/.
When running the servlet, the driver is not picked up. What am I doing wrong?

UPD: The problem was solved by explicitly creating a driver object Class.forName("com.mysql.jdbc.Driver"). I wonder why this was required here. In a normal Java SE application, it worked even without explicit creation.

Project structure

Java Servlet:

package com.company.app.logic;

import java.sql.ResultSet;
import java.sql.SQLException;

public class Item {

    private int itemId;
    private String itemName;

    public Item(ResultSet rs) {
        try {
            this.itemId = rs.getInt(1);
            this.itemName = rs.getString(2);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public String getItemName() {
        return itemName;
    }

    public int getItemId() {
        return itemId;
    }

    public String toString() {
        return itemName;
    }
}


package com.company.app.logic;
import java.sql.*;
import java.util.*;
public class Main {
    private static Main instance = new Main();
    private static Connection connection;
    private Main() {
       try {
           Class.forName("com.mysql.jdbc.Driver");

           String url = "jdbc:mysql://localhost:3306/maindb";
           connection = DriverManager.getConnection(url, "root", "root");
       } catch (Exception e) {
           e.printStackTrace();
       }
    }
    public static Main getInstance() {
        return instance;
    }
    public List<Item> getItems() {
        List<Item> items = new ArrayList<>();
        Statement statement = null;
        ResultSet rs = null;
        try {
            statement = connection.createStatement();
            rs = statement.executeQuery("SELECT * FROM items");
            while (rs.next()) {
                Item g = new Item(rs);
                items.add(g);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (statement != null) {
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return items;
    }
}


package com.company.app.web;

import com.company.app.logic.Item;
import com.company.app.logic.Main;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

@WebServlet("/items")
public class MainServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");

        PrintWriter pw = resp.getWriter();
        pw.println("<table border=1>");
        try {
            List<Item> l = Main.getInstance().getItems();
            for (Item item : l) {
                pw.println("<tr>");
                pw.println("<td>" + item.getItemId() + "</td>");
                pw.println("<td>" +item.getItemName() + "</td>");
                pw.println("</tr>");
            }
        } catch (Exception e) {
            throw new ServletException(e);
        }
        pw.println("</table>");
    }
}

A regular Java SE project:

package com.company.app.logic;

import java.sql.ResultSet;
import java.sql.SQLException;

public class Item {

    private int itemId;
    private String itemName;

    public Item(ResultSet rs) {
        try {
            this.itemId = rs.getInt(1);
            this.itemName = rs.getString(2);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public String getItemName() {
        return itemName;
    }

    public int getItemId() {
        return itemId;
    }

    public String toString() {
        return itemName;
    }
}


package com.company.app.logic;
import java.sql.*;
import java.util.*;
public class Main {
    private static Main instance = new Main();
    private static Connection connection;
    private Main() {
       try {

           String url = "jdbc:mysql://localhost:3306/maindb";
           connection = DriverManager.getConnection(url, "root", "root");
       } catch (Exception e) {
           e.printStackTrace();
       }
    }
    public static Main getInstance() {
        return instance;
    }
    public List<Item> getItems() {
        List<Item> items = new ArrayList<>();
        Statement statement = null;
        ResultSet rs = null;
        try {
            statement = connection.createStatement();
            rs = statement.executeQuery("SELECT * FROM items");
            while (rs.next()) {
                Item g = new Item(rs);
                items.add(g);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (statement != null) {
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return items;
    }

    public static void main(String[] args) {
        Main m = Main.getInstance();
        m.getItems().forEach(System.out::println) 
    }
}