test_db.jspからtest_db.javaの表示までは上手く行くのですが、それ以降が結果反映されません。Eclipse ver.2019-03(4.11.0)を使っています。

ご回答よろしくお願いします。

test_db.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>ユーザー登録</title>
</head>
<body>
<form action="test_db" method="post">
名前:<br>
<input type="text" name="name"><br>
性別:<br>
男<input type="radio" name="gender" value="0">
女<input type="radio" name="gender" value="1">
<input type="submit" value="登録">
</form>
</body>
</html>

test_db.java

package servlet;

import java.io.IOException;
import java.io.PrintWriter;

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

/**
 * Servlet implementation class FormSampleServlet
 */
@WebServlet("/test_db")
public class test_db extends HttpServlet {
    private static final long serialVersionUID = 1L;

    //インスタンス化　値受け渡し
    //ConnectionClass obj = new ConnectionClass();

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */

    static final String URL = "jdbc:mysql://localhost/data_data";
    static final String USERNAME = "rararaio";
    static final String PASSWORD = "Vwxyz123";

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //リクエストパラメータを取得
        request.setCharacterEncoding("UTF-8");
        String name = request.getParameter("name");
        String gender = request.getParameter("gender");

        //リクエストパラメータをチェック
        String errorMsg = "";
        if(name == null || name.length() == 0) {
            errorMsg += "名前が入力されていません<br>";
        }
        if(gender == null || gender.length() == 0) {
            errorMsg += "性別が選択されていません<br>";
        } else {
            if(gender.equals("0")) {
                gender = "男性";
            } else if(gender.equals("1")) {
                gender = "女性";
            }
        }

        //表示するメッセージ
        String msg = "'" + name + "','" + gender + "'";
        if(errorMsg.length() != 0) {
            msg = errorMsg;
        }

        //HTMLを出力
        response.setContentType("text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<meta charset=\"UTF-8\">");
        out.println("<title>ユーザー登録結果</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<p>"+msg+"</p>");
        out.println("</body>");
        out.println("</html>");

    }

}

test_db_connection.java

package com.developersio;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class test_db_connection {

    static final String URL = "jdbc:mysql://localhost/data_data";
    static final String USERNAME = "rararaio";
    static final String PASSWORD = "Vwxyz123";

    public static void main(String[] args) {

        try (
                Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
                Statement statement = connection.createStatement();
                ) {

            String sql = "INSERT INTO test VALUES (msg);";
//          String sql = "INSERT INTO test VALUES ('matuda','man');";
            int result = statement.executeUpdate(sql);
            System.out.println("結果１：" + result);

//            sql = "INSERT INTO music (name, title, year) VALUES ('Aril');";
            sql = "INSERT INTO test VALUES ('tanaka','woman');";
            result = statement.executeUpdate(sql);
            System.out.println("結果２：" + result);

        } catch (SQLException e) {

            e.printStackTrace();

        }

    }

}