Почему срабатывает insert при перезагрузке JSP страницы?

<%@ page language="java" %> 
<%@ page import="java.sql.*, java.io.*, java.text.*, java.util.Date, java.Math.*, java.math.RoundingMode" %>
<%@page contentType="text/html; charset=UTF-8"%>

    <input id="user_location" type="text" value="?" style="display:none">
    <c:set var="NUM" value='<%= request.getParameter("NUM") %>'/>
    <c:set var="SOLUTION" value='<%= request.getParameter("SOLUTION") %>'/>
    <c:if test="${NUM==null}">
        <c:set var="NUM" value="7"/>
        <c:set var="SOLUTION" value="Быстрый пример"/>
    </c:if>
        <%!
private static class Insert_In_DB {
private String Insert_to_MySQL(String NUM, String SOLUTION) throws UnsupportedEncodingException {
String Insert_to_MySQL;
String Insert_Text;
Insert_to_MySQL="";
Insert_Text="";
        try {
 	    Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
        Insert_to_MySQL="Драйвер не найден!";
        }
	try {
	    Connection conn = DriverManager.getConnection ("jdbc:mysql://хост:порт/", "имя", "пароль" );
Insert_Text = "insert into test.example (num, solution) VALUES (?, ?)";
      PreparedStatement preparedStmt = conn.prepareStatement(Insert_Text);
      preparedStmt.setString (1, NUM);
      preparedStmt.setString (2, SOLUTION);
      preparedStmt.execute();
            conn.close();
            Insert_to_MySQL="Insert выполнен.";
        } catch (Exception e) {
          Insert_to_MySQL=Insert_to_MySQL+" "+Insert_Text+" НЕ выполнен. Ошибка:"+e.getMessage();
        }
return Insert_to_MySQL;
}
}
%>

<script type="text/javascript">
$(function(){
    var local = $('#user_location').val();
    $('#insert_to_mysql').on('click', function () {
        console.log('Нажали кнопку insert_to_mysql');
        var NUM=document.getElementById('num').value;
        var SOLUTION=document.getElementById('solution').value;
        console.log("<%=new Insert_In_DB().Insert_to_MySQL(pageContext.getAttribute("NUM", PageContext.PAGE_SCOPE).toString(),pageContext.getAttribute("SOLUTION", PageContext.PAGE_SCOPE).toString())%>");
        window.location.replace(local+"&NUM="+NUM+"&SOLUTION="+SOLUTION);
    })
})
</script>

    <input id="num" name="num" type="text" size="10" value="${NUM}">
    <input id="solution" name="solution" type="text" size="30" value="${SOLUTION}">

     <button id="insert_to_mysql" class="btn btn-primary">Insert в MySQL</button>