private Connection conn;
private PreparedStatement pstmt;
private ResultSet rs;
private int rs2 = 0;

public UserDAO() {
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/ajax", "root", "!pretty124");
        // conn.setAutoCommit(false);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

void disconnect() {
    if (pstmt != null) {
        try {
            pstmt.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    if (conn != null) {
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

public String join_insert(String id, String pw, String name, String age, String gender, String hobby, String email,
        String phone) throws SQLException {
    String sql = "INSERT INTO test VALUES(?, ?, ?, ?, ?, ?, ?, ?)";
    try {
        System.out.println("success.");
        pstmt = conn.prepareStatement(sql);
        pstmt.setString(1, id);
        pstmt.setString(2, pw);
        pstmt.setString(3, name);
        pstmt.setInt(4, Integer.parseInt(age));
        pstmt.setString(5, gender);
        pstmt.setString(6, hobby);
        pstmt.setString(7, email);
        pstmt.setString(8, phone);

        rs2 = pstmt.executeUpdate();
    } catch (Exception e) {
        e.printStackTrace();
        return "";
    } finally {
        disconnect();
    }

    return "";
}

request.open("Post","./JoinInsertServlet?id="
            +encodeURIComponent(document.getElementById("join_info_id").value)