I’m using JavaFX and my combobox doesn’t want to populate from an sql database

What I’m trying to do is have my combobox get populated with AgentID’s from my travelexperts database when the app loads.

I think the problem is somewhere in the controller class. I don’t get any exceptions but if I try to run the buildCombo() method from one of the buttons instead of initialize I get a class not found exception

Controller class:

package sample;

import java.net.URL;
import java.sql.*;
import java.util.ResourceBundle;

import javafx.beans.Observable;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.TextField;
import javafx.scene.input.MouseEvent;

public class Controller {

    Connection conn;

    @FXML
    private ResourceBundle resources;

    @FXML
    private URL location;

    @FXML
    private TextField tvAgentID;

    @FXML
    private TextField tvFirstName;

    @FXML
    private TextField tvMiddleInitial;

    @FXML
    private TextField tvLastName;

    @FXML
    private TextField tvPhone;

    @FXML
    private TextField tvEmail;

    @FXML
    private TextField tvPosition;

    @FXML
    private TextField tvAgencyID;

    @FXML
    private Button btnSave;

    @FXML
    private Button btnEdit;

    @FXML
    private ComboBox cmbAgentID;

    public Controller() throws SQLException {
    }

    @FXML
    void cmbClicked(MouseEvent event) {

    }

    @FXML
    void editClicked(MouseEvent event) {

    }

    @FXML
    void saveClicked(MouseEvent event) throws SQLException, ClassNotFoundException {
        updateAgent();
    }



    /////////////////////////////METHODS/////////////////////


    private void buildCombo() throws SQLException, ClassNotFoundException {
        // TODO Auto-generated method stub
        Connection conn;
        Class.forName("com.mysql.cj.jdbc.Driver");

        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/travelexperts",
                "Sander", "********");
        ObservableList<Agent> data = FXCollections.observableArrayList();
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("select AgentId from agents");
        while (rs.next()) {
            data.add(new Agent(rs.getInt("agentID")));
        }
        cmbAgentID.setItems(data);
    }

    ///////////////////INITIALIZE/////////////////////////////
    @FXML
    public void initialize(URL location, ResourceBundle resources) throws SQLException, ClassNotFoundException {
        assert tvAgentID != null : "fx:id="tvAgentID" was not injected: check your FXML file 'sample.fxml'.";
        assert tvFirstName != null : "fx:id="tvFirstName" was not injected: check your FXML file 'sample.fxml'.";
        assert tvMiddleInitial != null : "fx:id="tvMiddleInitial" was not injected: check your FXML file 'sample.fxml'.";
        assert tvLastName != null : "fx:id="tvLastName" was not injected: check your FXML file 'sample.fxml'.";
        assert tvPhone != null : "fx:id="tvPhone" was not injected: check your FXML file 'sample.fxml'.";
        assert tvEmail != null : "fx:id="tvEmail" was not injected: check your FXML file 'sample.fxml'.";
        assert tvPosition != null : "fx:id="tvPosition" was not injected: check your FXML file 'sample.fxml'.";
        assert tvAgencyID != null : "fx:id="tvAgencyID" was not injected: check your FXML file 'sample.fxml'.";
        assert btnSave != null : "fx:id="btnSave" was not injected: check your FXML file 'sample.fxml'.";
        assert btnEdit != null : "fx:id="btnEdit" was not injected: check your FXML file 'sample.fxml'.";
        assert cmbAgentID != null : "fx:id="cmbAgentID" was not injected: check your FXML file 'sample.fxml'.";
        btnSave.setStyle("-fx-background-color: cornflowerblue");
        btnEdit.setStyle("-fx-background-color: cornflowerblue");
        try {
            conn = new DB().getConnection();
            buildCombo();
        } catch (ClassNotFoundException | SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

DB class:

package sample;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DB {

    public Connection getConnection() throws ClassNotFoundException, SQLException
    {
        Class.forName("com.mysql.jdbc.Driver");
        return DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/travelexperts",
                "Sander",
                "*******"
        );
    }
}

Main Class:

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root, 800, 500));
        primaryStage.show();
    }


    public static void main(String[] args) {
        launch(args);
    }
}

Sample class:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ComboBox?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <TextField fx:id="tvAgentID" layoutX="14.0" layoutY="52.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvFirstName" layoutX="143.0" layoutY="52.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvMiddleInitial" layoutX="290.0" layoutY="49.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvLastName" layoutX="447.0" layoutY="52.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvPhone" layoutX="24.0" layoutY="321.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvEmail" layoutX="161.0" layoutY="321.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvPosition" layoutX="317.0" layoutY="321.0" prefHeight="26.0" prefWidth="89.0" />
      <TextField fx:id="tvAgencyID" layoutX="475.0" layoutY="321.0" prefHeight="26.0" prefWidth="89.0" />
      <Label alignment="CENTER" layoutX="18.0" layoutY="11.0" prefHeight="26.0" prefWidth="81.0" text="AgentID" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="147.0" layoutY="14.0" prefHeight="26.0" prefWidth="81.0" text="First Name" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="294.0" layoutY="14.0" prefHeight="26.0" prefWidth="90.0" text="Middle Initial" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="451.0" layoutY="14.0" prefHeight="26.0" prefWidth="81.0" text="Last Name" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="28.0" layoutY="298.0" prefHeight="26.0" prefWidth="81.0" text="Phone" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="165.0" layoutY="298.0" prefHeight="26.0" prefWidth="81.0" text="Email" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="321.0" layoutY="298.0" prefHeight="26.0" prefWidth="81.0" text="Position" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label alignment="CENTER" layoutX="479.0" layoutY="298.0" prefHeight="26.0" prefWidth="81.0" text="AgencyID" textAlignment="CENTER">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <Label layoutX="14.0" layoutY="123.0" prefHeight="62.0" prefWidth="235.0" text="EDIT AN AGENT">
         <font>
            <Font name="System Bold" size="24.0" />
         </font>
      </Label>
      <Button fx:id="btnSave" layoutX="447.0" layoutY="126.0" mnemonicParsing="false" onMouseClicked="#saveClicked" prefHeight="56.0" prefWidth="120.0" text="Save" />
      <Button fx:id="btnEdit" layoutX="447.0" layoutY="200.0" mnemonicParsing="false" onMouseClicked="#editClicked" prefHeight="56.0" prefWidth="120.0" text="Edit" />
      <ComboBox fx:id="cmbAgentID" layoutX="235.0" layoutY="140.0" onMouseClicked="#cmbClicked" prefHeight="28.0" prefWidth="130.0" />
   </children>
</AnchorPane>

Agent Class:

package sample;

public class Agent {

    private int agentID;
    private String firstName;
    private String middleInitial;
    private String lastName;
    private String businessPhone;
    private String email;
    private String position;
    private int agencyID;

    //////////////Constructors////////////////

    public Agent(int agentID, String firstName, String middleInitial, String lastName,
                 String businessPhone, String email, String position, int agencyID) {
        this.agentID = agentID;
        this.firstName = firstName;
        this.middleInitial = middleInitial;
        this.lastName = lastName;
        this.businessPhone = businessPhone;
        this.email = email;
        this.position = position;
        this.agencyID = agencyID;
    }

    public Agent(int agentID) {
        this.agentID = agentID;
    }

Answer

In your DB Class you are using the right MySQL Driver but in your buildCombo() Method you are using wrong/deprecated driver for MySQL, change Class.forName("com.mysql.cj.jdbc.Driver"); to Class.forName("com.mysql.jdbc.Driver"); as you have in DB Class and it should work. Also, print out the ResultSet rs in the console, so you are sure that you are having some result there.