JSF Content of Database not loaded

Question

I have an issue with loding content from my database into Jakarta Faces.

The following Java Code should get the data and load into home.xhtml:

CarController.java

package com.ffhs.carsharing_v2.controllers;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import com.ffhs.carsharing_v2.helpers.CarsHelper;
import com.ffhs.carsharing_v2.pojos.Cars;

import jakarta.faces.application.FacesMessage;
import jakarta.faces.context.FacesContext;
import jakarta.inject.Named;


@Named
public class CarController implements Serializable {

    private static final long serialVersionUID = 1L;
    private List<Cars> cars;
    private CarsHelper carsHelper;

    public CarController() throws Exception {
        cars = new ArrayList<Cars>();
        carsHelper = CarsHelper.getInstance();
    }

    public List<Cars> getCars() {
        return cars;
    }

    public void loadCars () {
        cars.clear();
        try {
            cars = carsHelper.getCars();
        }catch (Exception e) {
            addErrorMessage (e);
        }
    }

    private void addErrorMessage(Exception ex) {
        FacesMessage message = new FacesMessage(ex.getMessage());
        FacesContext.getCurrentInstance().addMessage(null, message);
    }
}

CarsHelper

package com.ffhs.carsharing_v2.helpers;

import com.ffhs.carsharing_v2.pojos.Cars;
import com.ffhs.carsharing_v2.utilities.DataConnection;


import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

public class CarsHelper {
    private static CarsHelper instance;
       
    public static CarsHelper getInstance() throws Exception {
        if (instance == null) {
            instance = new CarsHelper();
        }
        return instance;
    }
  
    public List<Cars> getCars() throws Exception {
        List<Cars> cars = new ArrayList<>();
        Connection connection = null;
        PreparedStatement carsStatement;

        try {
            connection = DataConnection.getConnection();
            carsStatement = connection.prepareStatement("select * from cars");
                        ResultSet rs = carsStatement.executeQuery();

            while(rs.next()) {
                String carManufacturer = rs.getString("carManufacturer");
                String carModel = rs.getString("carModel");
                String carType = rs.getString("carType");
                String plateNumber = rs.getString("plateNumber");
                String status = rs.getString("status");

                Cars car = new Cars(carManufacturer, carModel,carType,plateNumber,status);
                cars.add(car);
            }
            return cars;
        }
        catch(Exception e) {
            System.out.println(e.getClass().getName() + ": " + e.getMessage());
            return null;
        }
        finally {
            DataConnection.close(connection);
        }
    }
}

Cars.java

package com.ffhs.carsharing_v2.pojos;

public class Cars {

   private String carManufacturer;

    private String carModel;

    private String carType;

    private String plateNumber;

    private String status;

    public Cars(String carManufacturer, String carModel, String carType, String plateNumber, String status) {
        this.carManufacturer = carManufacturer;
        this.carModel = carModel;
        this.carType = carType;
        this.plateNumber = plateNumber;
        this.status = status;
    }

    public String getCarManufacturer(){
        return carManufacturer;
    }

    public void setCarManufacturer(){
        this.carManufacturer = carManufacturer;
    }


    public String getCarModel() {
        return carModel;
    }

    public void setCarModel(String carModel) {
        this.carModel = carModel;
    }

    public String getCarType() {
        return carType;
    }

    public void setCarType(String carType) {
        this.carType = carType;
    }

    public String getPlateNumber() {
        return plateNumber;
    }

    public void setPlateNumber(String plateNumber) {
        this.plateNumber = plateNumber;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }
}

DataConnection.java

package com.ffhs.carsharing_v2.utilities;

import java.sql.*;
public class DataConnection
{
    public static Connection getConnection()
    {
        try {
            // Set up connection
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/carsharing", "root", "root");
            return connection;
        } catch (Exception e) {
            System.out.println(e.getClass().getName() + ": " + e.getMessage());
            return null;
        }
    }

    public static void close(Connection connection)
    {
        try {
            connection.close();
        } catch (Exception e) {

        }
    }
}

home.xhtml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
      xmlns:f="http://xmlns.jcp.org/jsf/core">

<h:head>
    <title>Car Reservation System - Home</title>
    <h:outputStylesheet name="css/footer.css" />
    <h:outputStylesheet name="css/home.css" />
    <h:outputStylesheet name="css/header.css" />
    <h:outputStylesheet library="webjars" name="font-awesome/6.2.0/css/all.min-jsf.css" />
</h:head>
<h:body>
    <ui:insert name="header">
    <ui:include src="templates/commonHeader.xhtml"></ui:include>
    </ui:insert>

    <div class="content">
        <h1> Welcome #{login.username}</h1>

        <div>
            <h2>Employees List</h2>
            <hr/>
            <h:dataTable value="#{carController.loadCars()}" var="car" border="1">

                <h:column>

                    <f:facet name="header">Manufacturer</f:facet>
                    #{car.carManufacturer}

                </h:column>
                <h:column>

                    <f:facet name="header">Model</f:facet>
                    #{car.carModel}

                </h:column>
                <h:column>

                    <f:facet name="header">Type</f:facet>
                    #{car.carType}

                </h:column>
                <h:column>

                    <f:facet name="header">Plate Number</f:facet>
                    #{car.plateNumber}

                </h:column>
                <h:column>

                    <f:facet name="header">Status</f:facet>
                    #{car.status}

                </h:column>
            </h:dataTable>

            <h:messages />
        </div>
    </div>




    <ui:insert name="footer">
        <ui:include src="templates/commonFooter.xhtml"></ui:include>
    </ui:insert>
</h:body>

</html>

The full code is available on https://github.com/ArisAccola/carsharing

Hope that somebody can assist me despite the enourmous quantity of code ;)

Thanks

score 1 · Accepted Answer · answered Nov 18 '22 at 19:31

The value of your data-table points to a method which returns nothing. Change the value to

<h:dataTable value="#{carController.cars}" var="car" border="1">

From now on, getCars() will be called to get the list of cars.

This leads to a new problem: carsController hasn't yet loaded the cars. You can do this from within your constructor, but it's better to use a lifecycle method:

@PostConstruct
public void setup() {
    if (cars == null) {
        loadCars();
    }
}

In loadCars() don't clear the list. This is not neccessary as you replace the whole list:

public void loadCars () {
    try {
        cars = carsHelper.getCars();
    }catch (Exception e) {
        addErrorMessage (e);
    }
}

And, you should not place your bean in the default scope (that's the 'dependent scope' for CDI beans). See this answer for details.

I hope, that I haven't missed anything.

Thanks. The project still not loads the data from the database. I tried to print out the loaded strings to the console whilst loaded from the database but it seems they are not even loaded as there is no output on the console as far as I can see. The database contains elements as follows: [table cars][1] The database connection itselfs seems working otherwise the login would not be even able. I have pushed the amended project to [Github][2] Any other idea? [1]: https://i.stack.imgur.com/Ahp9e.png [2]: https://github.com/ArisAccola/carsharing — Aris Martin Accola, Nov 19 '22 at 08:13
You have to remove `cars = new ArrayList<>()` from you constructor, because otherwise `cars` will never be `null` in `setup()`. — Mihe, Nov 19 '22 at 11:43

JSF Content of Database not loaded

1 Answers1