Can not write data to TableView in JavaFXML after read from .json-file

Question

my propblem is, that I have a List that is an ArrayList that is filled with my Objects called Daten, which I save in a .json-file

    PopUp pop = new PopUp();
    Gson gson = new GsonBuilder().create();
    JsonWriter writer = new JsonWriter(new FileWriter(new File(System.getProperty("user.home"), "/Wirtschaft.json")));
    gson.toJson(allEntries, List.class, writer);
    try {
        writer.flush();
        writer.close();
        pop.show("Saved!");
    } catch (IOException e) {
        pop.show("Trying to save data failed!");
    }

To use the list of Daten again I read everything from the .json-file and save it in a List<Daten>

Gson gson = new GsonBuilder().create();
    List<Daten> allSaves = new ArrayList<>();
    if (new File(System.getProperty("user.home"), "/Wirtschaft.json").exists()) {
        JsonReader jReader = new JsonReader(new FileReader(new File(System.getProperty("user.home"), "/Wirtschaft.json")));

        BufferedReader br = new BufferedReader(new FileReader(new File(System.getProperty("user.home"), "/Wirtschaft.json")));
        if (br.readLine() != null) {
            allSaves = gson.fromJson(jReader, List.class);
        }
        br.close();
        jReader.close();
    }

    return allSaves;

Now I want to display this List in a TableView like this:

ObservableList<Daten> listEntries = FXCollections.observableArrayList(Daten.readData());

    columnGewicht.setCellValueFactory(new PropertyValueFactory<>("gewicht"));
    columnPreis.setCellValueFactory(new PropertyValueFactory<>("preisProStueck"));
    columnGewinn.setCellValueFactory(new PropertyValueFactory<>("gewinn"));
    columnEB.setCellValueFactory(new PropertyValueFactory<>("eb"));
    columnAKK.setCellValueFactory(new PropertyValueFactory<>("akk"));
    columnSB.setCellValueFactory(new PropertyValueFactory<>("sb"));
    columnGK.setCellValueFactory(new PropertyValueFactory<>("gk"));
    columnBoni.setCellValueFactory(new PropertyValueFactory<>("boni"));

    table.setItems(listEntries);

Problem is, that the TableView remains empty when I use the code above, but if I don't use the Daten that I wrote in that file like above, it works and shows everything in the TableView, even if I choose the same numbers etc.:

List<Daten> list = new ArrayList<>();
    list.add(new Daten(100, 6, 421, 3, 4, 1, 6, 0));
    ObservableList<Daten> listEntries = FXCollections.observableArrayList(list);

    columnGewicht.setCellValueFactory(new PropertyValueFactory<>("gewicht"));
    columnPreis.setCellValueFactory(new PropertyValueFactory<>("preisProStueck"));
    columnGewinn.setCellValueFactory(new PropertyValueFactory<>("gewinn"));
    columnEB.setCellValueFactory(new PropertyValueFactory<>("eb"));
    columnAKK.setCellValueFactory(new PropertyValueFactory<>("akk"));
    columnSB.setCellValueFactory(new PropertyValueFactory<>("sb"));
    columnGK.setCellValueFactory(new PropertyValueFactory<>("gk"));
    columnBoni.setCellValueFactory(new PropertyValueFactory<>("boni"));

    table.setItems(listEntries);

How can I fix this, that the TableView does not show my Data that I read from the file? Like there can not be something wrong with the TableView, if this other methode works... I am unfortunately clueless.

Thanks in advance!

EDIT:

Here is the Class for Daten:

public class Daten {

private Double gewicht;
private Double preisProStueck;
private Double gewinn;
private Double eb;
private Double akk;
private Double sb;
private Double gk;
private Integer boni;

Daten(double gewicht, double preisProStueck, double gewinn, double EB, double AKK, double SB, double GK, int boni) {
    this.gewicht = gewicht;
    this.preisProStueck = preisProStueck;
    this.gewinn = gewinn;
    this.eb = EB;
    this.akk = AKK;
    this.sb = SB;
    this.gk = GK;
    this.boni = boni;
}

static List<Daten> readData() throws IOException {
    Gson gson = new GsonBuilder().create();
    List<Daten> allSaves = new ArrayList<>();
    if (new File(System.getProperty("user.home"), "/Wirtschaft.json").exists()) {
        JsonReader jReader = new JsonReader(new FileReader(new File(System.getProperty("user.home"), "/Wirtschaft.json")));

        BufferedReader br = new BufferedReader(new FileReader(new File(System.getProperty("user.home"), "/Wirtschaft.json")));
        if (br.readLine() != null) {
            allSaves = gson.fromJson(jReader, List.class);
        }
        br.close();
        jReader.close();
    }

    return allSaves;
}

private static void writeData(List<Daten> allEntries) throws IOException {
    PopUp pop = new PopUp();
    Gson gson = new GsonBuilder().create();
    JsonWriter writer = new JsonWriter(new FileWriter(new File(System.getProperty("user.home"), "/Wirtschaft.json")));
    gson.toJson(allEntries, List.class, writer);
    try {
        writer.flush();
        writer.close();
        pop.show("Zeugs wurde gespeichert!");
    } catch (IOException e) {
        pop.show("Trying to save data failed!");
    }
}

static void addData(Daten data) throws IOException {
    List<Daten> list = readData();
    list.add(data);
    writeData(list);
}

public Double getGewicht() {
    return gewicht;
}

public void setGewicht(Double gewicht) {
    this.gewicht = gewicht;
}

public Double getPreisProStueck() {
    return preisProStueck;
}

public void setPreisProStueck(Double preisProStueck) {
    this.preisProStueck = preisProStueck;
}

public Double getGewinn() {
    return gewinn;
}

public void setGewinn(Double gewinn) {
    this.gewinn = gewinn;
}

public Double getEb() {
    return eb;
}

public void setEb(Double eb) {
    this.eb = eb;
}

public Double getAkk() {
    return akk;
}

public void setAkk(Double akk) {
    this.akk = akk;
}

public Double getSb() {
    return sb;
}

public void setSb(Double sb) {
    this.sb = sb;
}

public Double getGk() {
    return gk;
}

public void setGk(Double gk) {
    this.gk = gk;
}

public Integer getBoni() {
    return boni;
}

public void setBoni(Integer boni) {
    this.boni = boni;
}}