java - 如何用Java从数据库中检索每一行和每一列的数据

Question

我是 Java 新手。我如何从数据库中检索数据并将其放入某个变量中。我考虑过数组，但数据有多种类型。并且数据的检索是使用另一个类的方法。

我得到了使用 ArrayList 的提示，但我不知道如何使用它。对我有什么线索或建议吗？

这是主要方法:

class JavaAppsTes {
   public static void main(String[] args) { 
      Database app = new Database();

      /* I don't know what to do here */
   }   

这是数据库类:

public void getMenu() {
    String SQL = "SELECT * FROM menu ORDER by id_kategori";
    String nama, gambar;
    int id_menu, id_kategori, harga, persediaan;
    int count = 0;

    try (Connection conn = connect(); Statement stmt = conn.createStatement(); ResultSet cartRslt = stmt.executeQuery(SQL)) {
        while(cartRslt.next()) {
            id_menu = cartRslt.getInt("id_menu");
            id_kategori = cartRslt.getInt("id_kategori");
            harga = cartRslt.getInt("harga");
            persediaan = cartRslt.getInt("persediaan");
            nama = cartRslt.getString("nama");
            gambar = cartRslt.getString("gambar"); 
        }
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }
}

如何将这些数据放入某些内容中，以便前端可以使用检索到的数据？

顺便说一句，自从我得到了有关 ArrayList 的线索后，我创建了一些像这样的菜单类:

public class Menu {
    private int id_menu;
    private int id_kategori;
    private String nama;
    private int harga;
    private int persediaan;
    private String gambar;

    public Menu(int id_menu, int id_kategori, String nama, int harga, int persediaan, String gambar) {
        this.id_menu = id_menu;
        this.id_kategori = id_kategori;
        this.nama = nama;
        this.harga = harga;
        this.persediaan = persediaan;
        this.gambar = gambar;
    }

    public int getid_menu(){
       return id_kategori;
    }

    public void setid_menu(int id_menu){
        this.id_menu = id_menu;
    }

    public int getid_kategori(){
       return id_kategori;
    }

    public void setid_kategori(int id_kategori){
        this.id_kategori = id_kategori;
    }

    public String getnama(){
        return nama;
    }

    public void setnama(String nama){
        this.nama = nama;
    }

    public int getharga(){
        return harga;
    }

    public void setharga(int harga){
        this.harga = harga;
    }

    public int getpersediaan(){
        return persediaan;
    }

    public void setpersediaan(int persediaan){
        this.persediaan = persediaan;
    }

    public String getgambar(){
        return gambar;
    }

    public void setgambar(String gambar){
        this.gambar = gambar;
    }
}

Answer 1

如果您需要 ArrayList 在循环之前定义它，请添加每个菜单并在之后返回它。

public ArrayList<Menu> getMenu() {
String SQL = "SELECT * FROM menu ORDER by id_kategori";
String nama, gambar;
int id_menu, id_kategori, harga, persediaan;
int count = 0;
ArrayList<Menu> arr = new ArrayList<>();
try (Connection conn = connect(); 
Statement stmt = conn.createStatement(); 
ResultSet cartRslt = stmt.executeQuery(SQL)) {
    while(cartRslt.next()) {
        id_menu = cartRslt.getInt("id_menu");
        id_kategori = cartRslt.getInt("id_kategori");
        harga = cartRslt.getInt("harga");
        persediaan = cartRslt.getInt("persediaan");
        nama = cartRslt.getString("nama");
        gambar = cartRslt.getString("gambar"); 
       arr.add(new Menu(id_menu, id_kategori, nama, harga, persediaan, gambar));
 }
 }
return arr;
}