在 Vaadin 网格中显示来自 SQL 的数据

Question

我试图在我的网格中显示我的 SQL table 数据，但似乎没有任何效果。你能指出我错在哪里吗？

我在互联网上找到了很多方法，但 none 对我有用。希望你能找到问题并帮助我。

我正在使用：带有 Spring 引导的 Vaadin 14

CustomerService.java

@Component
public class CustomerService {
    @Autowired
    private JdbcTemplate jdbcTemplate;

    public List<Customer> findAll() {
        return jdbcTemplate.query(
                "SELECT ID, FirstName, LastName FROM customer",
                (rs, rowNum) -> new Customer(rs.getLong("id"),
                        rs.getString("First Name"), rs.getString("Last Name")));
    }

    public void update(Customer customer) {
        jdbcTemplate.update("INSERT INTO customer (FirstName,LastName) VALUES(?,?)",customer.getFirstName(),customer.getLastName());


    }
}

MainView.Java

public class MainView extends VerticalLayout {
    @Autowired
    private CustomerService service ;
    public Customer customer = new Customer();
    private Binder<Customer> binder = new Binder<>(Customer.class);
    private TextField firstName = new TextField("First name");
    private TextField lastName = new TextField("Last name");

    private Grid<Customer> grid = new Grid(Customer.class);
    private  Button save = new Button("Save", e -> {
        try {
            binder.writeBean(customer);
            saveCustomer();
            binder.readBean(new Customer());
        } catch (ValidationException ex) {
            ex.printStackTrace();
        }
    });

    public MainView(CustomerService service) {
       add(
                new H1("הוסף לקוח"),
               buildForm(),
               grid
       );
       updateGrid(); // update the grid with the sql data

        setSizeFull();


    }
    private void saveCustomer() throws ValidationException {

        service.update(customer);

    }
    private Component buildForm() {

       // TextField id = new TextField("ID");
        TextField firstName = new TextField("First name");
         TextField lastName = new TextField("Last name");
        Div errorsLayout = new Div();

binder.forField(firstName)
        .bind(
                Customer::getFirstName,Customer::setFirstName
        );
        binder.forField(lastName)
                .bind(
                        Customer::getLastName,Customer::setLastName
                );



        Button reload = new Button("reload", e ->{
            try{
                binder.readBean(customer);
               
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        });
        // Configure UI components
        save.setThemeName("primary");
        // Wrap components in layouts
        HorizontalLayout formLayout = new HorizontalLayout(grid,firstName,lastName,save,reload);
        Div wrapperLayout = new Div(formLayout, errorsLayout);
        formLayout.setDefaultVerticalComponentAlignment(Alignment.BASELINE);
        wrapperLayout.setWidth("100%");

        grid.setColumnReorderingAllowed(true);

        
        return wrapperLayout;

    }


    private void updateGrid() {
        List<Customer> customers = service.findAll();
        grid.setItems(customers);



    }

我得到的错误：

There was an exception while trying to navigate to '' with the exception message 'Error creating bean with name 'com.packagename.myapp.spring.MainView': Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.packagename.myapp.spring.MainView]: Constructor threw exception; nested exception is java.lang.NullPointerException'

Answer 1

您永远不会设置 CustomerService 字段。添加

this.service = service;

到构造函数的开头。否则成员字段 private CustomerService service 将为空，这就是 updateGrid 抛出 NullPointerException.

的原因

此外，作为旁注，从成员字段中删除 @Autowired 注释。您混合了两种不同的自动装配方式，一种是自动装配字段

@Autowired
private CustomerService service;

public MainView() { ... }

在这种情况下，Spring 会自动为您设置值，并且不会作为参数传递给构造函数。但是，Spring 将它设置在构造函数之后，因此您不能在构造函数中或从构造函数调用的任何方法中使用它。

另一种方法是构造函数自动装配，这是你应该做的。在这种情况下 Spring 将 bean 传递给构造函数，但如果需要，您需要自己设置成员字段。

private CustomerService service;

@Autowired
public MainView(CustomerService service) {
    this.service = service;
    ...
}

构造函数前不需要 @Autowired 批注，没有它也能正常工作，但如果需要，为了清楚起见，可以将它放在那里。

在 Vaadin 网格中显示来自 SQL 的数据

Show data from SQL in Vaadin Grid

java

vaadin

spring-boot

vaadin-grid