java - 在 Vaadin 中如何显示连接表中的数据？

Question

我使用 JavaEE 在页面上显示所有产品数据和Vaadin除了类别列显示整个对象而不仅仅是类别名称之外，它正在工作。

我正在连接两个表 product和category基于category_id列并从 category 获取并显示类别名称 table 。 ProductDaoImpl中提到了查询下面的类(class)。

POM 中的 Vaadin 版本

<vaadin.version>7.6.5</vaadin.version>

ProductsUI.java

@Title("Home")
@Theme("mytheme")
@Widgetset("com.study.crud.MyAppWidgetset")
public class ProductsUI extends UI {

    private static final Logger LOG = Logger.getLogger(ProductsUI.class);
    private final Grid productsGrid = new Grid();
    private DataSource dataSource;

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        getDataSource(vaadinRequest);
        configureComponents();
        buildLayout();
    }

    private void getDataSource(VaadinRequest vaadinRequest) {
        VaadinServletRequest req = (VaadinServletRequest) vaadinRequest;
        this.dataSource = (DataSource) req.getServletContext().getAttribute("dataSource");
    }

    private void configureComponents() {
        // get all products
        ProductDao productDao = new ProductDaoImpl(dataSource);
        List<Product> products = productDao.getProducts();

        //set all the products in grid
        productsGrid.setContainerDataSource(new BeanItemContainer<>(Product.class, products));
        productsGrid.setColumnOrder("productId", "name", "image", "listPrice", "category", "active");
        productsGrid.removeColumn("description");
        productsGrid.removeColumn("createdBy");
        productsGrid.removeColumn("expiryDate");
        productsGrid.removeColumn("modifiedOn");
    }

    private void buildLayout() {
        VerticalLayout layout = new VerticalLayout();

        //add products grid to the main layout
        layout.addComponent(productsGrid);
        productsGrid.setSizeFull();
        layout.setSizeFull();
        layout.setMargin(true);
        layout.setSpacing(true);

        setContent(layout);
    }

    @WebServlet(urlPatterns = "/*", name = "ProductsUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = ProductsUI.class, productionMode = false)
    public static class ProductsUIServlet extends VaadinServlet {
    }

}

产品.java

public class Product implements Serializable {

    private int productId;
    private String name;
    private String description;
    private String image;
    private BigDecimal listPrice;
    private Category category;
    private Date expiryDate;
    private String createdBy;
    private Date modifiedOn;
    private String active;

    public Product() {
    }

    public Product(int productId) {
        this.productId = productId;
    }

    public Product(int productId, String name, String description, String image, BigDecimal listPrice, Category category, Date expiryDate, String createdBy, Date modifiedOn, String active) {
        this.productId = productId;
        this.name = name;
        this.description = description;
        this.image = image;
        this.listPrice = listPrice;
        this.category = category;
        this.expiryDate = expiryDate;
        this.createdBy = createdBy;
        this.modifiedOn = modifiedOn;
        this.active = active;
    }

    public int getProductId() {
        return productId;
    }

    public void setProductId(int productId) {
        this.productId = productId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }

    public BigDecimal getListPrice() {
        return listPrice;
    }

    public void setListPrice(BigDecimal listPrice) {
        this.listPrice = listPrice;
    }

    public Category getCategory() {
        return category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    public Date getExpiryDate() {
        return expiryDate;
    }

    public void setExpiryDate(Date expiryDate) {
        this.expiryDate = expiryDate;
    }

    public String getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(String createdBy) {
        this.createdBy = createdBy;
    }

    public Date getModifiedOn() {
        return modifiedOn;
    }

    public void setModifiedOn(Date modifiedOn) {
        this.modifiedOn = modifiedOn;
    }

    public String getActive() {
        return active;
    }

    public void setActive(String active) {
        this.active = active;
    }

    @Override
    public String toString() {
        return "Product{" + "productId=" + productId + ", name=" + name + ", description=" + description + ", image=" + image + ", listPrice=" + listPrice + ", category=" + category + ", expiryDate=" + expiryDate + ", createdBy=" + createdBy + ", modifiedOn=" + modifiedOn + ", active=" + active + '}';
    }

}

类别.java

public class Category implements Serializable {

    private int categoryId;
    private String name;
    private String description;
    private Date expiryDate;
    private String createdBy;
    private Date modifiedOn;
    private String active;

    public Category() {
    }

    public Category(int categoryId) {
        this.categoryId = categoryId;
    }

    public Category(String name) {
        this.name = name;
    }

    public Category(int categoryId, String name) {
        this.categoryId = categoryId;
        this.name = name;
    }

    public Category(int categoryId, String name, String description, Date expiryDate, String createdBy, Date modifiedOn, String active) {
        this.categoryId = categoryId;
        this.name = name;
        this.description = description;
        this.expiryDate = expiryDate;
        this.createdBy = createdBy;
        this.modifiedOn = modifiedOn;
        this.active = active;
    }

    public int getCategoryId() {
        return categoryId;
    }

    public void setCategoryId(int categoryId) {
        this.categoryId = categoryId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Date getExpiryDate() {
        return expiryDate;
    }

    public void setExpiryDate(Date expiryDate) {
        this.expiryDate = expiryDate;
    }

    public String getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(String createdBy) {
        this.createdBy = createdBy;
    }

    public Date getModifiedOn() {
        return modifiedOn;
    }

    public void setModifiedOn(Date modifiedOn) {
        this.modifiedOn = modifiedOn;
    }

    public String getActive() {
        return active;
    }

    public void setActive(String active) {
        this.active = active;
    }

    @Override
    public String toString() {
        return "Category{" + "categoryId=" + categoryId + ", name=" + name + ", description=" + description + ", expiryDate=" + expiryDate + ", createdBy=" + createdBy + ", modifiedOn=" + modifiedOn + ", active=" + active + '}';
    }

}

ProductDaoImpl.java

public class ProductDaoImpl implements ProductDao {

    private final DataSource dataSource;

    public ProductDaoImpl(DataSource dataSource) {
        this.dataSource = dataSource;
    }


    @Override
    public List<Product> getProducts() {
        String sql = "select a.*, b.name as category_name from product a, category b where a.category_id = b.category_id";
        LOG.debug(sql);

        Statement stmt = null;
        ResultSet rs = null;
        Connection cn = null;
        List<Product> products = new ArrayList<>();
        try {
            cn = dataSource.getConnection();
            stmt = cn.createStatement();
            rs = stmt.executeQuery(sql);
            while (rs != null && rs.next()) {
                int productId = new Integer(StringUtils.defaultString(rs.getString("PRODUCT_ID")));
                String name = StringUtils.defaultString(rs.getString("NAME"));
                String description = StringUtils.defaultString(rs.getString("DESCRIPTION"));
                String image = StringUtils.defaultString(rs.getString("IMAGE"));
                BigDecimal listPrice = new BigDecimal(StringUtils.defaultString(rs.getString("LIST_PRICE")));
                int categoryId = new Integer(StringUtils.defaultString(rs.getString("CATEGORY_ID")));
                String categoryName = StringUtils.defaultString(rs.getString("CATEGORY_NAME"));
                Category category = new Category(categoryId, categoryName);
                Date expiryDate = rs.getDate("EXPIRY_DATE");
                String createdBy = StringUtils.defaultString(rs.getString("CREATED_BY"));
                Date modifiedOn = rs.getDate("MODIFIED_ON");
                String active = StringUtils.defaultString(rs.getString("ACTIVE"));
                Product product = new Product(productId, name, description, image, listPrice, category, expiryDate, createdBy, modifiedOn, active);
                products.add(product);
            }
            LOG.debug("products = " + products);
            LOG.debug("products.size() = " + products.size());
            return products;
        } catch (SQLException | NumberFormatException ex) {
            LOG.error("Exception while getting products....", ex);
            return null;
        } //close resources
        finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (stmt != null) {
                    stmt.close();
                }
                if (cn != null) {
                    cn.close();
                }
            } catch (SQLException ex) {
                LOG.error("Exception while closing DB resources rs, stmt or cn.......", ex);
            } finally {
                try {
                    if (cn != null) {
                        cn.close();
                    }
                } catch (SQLException ex) {
                    LOG.error("Exception while closing cn.......", ex);
                }
            }
        }
    }
}

Answer 1

原因是(因为您使用 BeanItemContainer)Vaadin 调用 Product 类中的每个 getter 并尝试将每个返回值转换为 String*。当它到达 Category getter 时，它会对返回值调用 toString()。由于您已重写 Category 中的 toString() 方法，Vaadin 会调用该方法并在 Grid 中显示返回值。如果您在 Category 类中保持 toString() 方法不变，它将显示 Object.toString() 返回的值。

解决此特定问题的简单方法是在您的 Product 类中添加此 getter:

public String getCategoryName() {
    return category.getName();
}

并删除“类别”列。

*_{当我们考虑列的转换器时，情况并不总是如此，但在这种情况下它已经足够好了}