Question

我正在用JSF建立一个简单的电子商店。有一个包含所有产品列表的页面（product-list.xhtml），然后是每个产品的详细信息页面（product.xhtml）。 product-list.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>

</h:head>
<h:body>
    <f:view>
        <h:outputText value="Number of items in the cart: #{shoppingCart.numberOfSelectedProducts}"/>
        <h:link value="Cart" outcome="cart.xhtml"/>

        <h:dataTable value="#{productController.products}" var="p">
            <h:column>
                #{p.name}
                <h:commandLink action="product.xhtml" value="Detail">
                    <f:actionListener target="#{product.id}" value="#{p.id}"/>
                </h:commandLink>
            </h:column>

            <h:column>

            </h:column>
        </h:dataTable>
    </f:view>
</h:body>

</html>

然后product.xhtml看起来如下：

<?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">
<head></head>
<!--f:metadata>
    <f:event type="preRenderView" listener="#{shoppingCart.loadSelectedProduct(param.id)}"/>
</f:metadata -->
<body>
    <f:view>
        <h:graphicImage value="resources/images/img.jpg"/>
        <h:outputLabel value="The value of shoppingCart.selectedProduct is: #{shoppingCart.selectedProduct.id}"/>
    </f:view>
</body>
</html>

当我在调试器中运行App时，该值已正确设置为selectedProduct属性，但是该值无法在页面中访问-product.xhtml的输出如下（如果所选产品的ID为4）：

The value of shoppingCart.selectedProduct is:

主页上的产品是从RequestScoped bean的（productController）属性加载的。那么ShoppingCart是一个带有注入productController实例的SessionScoped bean。

package main.java;

import javax.annotation.PostConstruct;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;
import java.io.Serializable;
import java.util.List;

@Named
@SessionScoped
public class ShoppingCart implements Serializable {

    private List<Product> selectedProducts;
    private int numberOfSelectedProducts;
    private Product selectedProduct;

    public Product getSelectedProduct() {
        return selectedProduct;
    }

    public void setSelectedProduct(Product selectedProduct) {
        this.selectedProduct = selectedProduct;
    }

    public List<Product> getSelectedProducts() {
        return selectedProducts;
    }

    public void setSelectedProducts(List<Product> selectedProducts) {
        this.selectedProducts = selectedProducts;
    }

    public int getNumberOfSelectedProducts() {
        return numberOfSelectedProducts;
    }

    public void setNumberOfSelectedProducts(int numberOfSelectedProducts) {
        this.numberOfSelectedProducts = numberOfSelectedProducts;
    }
}

import javax.annotation.PostConstruct;
import javax.faces.view.ViewScoped;
import javax.inject.Inject;
import javax.inject.Named;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

@ViewScoped
@Named
public class ProductController implements Serializable {

    private List<Product> products;
    @Inject
    private ShoppingCart shoppingCart;

    public void setProducts(List<Product> products) {
        this.products = products;
    }

    public ShoppingCart getShoppingCart() {
        return shoppingCart;
    }

    public void setShoppingCart(ShoppingCart shoppingCart) {
        this.shoppingCart = shoppingCart;
    }

    public List<Product> getProducts() {
        return products;
    }

    //v teto metode se pote budou nacitat produkty z DB
    @PostConstruct
    public void loadItems(){
        products = new ArrayList<>();
        products.add(new Product(1, "Nazev1", 11, "Popis1"));
        products.add(new Product(2, "Nazev2", 22, "Popis2"));
        products.add(new Product(3, "Nazev3", 33, "Popis3"));
        products.add(new Product(4, "Nazev4", 44, "Popis4"));
        products.add(new Product(5, "Nazev5", 55, "Popis5"));
        products.add(new Product(6, "Nazev6", 66, "Popis6"));
        products.add(new Product(7, "Nazev7", 77, "Popis7"));
    }

    public Product findById(final int id) {
        List<Product> product = products.stream().filter(p -> p.getId() == id).limit(1).collect(Collectors.toList());
        return product.get(0);
    }
}

package main.java;

import javax.annotation.PostConstruct;
import javax.faces.view.ViewScoped;
import javax.inject.Named;
import java.io.Serializable;

@Named
@ViewScoped
public class Product implements Serializable {
    private int id;
    private String name;
    private double price;
    private String description;

    public Product(int id, String name, double price, String description) {
        this.id = id;
        this.name = name;
        this.price = price;
        this.description = description;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public String getDescription() {
        return description;
    }

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

    @PostConstruct
    public void init(){
        System.out.println("Product created");
    }
}

Answer 1

如果您将f方法添加到 ~~@PostConstruct~~ bean中，如下所示：

@SessionScoped

您会注意到，每个请求实例化bean几次-每个@PostConstruct public void init() { System.out.println("ShoppingCart.init()"); }表达式至少实例化一次。这是因为在CDI环境中使用已弃用的注释#{shoppengCart...}的行为类似于@javax.faces.bean.SessionScoped。

您应该将@NoneScoped用于购物车。

为展示所选产品，我建议添加一个javax.enterprise.context.SessionScoped bean（@ViewScoped，不 ~~javax.faces.view.ViewScoped~~ ）或如果您不使用AJAX，甚至可以使用javax.faces.bean.ViewScoped。（{@RequestScope，不是 ~~javax.enterprise.context.RequestScoped~~ ）。

您使用哪个IDE-它是否没有通知您您使用的sope已过时？

有关更多信息，请参见：How to choose the right bean scope?

除了范围问题之外，您可能还应该使用javax.faces.bean.RequestScoped而不是f:viewParam来将URL查询参数注入bean：

代替：

f:event

执行此操作：

<f:metadata>
    <f:event type="preRenderView" listener="#{shoppingCart.loadSelectedProduct(param.id)}"/>
</f:metadata>

设置bean的属性

1 个答案: