JaxB Xml 找不到 NullPointerException 的原因

如何解决JaxB Xml 找不到 NullPointerException 的原因

我正在尝试使用 java 中的 jaxb 读取 xml 文件，但出于某种原因，在尝试访问产品子元素时，我遇到了 NullpointerException 并且我找不到原因，除非我的代码是不知何故错误，jaxb 没有正确解析 xml 文件中的标签。如果能帮助找出我在这种情况下收到 NullPointer 的原因，我们将不胜感激。

这是错误

Exception in thread "main" java.lang.NullPointerException
    at App.main(App.java:18)

抛出此问题的行在这里。由于某种原因，产品列表基本上是空的。

List<Product> products = order1.getProducts();
            System.out.println(products.size());

从这里

 public static void main(String[] args) {
        Utils utils = new Utils();
        try {
            utils.marshall();
            Orders orders = utils.unMarshal();
            List<Order> order = orders.getOrder();
            Order order1 = order.get(0);
            List<Product> products = order1.getProducts();
            System.out.println(products.size());
            System.out.println(order.size());

        } catch (JAXBException exception) {
            exception.printStackTrace();
        }

现在我的 xml 文件看起来像这样

<?xml version="1.0" encoding="UTF-8"?>
<orders>
    <order created='2012-07-12T15:29:33.000' ID='2343'>
        <product>
            <description>Sony 54.6" (Diag) Xbr Hx929 Internet Tv</description>
            <gtin>00027242816657</gtin>
            <price currency="USD">2999.99</price>
            <supplier>Sony</supplier>
        </product>
        <product>
            <description>Apple iPad 2 with Wi-Fi 16GB - iOS 5 - Black</description>
            <gtin>00885909464517</gtin>
            <price currency="USD">399.0</price>
            <supplier>Apple</supplier>
        </product>
        <product>
            <description>Sony NWZ-E464 8GB E Series Walkman Video MP3 Player Blue</description>
            <gtin>00027242831438</gtin>
            <price currency="USD">91.99</price>
            <supplier>Sony</supplier>
        </product>
    </order>
    <order created='2012-07-13T16:02:22.000' ID='2344'>
        <product>
            <description>Apple MacBook Air A 11.6" Mac OS X v10.7 Lion MacBook</description>
            <gtin>00885909464043</gtin>
            <price currency="USD">1149.0</price>
            <supplier>Apple</supplier>
        </product>
        <product>
            <description>Panasonic TC-L47E50 47" Smart TV Viera E50 Series LED HDTV</description>
            <gtin>00885170076471</gtin>
            <price currency="USD">999.99</price>
            <supplier>Panasonic</supplier>
        </product>
    </order>
</orders>

虽然我使用的类看起来像这样。

package model;


import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import java.util.List;

@XmlRootElement(name = "orders")

public class Orders {

    private List<Order> order;

    public Orders() {
    }

    public Orders(List<Order> order) {
        this.order = order;
    }

    public List<Order> getOrder() {
        return order;
    }

    @XmlElement
    public void setOrder(List<Order> order) {
        this.order = order;
    }
}

@XmlAccessorType(XmlAccessType.FIELD)
public class Order {
    @XmlAttribute(name = "ID")
    private int ID;
    @XmlAttribute
    @XmlJavaTypeAdapter(LocalDateTimeAdapter.class)
    private LocalDateTime created;
    @XmlElementWrapper
    @XmlElement(name = "product")
    private List<Product> products;


    public Order() {
    }

    public Order(int ID,LocalDateTime created,List<Product> products) {
        this.ID = ID;
        this.created = created;
        this.products = products;
    }

    public int getID() {
        return ID;
    }

    public void setID(int ID) {
        this.ID = ID;
    }

    public LocalDateTime getCreated() {
        return created;
    }


    public void setCreated(LocalDateTime created) {
        this.created = created;
    }

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


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

public class Product {
        private String description;
        private long gtin;
        private BigDecimal price;
        private String supplier;

        public Product() {
        }

        public Product(String description,long gtin,BigDecimal price,String supplier) {
            this.description = description;
            this.gtin = gtin;
            this.price = price;
            this.supplier = supplier;
        }

        public String getDescription() {
            return description;
        }

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

        public long getGtin() {
            return gtin;
        }

        @XmlElement
        public void setGtin(long gtin) {
            this.gtin = gtin;
        }

        public BigDecimal getPrice() {
            return price;
        }

        @XmlElement
        public void setPrice(BigDecimal price) {
            this.price = price;
        }

        public String getSupplier() {
            return supplier;
        }

        @XmlElement
        public void setSupplier(String supplier) {
            this.supplier = supplier;
        }
    }

我还为 LocalDateTime 使用了一个适配器。如果需要，我也可以添加它。 谢谢

解决方法

由于您没有为产品列表使用包装元素，因此您需要从 @XmlElementWrapper 类的 products 字段中删除 Order

@XmlElement(name = "product")
private List<Product> products;