问题描述
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;