我一直在使用jaxb获取一个包含客户列表的xml文件，以便将其转换为java中可用的pojo。在完成本教程之后，我在尝试加载客户列表时遇到了一个空指针异常。我一直在打印什么方法可以达到，它似乎从来没有呼吁 setCustomers(...) {...} 功能。以下是xml的格式：

<Customers>
    <Customer>
      <Age>86</Age>
      <CustomerId>101</CustomerId>
      <Email>R_Heimbach@gmail.net</Email>
      <Name>Robert Heimbach</Name>
      <Orders>
        <Order>
          <CustomerId>101</CustomerId>
          <Lines>
            <OrderLine>
              <OrderLineId>299</OrderLineId>
              <Price>12</Price>
              <ProductId>1785</ProductId>
              <Qty>1</Qty>
              <Total>12</Total>
            </OrderLine>
          </Lines>
          <OrderId>148</OrderId>
          <Total>12</Total>
        </Order>
        <Order>
          <CustomerId>101</CustomerId>
          <Lines>
            <OrderLine>
              <OrderLineId>300</OrderLineId>
              <Price>51</Price>
              <ProductId>8107</ProductId>
              <Qty>2</Qty>
              <Total>102</Total>
            </OrderLine>
          </Lines>
          <OrderId>149</OrderId>
          <Total>102</Total>
        </Order>
      </Orders>
    </Customer>
    <Customer>
      <Age>63</Age>
      <CustomerId>102</CustomerId>
      <Email>B_Smith@gmail.net</Email>
      <Name>Bob Smith</Name>
      <Orders>
        <Order>
          <CustomerId>102</CustomerId>
          <Lines>
            <OrderLine>
              <OrderLineId>300</OrderLineId>
              <Price>12</Price>
              <ProductId>1785</ProductId>
              <Qty>1</Qty>
              <Total>12</Total>
            </OrderLine>
          </Lines>
          <OrderId>149</OrderId>
          <Total>12</Total>
        </Order>
        <Order>
          <CustomerId>102</CustomerId>
          <Lines>
            <OrderLine>
              <OrderLineId>301</OrderLineId>
              <Price>51</Price>
              <ProductId>8107</ProductId>
              <Qty>2</Qty>
              <Total>102</Total>
            </OrderLine>
          </Lines>
          <OrderId>149</OrderId>
          <Total>102</Total>
        </Order>
      </Orders>
    </Customer>

我的客户.java：

@XmlRootElement(name = "Customers")
@XmlAccessorType(XmlAccessType.FIELD)
public class Customers {

    @XmlElement(name = "Customer")
    private List<Customer> customers = null;

    public List<Customer> getCustomers() {
        return customers;
    }

    public void setCustomers(List<Customer> customers) {
        for(Customer customer : customers) {
            System.out.println(customer.getName());
        }
        this.customers = customers;
    }

}

我的客户.java：

@XmlRootElement(name = "Customer")
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {

    @XmlElement(name = "CustomerId")
    private int customerId;

    @XmlElement(name = "Age")
    private int age;

    @XmlElement(name = "Email")
    private String email;

    @XmlElement(name = "Name")
    private String name;

    @XmlElement(name = "Orders")
    private List<Order> orders = null;

    public int getCustomerId() {
        return customerId;
    }

    public void setCustomerId(int customerId) {
        this.customerId = customerId;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

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

    public List<Order> getOrders() {
        return orders;
    }

    public void setOrders(List<Order> orders) {
        this.orders = orders;
    }

}

我的订单.java：

@XmlRootElement(name = "Order")
@XmlAccessorType(XmlAccessType.FIELD)
public class Order {

    @XmlElement(name = "OrderId")
    private int orderId;

    @XmlElement(name = "CustomerId")
    private int customerId;

    @XmlElement(name = "Total")
    private int total;

    @XmlElement(name = "Lines")
    private List<OrderLine> lines = null;

    public int getOrderId() {
        return orderId;
    }

    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }

    public int getCustomerId() {
        return customerId;
    }

    public void setCustomerId(int customerId) {
        this.customerId = customerId;
    }

    public int getTotal() {
        return total;
    }

    public List<OrderLine> getLines() {
        return lines;
    }

    public void setLines(List<OrderLine> lines) {
        this.lines = lines;
    }

    public void setTotal(int total) {
        this.total = total;
    }

}

my orderline.java:

@XmlRootElement(name = "OrderLine")
@XmlAccessorType(XmlAccessType.FIELD)
public class OrderLine {

    @XmlElement(name = "OrderLineId")
    private int orderLineId;

    @XmlElement(name = "Price")
    private int price;

    @XmlElement(name = "ProductId")
    private int productId;

    @XmlElement(name = "Qty")
    private int qty;

    @XmlElement(name = "Total")
    private int total;

    public int getOrderLineId() {
        return orderLineId;
    }

    public void setOrderLineId(int orderLineId) {
        this.orderLineId = orderLineId;
    }

    public int getPrice() {
        return price;
    }

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

    public int getProductId() {
        return productId;
    }

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

    public int getQty() {
        return qty;
    }

    public void setQty(int qty) {
        this.qty = qty;
    }

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

}

主要功能：

public static void main(String[] args) {
        try {

            File file = new File("customers.xml");
            JAXBContext jaxbContext = JAXBContext.newInstance(Customers.class);

            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

            Customers customers = (Customers) jaxbUnmarshaller.unmarshal(file);

            System.out.println(customers.getCustomers().size());

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

我觉得我的注解有点混乱。是什么导致了 System.out.println(customers.getCustomers().size()); 在运行时导致nullpointerexception？它似乎解析了所有的内容，但没有在pojo中分配任何内容。