使用 JAXB 编组/解组 Java 超类和子类

我一直在尝试 JAXB 教程，并设法使代码能够从 Java 对象生成 XML 文件，然后能够使用 XML 生成 Java 对象。目前，它读取同一类的多个实例来创建一个类似于以下文件的 XML 文件

<Car>
    <regplate>TR54</regplate>
    <colour>red</colour>
    <energyrating>5</energyrating>
</Car>
<Car>
    <regplate>BN04 THY</regplate>
    <colour>yellow</colour>
    <energyrating>3</energyrating>
</Car>
<Car>
    <regplate>BN05 THY</regplate>
    <colour>yellow</colour>
    <energyrating>5</energyrating>
</Car>

我希望能够使用 JAXB 技术来处理子类。例如：假设我有一个 Car、Van 和 Bicycle 对象，它们是 Vehicle 的子类。我是否可以操作 JAXB 类来编写一个 XML 文件来生成与此类似的内容？我在下面提供了我正在使用的代码。

<Vehicle>
    <Car>
        <regplate>TR54</regplate>
        <colour>red</colour>
        <energyrating>5</energyrating>
    </Car>
    <Van>
        <regplate>MN05 RFD</regplate>
        <colour>red</colour>
        <energyrating>5</energyrating>
    </Van>
    <Car>
        <regplate>ZX54 UJK</regplate>
        <colour>red</colour>
        <energyrating>1</energyrating>
    </Car>
</Vehicle>

主班

package basictransport2;

public class Main
{
    public static void main(String[] args)
    {
        JAXB parser = new JAXB();
        parser.marshall();
        //parser.unmarshallList();
    }
}

车辆类别

package basictransport2;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

//@XmlRootElement(name = "Vehicle")
public class Vehicle
{
    private int ownerId;

    public Vehicle(int ownerId)
    {
        this.setOwnerId(ownerId);
    }

    //@XmlElement (name = "Owner ID")
    public int getOwnerId()
    {
        return ownerId;
    }

    public void setOwnerId(int ownerId)
    {
        this.ownerId = ownerId;
    }


    public int getEnergyRating()
    {
        return (Integer) null;
    }


    public String getColour()
    {
        return null;
    }

    public String getRegPlate()
    {
        return null;
    }
}

汽车类

package basictransport2;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

//@XmlRootElement(name = "Car")
public class Car extends Vehicle
{
    private String regPlate;
    private int energyRating;
    private String colour;

    public Car(String regPlate, int energyRating, String colour, int ownerId)
    {
        super(ownerId);
        this.regPlate = regPlate;
        this.energyRating = energyRating;
        this.colour = colour;
    } 

    public Car(int ownerId)
    {
        super(ownerId);
    }

    //@XmlElement (name = "Registration")
    public String getRegPlate()
    {
        return regPlate;
    }

    public void setRegPlate(String regPlate)
    {
        if(this.regPlate == null)
        {
            this.regPlate = regPlate;
        }
    }

    //@XmlElement (name = "Energy Rating")
    public int getEnergyRating()
    {
        return energyRating;
    }

    public void setEnergyRating(int energyRating)
    {
        this.energyRating = energyRating;
    }

    //@XmlElement (name = "Colour")
    public String getColour()
    {
        return colour;
    }

    public void setColour(String colour)
    {
        this.colour = colour;
    }
}

JAXB级

package basictransport2;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class JAXB
{   
    public void marshall()
    {
        try
        {
            List<Vehicle> vehicleList = new ArrayList<Vehicle>();

            vehicleList.add(new Car("SG09 TYH", 4, "Yellow", 1));
            vehicleList.add(new Car("XX09 VVV", 3, "Red", 2));
            vehicleList.add(new Car("BL09 TYZ", 4, "Blue", 3));

            Garage listOfVehicles = new Garage();
            listOfVehicles.setListOfVehicles(vehicleList);

            JAXBContext context = JAXBContext.newInstance(Garage.class);
            Marshaller marshaller = context.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
            marshaller.marshal(listOfVehicles, System.out);
            marshaller.marshal(listOfVehicles, new File("src\\data\\listcar.xml"));
        }

        catch(Exception e)
        {
            System.out.println(e.getMessage());
        }
    }

    public void unmarshall()
    {
        try
        {
            JAXBContext context = JAXBContext.newInstance(Garage.class);
            Unmarshaller unmarhsaller = context.createUnmarshaller();
            Garage listOfVehicles = (Garage)unmarhsaller.unmarshal(new File("src\\data\\listcar.xml"));
            System.out.println("List Car information");

            for(Vehicle vehicle : listOfVehicles.getListOfVehicles())
            {
                System.out.println("Reg Plate: " + vehicle.getRegPlate());
                System.out.println("Energy Rating: " + vehicle.getEnergyRating());
                System.out.println("Colour: " + vehicle.getColour());
                System.out.println("================");
            }    
        }

        catch (Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
}

列表类

package basictransport2;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElements;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlSeeAlso;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name="Vehicle")
public class Garage
{
    @XmlElements
    ({
        @XmlElement(name = "Car", type = Car.class, required = false)
    })    

    private List<Vehicle> vehicleCollection = new ArrayList<Vehicle>();

    public List<Vehicle> getListOfVehicles()
    {
        return vehicleCollection;
    }

    public void setListOfVehicles(List<Vehicle> listOfVehicles)
    {
        this.vehicleCollection = listOfVehicles;
    }
}

谢谢各位的意见。我使用了您所有答案的反馈，但最终它们的组合起作用了，这就是为什么我为将来可能遇到此问题的任何人创建了一个单独的答案。

为了让它工作，我必须确保正在编组/解组的超类和子类中的所有 getter 方法都用注释@XmlElement。这将确定相应变量的 XML 标记。

@XmlElement (name = "OwnerID")
    public int getOwnerId()
    {
        return ownerId;
    }

超类必须注释为@XmlSeeAlso将子类绑定到它。即在我的代码中RoadVehicle是超类，并且都是Car and Van课程扩展了它。

@XmlSeeAlso({Car.class, Van.class})
public class Vehicle
{

现在，超级类和子类都已注释，唯一需要注释的其他类是列表类（我的代码中的 Garage）。此处的更改将确定 XML 标记的填充内容。

根 XML 标记是通过应用@XmlRootElement注释到类的顶部。即“Vehicle”将是我的示例中的根 XML 标记。

@XmlRootElement(name = "Vehicle")
public class Garage
{

最后一个@XmlElements清单必须以@XmlElements每个需要 XML 标记的子类的注释name提供 XML 标记的名称。该列表必须在集合的 getter 方法之上声明。

@XmlElements
    ({
        @XmlElement(name = "Car", type = Car.class, required = false),
        @XmlElement(name = "Van", type = Van.class, required = false)
    })    
    public List<Vehicle> getListOfVehicles()
    {
        return vehicleCollection;
    }