使用JAXB编组/解组Java超类和子类

Question

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以创建一个类似于以下内容的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：说我有一个Car，Van和Bicycle对象，它们是Vehicle的子类。我是否可以操纵我的JAXB类来编写一个会产生类似结果的XML文件？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;
    }
}

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类

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());
        }
    }
}

清单类别

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;
    }
}

Answer 1

谢谢各位的意见。我使用了所有答案的反馈，但最终都是有效的结合了这就是为什么我为将来可能遇到此问题的任何人创建单独的答案。

为了使它起作用，我必须确保在marhsalled /
unmarshalled的super和sub类中的所有getter方法都用标注@XmlElement。这将确定相应变量的XML标签。

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

必须对超类进行注释，@XmlSeeAlso以将子类绑定到它。即在我的代码中RoadVehicle是超类，并且Car和Van类都对其进行了扩展。

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

现在使用超级类和子类进行注释，唯一需要注释的其他类是列表类（在我的代码中为车库）。此处的更改将确定填充了哪些XML标签。

通过将@XmlRootElement注释应用于类的顶部来设置XML根标签。即“车辆”将是我的示例中的根XML标签。

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

最后，@XmlElements必须@XmlElements为每个需要XML标签的子类声明一个带有注释的列表，并name提供XML标签的名称。必须在该集合的getter方法上方声明此列表。

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