将多态对象的集合配置为在JAXB2中工作

Question

我正在从Castor切换到JAXB2以在XML和Java对象之间执行封送/解组。我在尝试配置多态对象集合时遇到了问题。

示例XML

<project name="test project"> 
    <orange name="fruit orange" orangeKey="100" /> 
    <apple name="fruit apple" appleKey="200" /> 
    <orange name="fruit orange again" orangeKey="500" /> 
</project> 

工程类

的oranges表工作正常，我看到列表中的2个橘子。但是，我不知道如何配置fruitList。 fruitList应该有3个水果：2个橙子和1个苹果。

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public class Project { 

    @XmlAttribute 
    private String   name; 

    @XmlElement(name = "orange") 
    private List<Orange> oranges  = new ArrayList<Orange>(); 

    // Not sure how to configure this... help! 
    private List<Fruit>  fruitList = new ArrayList<Fruit>(); 
} 

水果类

果是一个抽象类。出于某种原因，将这个类定义为抽象似乎导致了很多问题。

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public abstract class Fruit { 

    @XmlAttribute 
    private String name; 
} 

橙类

public class Orange extends Fruit { 

    @XmlAttribute 
    private String orangeKey; 
} 

苹果类

public class Apple extends Fruit { 

    @XmlAttribute 
    private String appleKey; 
} 

如何将我的fruitList在Project配置达到我想要的吗？

非常感谢！

Answer 1

你想利用@XmlElementRef这相当于取代基的XML架构的概念，它对应于你的问题。

第1步 - 使用@XmlElementRef

的fruitList属性标注有@XmlElementRef：

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.XmlAttribute; 
import javax.xml.bind.annotation.XmlElementRef; 
import javax.xml.bind.annotation.XmlRootElement; 

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public class Project { 

    @XmlAttribute 
    private String name; 

    @XmlElementRef 
    private List<Fruit> fruitList = new ArrayList<Fruit>(); 

} 

第2步 - 注释苹果与橘子同@XmlRootElement

import javax.xml.bind.annotation.XmlAccessType; 
import javax.xml.bind.annotation.XmlAccessorType; 
import javax.xml.bind.annotation.XmlAttribute; 
import javax.xml.bind.annotation.XmlRootElement; 

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public class Apple extends Fruit { 

    @XmlAttribute 
    private String appleKey; 

} 

和

import javax.xml.bind.annotation.XmlAccessType; 
import javax.xml.bind.annotation.XmlAccessorType; 
import javax.xml.bind.annotation.XmlAttribute; 
import javax.xml.bind.annotation.XmlRootElement; 

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public class Orange extends Fruit { 

    @XmlAttribute 
    private String orangeKey; 

} 

演示代码

以下代码可被用于证明溶液：

import java.io.File; 

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

public class Demo { 

    public static void main(String[] args) throws Exception { 
     JAXBContext jc = JAXBContext.newInstance(Project.class, Apple.class, Orange.class); 

     Unmarshaller unmarshaller = jc.createUnmarshaller(); 
     Project project = (Project) unmarshaller.unmarshal(new File("input.xml")); 

     Marshaller marshaller = jc.createMarshaller(); 
     marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); 
     marshaller.marshal(project, System.out); 
    } 

} 

更多信息：

• http://bdoughan.blogspot.com/2010/11/jaxb-and-inheritance-using-substitution.html

Answer 2

认沽XmlAnyElement将注释：

@XmlAnyElement(lax = true) 
private List<Fruit>  fruitList = new ArrayList<Fruit>(); 

Answer 3

把玩后，周围......我想我现在的工作： -

@XmlRootElement 
@XmlAccessorType(XmlAccessType.FIELD) 
public class Project { 

    @XmlAttribute 
    private String  name; 

    // this has to be commented out, or else oranges won't show up in fruitList 
    // @XmlElement(name = "orange") 
    // private List<Orange> oranges = new ArrayList<Orange>(); 

    @XmlElements({ 
      @XmlElement(name = "orange", type = Orange.class), 
      @XmlElement(name = "apple", type = Apple.class) 
    }) 
    private List<Fruit> fruitList = new ArrayList<Fruit>(); 

}