如何在JAXB中将Object作为@XmlValue嵌入？

Question

我想在XML中表示List<Map<String,Object>>的实例，如下所示：

<row>
   <entry key="key1" xsi:type="xs:string" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">value1</entry>
   <entry key="key2" xsi:type="xs:string" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">value2</entry>
   <entry key="key3" />
   <entry key="keyDate" xsi:type="xs:dateTime" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2012-08-19T13:00:59.412-04:00</entry>
</row>

其中key1和key2为字符串，key3为零，keyDate为日期。

我可以使用XmlAdapter的以下实现关闭：

package net.parkerson.test1;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class JAXBMapAdapter extends XmlAdapter<JAXBMapAdapter.JAXBMap, Map<String, Object>>
{

    @Override
    public JAXBMap marshal(Map<String, Object> map) throws Exception
    {
        JAXBMap jaxbMap = new JAXBMap();
        for (Entry<String, Object> entry : map.entrySet())
        {
            jaxbMap.entry.add(new JAXBMapEntry(entry));
        }
        return jaxbMap;

    }

    @Override
    public Map<String, Object> unmarshal(JAXBMapAdapter.JAXBMap mappedObject) throws Exception
    {
        HashMap<String, Object> map = new HashMap<String, Object>();
        for (JAXBMapEntry entry : mappedObject.entry)
        {
            map.put(entry.key, entry.value);
        }
        return map;
    }

    public static class JAXBMapEntry
    {

        @XmlAttribute
        public String key;

        @XmlElement
        public Object value;

        public JAXBMapEntry()
        {
        }

        public JAXBMapEntry(Map.Entry<String, Object> entry)
        {
            key = entry.getKey();
            value = entry.getValue();
        }
    }

    public static class JAXBMap
    {
        public List<JAXBMapAdapter.JAXBMapEntry> entry = new ArrayList<JAXBMapAdapter.JAXBMapEntry>();
    }
}

以及以下测试代码：

package net.parkerson.test1;

import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.xml.bind.JAXB;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElements;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

import net.parkerson.test1.JAXBMapAdapter;

public class Test1
{
    @XmlRootElement
    public static class Thingy
    {
        @XmlElements(@XmlElement(name = "row"))
        @XmlJavaTypeAdapter(type=Map.class, value=JAXBMapAdapter.class)
        public List<Map<String,Object>> rows;
    }

    public static void main(String[] args) throws Exception
    {
        Test1.Thingy thingy = new Test1.Thingy();

        Map<String,Object> thing1 = new HashMap<String,Object>();
        thing1.put("foo", "bar");
        thing1.put("date", new Date());

        Map<String,Object> thing2 = new HashMap<String,Object>();
        thing2.put("foo", "baz");
        thing2.put("date", new Date());

        List<Map<String,Object>> things = new ArrayList<Map<String,Object>>();
        things.add(thing1);
        things.add(thing2);

        thingy.rows = things;

        java.io.StringWriter sw = new java.io.StringWriter();
        JAXB.marshal(thingy, sw);
        System.out.print(sw.toString());
    }

}

生成这个：

<thingy>
    <row>
        <entry key="foo">
            <value xsi:type="xs:string" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">bar</value>
        </entry>
        <entry key="date">
            <value xsi:type="xs:dateTime" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2012-08-19T13:20:57.484-04:00</value>
        </entry>
    </row>
    <row>
        <entry key="foo">
            <value xsi:type="xs:string" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">baz</value>
        </entry>
        <entry key="date">
            <value xsi:type="xs:dateTime" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2012-08-19T13:20:57.484-04:00</value>
        </entry>
    </row>
</thingy>

我真正想要的是抛弃条目中嵌套的value标签。我天真的假设是我可以将@XmlElement上的value注释替换为@XmlValue。然而，这导致JAXB在整个地板上呕吐：

Exception in thread "main" java.lang.NullPointerException
    at com.sun.xml.internal.bind.v2.runtime.reflect.TransducedAccessor.get(TransducedAccessor.java:154)
    at com.sun.xml.internal.bind.v2.runtime.property.ValueProperty.<init>(ValueProperty.java:66)
    at com.sun.xml.internal.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:95)
    at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:145)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:479)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:498)
    at com.sun.xml.internal.bind.v2.runtime.property.ArrayElementProperty.<init>(ArrayElementProperty.java:97)
    at com.sun.xml.internal.bind.v2.runtime.property.ArrayElementNodeProperty.<init>(ArrayElementNodeProperty.java:47)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.sun.xml.internal.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:113)
    at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:145)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:479)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:498)
    at com.sun.xml.internal.bind.v2.runtime.property.ArrayElementProperty.<init>(ArrayElementProperty.java:97)
    at com.sun.xml.internal.bind.v2.runtime.property.ArrayElementNodeProperty.<init>(ArrayElementNodeProperty.java:47)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.sun.xml.internal.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:113)
    at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:145)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:479)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:305)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1100)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:143)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:110)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:202)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:376)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:574)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:522)
    at javax.xml.bind.JAXB$Cache.<init>(JAXB.java:87)
    at javax.xml.bind.JAXB.getContext(JAXB.java:114)
    at javax.xml.bind.JAXB._marshal(JAXB.java:538)
    at javax.xml.bind.JAXB.marshal(JAXB.java:431)
    at net.parkerson.test1.Test1.main(Test1.java:49)

我确信有一种方法可以使用我基于XmlAdapter的代码来实现这一点，但我想我已经盯着它看了太长时间才想出来！

Answer 1

奇怪。如果您将地图类型从<String, Object>更改为<String, String>，则可以按预期工作。

更新： 似乎如果强制JAXB使用@XmlValue（或@XmlAttribute）呈现值，则无法放置其类型信息：xsi:type="xs:dateTime" ...它必须是@XmlElement

我的建议是使用Map<String, String>与String到Object编码/解码的适配器，具体取决于基础类型：

public class MySmartAdapter extends XmlAdapter<String, Object> {
    @Override
    public Object unmarshal(String s) throws Exception {
        //check if s is date and return date
        //check for other types
        return s;
    }

    @Override
    public String marshal(Object o) throws Exception {
        return o != null ? o.toString() : null;
    }
}


public static class JAXBMapEntry
{

    @XmlAttribute
    public String key;

    @XmlValue
    @XmlJavaTypeAdapter(MySmartAdapter.class)
    public Object value;

    public JAXBMapEntry()
    {
    }

    public JAXBMapEntry(Map.Entry<String, Object> entry)
    {
        key = entry.getKey();
        value = entry.getValue();
    }
}