java - 如何在 JAXB 中将对象作为 @XmlValue 嵌入？

Question

我想表示 List<Map<String,Object>> 的一个实例在 XML 中如下所示:

<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>

哪里key1和 key2是字符串，key3为零，keyDate是一个日期。

我可以使用以下 XmlAdapter 的实现接近 :

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>();
    }
}

和下面的测试代码:

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>

我真正想要的是放弃嵌套的 value条目内的标记。我天真的假设是我可以替换 @XmlElement关于 value 的注释至 @XmlValue .然而，这导致 JAXB 吐了一地:

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的 XmlAdapter 来做到这一点-based 代码，但我想我已经盯着这个看太久了，想不出来!

Answer 1

奇怪。如果您将 map 类型从 <String, Object> 更改为至 <String, String>它按预期工作。

更新:似乎如果您强制 JAXB 使用@XmlValue(或@XmlAttribute)呈现值，它就没有地方放置其类型信息:xsi:type="xs:dateTime" ...它需要是一个@XmlElement

我的建议是使用 Map<String, String>使用从 String 编码/解码的适配器至 Object取决于底层类型:

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();
    }
}