4

情况

我正在使用 EclipseLink 的 MOXy，并且正在尝试将外部 OX 映射 XML 与实现 Map 接口的类一起使用。但是，每次我尝试创建 JAXBContext 时，都会得到以下 NPE：

Caused by: javax.xml.bind.JAXBException
 - with linked exception:
[java.lang.NullPointerException]
    at org.eclipse.persistence.jaxb.JAXBContext$TypeMappingInfoInput.createContextState(JAXBContext.java:832)
    at org.eclipse.persistence.jaxb.JAXBContext.<init>(JAXBContext.java:143)
    at org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(JAXBContextFactory.java:142)
    at org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(JAXBContextFactory.java:129)
    at org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(JAXBContextFactory.java:93)
    at org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(JAXBContextFactory.java:83)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:210)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:336)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:574)
    at com.example.MOXyOXTest<clinit>(MOXyOXTest.java:59)
Caused by: java.lang.NullPointerException
    at org.eclipse.persistence.jaxb.compiler.XMLProcessor.processXML(XMLProcessor.java:202)
    at org.eclipse.persistence.jaxb.compiler.Generator.<init>(Generator.java:145)
    at org.eclipse.persistence.jaxb.JAXBContext$TypeMappingInfoInput.createContextState(JAXBContext.java:829)

细节

仅当被映射的类实现 java.util.Map 接口时，才会出现此问题。如果我正在映射的类没有实现该接口，那么一切正常。这是我要映射的类的简化示例：

package com.example;

import java.util.Map;

// This class just wraps a java.util.HashMap
import com.xetus.lib.type.DelegatedMap;

public class SampleClassA extends DelegatedMap<String, Object>{

    public SampleClassA(){
        super();
    }

    public SampleClassA(Map<String, Object> m){
        super(m);
    }

    public void setSomeProperty(String value){
        put("somevalue", value);
    }

    public String getSomeProperty(){
        return (String) get("somevalue");
    }
}

这是我想使用的 MOXy OX 元数据的简化示例：

<?xml version="1.0"?>
<xml-bindings
  xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
  package-name="com.example"
  xml-mapping-metadata-complete="true"> 
  <java-types>
  <java-type name="SampleClassA" xml-accessor-type="NONE">
   <xml-root-element name="SAMPLE" />
    <java-attributes>
     <xml-attribute type="java.lang.String" name="SomeProperty" required="true">
     <xml-access-methods get-method="getSomeProperty" set-method="setSomeProperty"/>
    </xml-attribute>
   </java-attributes>
  </java-type>
 </java-types>
</xml-bindings>

这是我创建 JAXBContext 的方式

Map<String, Object> props = new HashMap<String, Object>(1);
List bindings = new ArrayList(1);
bindings.add(new StreamSource(MOXyOXTest.class.getResourceAsStream("test-mappings.xml")));
props.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, bindings);

cntxt = JAXBContext.newInstance(new Class[] { SampleClassA.class }, props);

我正在使用 EclipseLink 2.3.2 版，以防万一。我也尝试过使用 2.2.1 版，结果相同。

我的问题

这是我第一次尝试在实现 java.util.Map 接口的类上使用 JAXB，我很好奇我是否遗漏了一些基本的东西。我不希望 OX 映射与 Map 的名称/值对一起使用，而是与添加到类中的自定义 getter 和 setter 一起使用。

这样的配置应该工作吗？

额外细节

  1. 示例代码中使用的 DelegatedMap 没有扩展java.util.HashMap，它只是包装了一个实例并实现了 Map 接口。此外，该类使用@XmlAccessorType(XmlAccessType.NONE) 进行注释。
  2. 无论哪个抽象类实现了我用于 SampleClassA 的 Map 接口，我都会遇到相同的错误。如果 SampleClassA 扩展了一个未实现映射的类，则一切正常。
  3. 我正在使用的代码库需要许多类来实现 Map 接口。
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1 回答 1

2

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

This is a very interesting use case. JAXB (JSR-222) has representations for maps and domain objects, so it is intersting to consider how a hybrid object should behave. I have added the following enhancement request to introduce support for it:

UPDATE

We have just finished implementing this enhancement. You can try it out using an EclipseLink 2.4.0 nightly download start on April 19, 2012 from the following location:

The fix involves leveraging the super-type property to specify a super type to override the real super type. The super-type property was previously only leveraged by our dynamic JAXB support.

bindings.xml

<?xml version="1.0"?>
<xml-bindings 
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10075634">
    <java-types>
        <java-type name="SampleClassA" super-type="java.lang.Object" xml-accessor-type="NONE">
            <xml-root-element name="SAMPLE" />
            <java-attributes>
                <xml-attribute java-attribute="someProperty" name="SomeProperty" required="true"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

DelegatedMap

Below is an implementation of the DelegatatedMap class as described in your question.

package forum10075634;

import java.util.*;

public class DelegatedMap<K,V> implements Map<K,V> {

    private Map<K,V> map;

    public DelegatedMap() {
        map = new HashMap<K,V>();
    }

    public DelegatedMap(Map<K,V> map) {
        this.map = map;
    }

    public void clear() {
        map.clear();
    }

    public boolean containsKey(Object key) {
        return map.containsKey(key);
    }

    public boolean containsValue(Object value) {
        return map.containsValue(value);
    }

    public Set<java.util.Map.Entry<K, V>> entrySet() {
        return map.entrySet();
    }

    public V get(Object key) {
        return map.get(key);
    }

    public boolean isEmpty() {
        return map.isEmpty();
    }

    public Set<K> keySet() {
        return map.keySet();
    }

    public V put(K key, V value) {
        return map.put(key, value);
    }

    public void putAll(Map<? extends K, ? extends V> m) {
        map.putAll(m);
    }

    public V remove(Object key) {
        return map.remove(key);
    }

    public int size() {
        return map.size();
    }

    public Collection<V> values() {
        return map.values();
    }

}

SampleClassA

package forum10075634;

import java.util.Map;

public class SampleClassA extends DelegatedMap<String, Object> {

    public SampleClassA() {
        super();
    }

    public SampleClassA(Map<String, Object> m) {
        super(m);
    }

    public void setSomeProperty(String value) {
        put("somevalue", value);
    }

    public String getSomeProperty() {
        return (String) get("somevalue");
    }

}

jaxb.properties

To specify MOXy as your JAXB provider you need to add a file called jaxb.properties in the same package as your domain classes with the following entry:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

Demo

package forum10075634;

import java.io.StringReader;
import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(1);
        properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, "forum10075634/bindings.xml");
        JAXBContext jc = JAXBContext.newInstance(new Class[] {SampleClassA.class}, properties);

        StringReader xml = new StringReader("<SAMPLE SomeProperty='Foo'/>");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        SampleClassA sampleClassA = (SampleClassA) unmarshaller.unmarshal(xml);

        System.out.println(sampleClassA.getSomeProperty());
        System.out.println(sampleClassA.get("somevalue"));

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

}

Output

Foo
Foo
<?xml version="1.0" encoding="UTF-8"?>
<SAMPLE SomeProperty="Foo"/>
于 2012-04-10T15:20:45.413 回答