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当使用MOXy的元数据与实现java.util.Map的类时，NPE

本文介绍了当使用MOXy的元数据与实现java.util.Map的类时，NPE的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

情况

The situation

我正在使用EclipseLink的MOXy，我正在尝试将外部OX映射XML与实现地图界面但是，每次尝试创建一个JAXBContext时，我会得到以下NPE：

I'm using EclipseLink's MOXy and I'm trying to use the external OX mapping XML with classes that implement the Map interface. However, every time I try create a JAXBContext, I get the following 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)

详细信息

只有当被映射的类实现java.util.Map接口时，才会出现此问题。如果我映射的类不实现该接口，一切都可以正常工作。以下是我试图映射的类的简化示例：

This problem only occurs if the class being mapped implements the java.util.Map interface. If the class I'm mapping does not implement that interface, everything works fine. Here's a simplified example of a class I'm trying to map:

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");
    }
}

以下是MOXy OX元数据的简化示例我想使用：

Here is a simplified sample of the MOXy OX meta data I'd like to use:

<?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>

这是我如何创建我的JAXBContext

Here is how I'm creating my JAXBContext

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);

我使用EclipseLink版本2.3.2，万一这很重要。我也试过版本2.2.1，结果相同。

I'm using EclipseLink version 2.3.2, in case that's important. I've also tried with version 2.2.1 with the same results.

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，如果我缺少一些基本的东西，我很好奇。我不希望OX映射使用地图的名称/值对，而是添加到类中的自定义getter和setter。

This the first time I've tried to use JAXB on a class that implements the java.util.Map interface and I'm curious if I'm missing something fundamental. I don't expect the OX Mappings to work with the Map's name/value pairs, but instead with the custom getters and setters added to the class.

是一个配置，如这应该工作？

Is a configuration like this supposed to work?

其他详细信息


  1. 示例代码中使用的DelegatedMap不会扩展 java.util.HashMap，它只包含一个实例，并实现Map接口。此外，该类用@XmlAccessorType（XmlAccessType.NONE）注释。

  2. 无论使用哪个抽象类，我使用了SampleClassA，都会得到相同的错误。如果SampleClassA扩展了一个不实现地图的类，那么所有的行为都是正确的。

  3. 我正在使用的代码库需要许多类来实现Map接口。
  1. The DelegatedMap used in the sample code does not extend java.util.HashMap, it just wraps an instance of one and implements the Map interface. Also, that class is annotated with @XmlAccessorType(XmlAccessType.NONE).
  2. I get the same error regardless of which abstract class that implements the Map interface I use for SampleClassA. If SampleClassA extends a class that does not implement a map, everything behaves correctly.
  3. The code base I'm working with requires many of the classes to implement the Map interface.


推荐答案

注意：我是，并且是专家组

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

这是一个非常有趣的用例。 JAXB（JSR-222）具有映射和域对象的表示形式，因此它可以考虑混合对象的行为方式。我添加了以下增强请求来介绍它的支持：

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:



  • http://bugs.eclipse.org/37640

更新

我们刚刚完成了此增强功能。您可以从2012年4月19日起使用EclipseLink 2.4.0每晚下载开始尝试使用：

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:



  • http://www.eclipse.org/eclipselink/downloads/nightly.php

修复涉及利用超类型属性来指定超类型以覆盖真实超级型。 超级类型属性之前仅被我们的

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

以下是您的问题中描述的 DelegatatedMap 类的实现。

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

要指定MOXy作为您的JAXB提供程序，您需要在...中添加一个名为 jaxb.properties 的文件与您的域类相同的包含以下条目：

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

演示 

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);
    }

}

输出 

Foo
Foo
<?xml version="1.0" encoding="UTF-8"?>
<SAMPLE SomeProperty="Foo"/>

这篇关于当使用MOXy的元数据与实现java.util.Map的类时，NPE的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

10-26 22:12
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