爲什麼MOXY JAXB編組爲空字符串，而JAXB參考實現不是？

下面顯示的JUnit測試在MOXy中失敗（在我的環境中），但適用於JAXB參考實現。爲什麼MOXY JAXB編組爲空字符串，而JAXB參考實現不是？

預期產生的XML是：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> 
<itemManager> 
    <items> 
     <value>2</value> 
    </items> 
</itemManager>

但MOXY接通 - 包含jaxb.properties：

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

生成的XML字符串是空的。

什麼可能是這種行爲的原因，以及需要做些什麼來解決它？

我試過EclipseLink MOXy版本2.5.1和2.4.2 - 請參閱下面的pom.xml片段。依賴關係是pom.xml中的第一個，其次是許多其他（這也可能會損壞節目）。 JUnit測試的

<!-- Eclipselink moxy --> 
<dependency> 
    <groupId>org.eclipse.persistence</groupId> 
    <artifactId>org.eclipse.persistence.moxy</artifactId> 
    <version>2.4.2</version> 
    <!-- <version>2.5.1</version> --> 
    <scope>test</scope> 
</dependency>

Java代碼：

package com.bitplan.storage.moxy; 

import static org.junit.Assert.*; 

import java.io.StringWriter; 
import java.util.ArrayList; 
import java.util.Collection; 
import java.util.Iterator; 
import java.util.List; 

import javax.xml.bind.JAXBContext; 
import javax.xml.bind.Marshaller; 
import javax.xml.bind.annotation.XmlAccessType; 
import javax.xml.bind.annotation.XmlAccessorType; 
import javax.xml.bind.annotation.XmlElement; 
import javax.xml.bind.annotation.XmlRootElement; 
import javax.xml.bind.annotation.XmlTransient; 

import org.junit.Test; 

/** 
* show problem with empty xml result for Jaxb Marshaller 
* 
* @author wf 
* 
*/ 
public class TestEmptyXml { 

    public interface Copyable<T> { 
     /** 
     * copy me from the copyable 
     * 
     * @param othe 
     *   - the source copyaqble to copy from 
     */ 
     public void copyFrom(T other); 
    } 

    public interface BO<BO_T> extends Copyable<BO_T> { 

    } 

    public interface ItemInterface { 

    } 

    @XmlRootElement 
    public static class Item implements ItemInterface { 
     int value; 

     /** 
     * @return the value 
     */ 
     public int getValue() { 
      return value; 
     } 

     /** 
     * @param value 
     *   the value to set 
     */ 
     public void setValue(int value) { 
      this.value = value; 
     } 

     public Item() { 

     } 

     public Item(int pValue) { 
      value = pValue; 
     } 

    } 

    public interface ItemManagerInterface { 
     public void setItems(List<Item> pItems); 

     public List<Item> getItems(); 
    } 

    public interface MoxyList<BO_T> extends Collection<BO_T> { 

    } 

    public interface MoxyManager<BO_T> extends MoxyList<BO_T> { 
    } 

    public static class MoxyManagerImpl<BO_T> implements MoxyManager<BO_T> { 
     public transient List<BO_T> bolist = new ArrayList<BO_T>(); 

     @Override 
     public boolean add(BO_T arg0) { 
      boolean result = bolist.add(arg0); 
      return result; 
     } 

     @Override 
     public boolean addAll(Collection<? extends BO_T> arg0) { 
      boolean result = bolist.addAll(arg0); 
      return result; 
     } 

     @Override 
     public void clear() { 
      bolist.clear(); 
     } 

     @Override 
     public boolean contains(Object arg0) { 
      boolean result = bolist.contains(arg0); 
      return result; 
     } 

     @Override 
     public boolean containsAll(Collection<?> arg0) { 
      boolean result = bolist.containsAll(arg0); 
      return result; 
     } 

     @Override 
     public boolean isEmpty() { 
      boolean result = bolist.isEmpty(); 
      return result; 
     } 

     @Override 
     public Iterator<BO_T> iterator() { 
      Iterator<BO_T> result = bolist.iterator(); 
      return result; 
     } 

     @Override 
     public boolean remove(Object arg0) { 
      boolean result = bolist.remove(arg0); 
      return result; 
     } 

     @Override 
     public boolean removeAll(Collection<?> arg0) { 
      boolean result = bolist.removeAll(arg0); 
      return result; 
     } 

     @Override 
     public boolean retainAll(Collection<?> arg0) { 
      boolean result = bolist.retainAll(arg0); 
      return result; 
     } 

     @Override 
     public int size() { 
      int result = bolist.size(); 
      return result; 
     } 

     @Override 
     public Object[] toArray() { 
      Object[] result = bolist.toArray(); 
      return result; 
     } 

     @Override 
     public <T> T[] toArray(T[] arg0) { 
      T[] result = bolist.toArray(arg0); 
      return result; 
     } 

    } 

    @XmlAccessorType(XmlAccessType.NONE) 
    @XmlTransient 
    public static abstract class MyMoxyManager<BO_T> extends 
      MoxyManagerImpl<BO_T> { 
     public abstract Class<? extends BO<?>> getEntityType(); 

    } 

    @XmlRootElement 
    public static class ItemManager extends MyMoxyManager<Item> implements 
      ItemManagerInterface { 
     public ItemManager() { 

     } 

     private List<Item> items = new ArrayList<Item>(); 

     @Override 
     @XmlElement 
     public void setItems(List<Item> pItems) { 
      items = pItems; 
     } 

     @Override 
     public List<Item> getItems() { 
      return items; 
     } 

     @SuppressWarnings("unchecked") 
     @Override 
     public Class<? extends BO<?>> getEntityType() { 
      return (Class<? extends BO<?>>) Item.class; 
     } 
    } 

    /** 
    * convert the target to XML Format 
    * 
    * @param target 
    * @return 
    * @throws Exception 
    */ 
    public String asXML(Object target) throws Exception { 
     JAXBContext jaxbContext = JAXBContext.newInstance(target.getClass()); 
     Marshaller jaxbMarshaller = jaxbContext.createMarshaller(); 
     // output pretty printed 
     jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); 
     StringWriter sw = new StringWriter(); 
     jaxbMarshaller.marshal(target, sw); 
     String result = sw.toString(); 
     return result; 
    } 

    @Test 
    public void testMarshall() throws Exception { 
     ItemManager im = new ItemManager(); 
     im.items.add(new Item(2)); 
     String xml = asXML(im); 
     System.out.println(xml); 
     assertNotEquals("xml should not be empty", "", xml); 
    } 

}

來源

2013-10-13 Wolfgang Fahl