JAXB编组和泛型 [英] JAXB Marshalling and Generics

问题描述

我试图使用JAXB的自省对marshall进行反编译并取消对JAXB注释标记的某些现有域对象的解除。大多数事情都按预期工作，但是我得到一个相当简单的类来序列化时遇到了一些麻烦。这个类在许多bean上用作@XmlElement，看起来像这样：

  public class Range< E extends Comparable< E  - 代替;>实现Serializable {
 protected boolean startInclusive，endInclusive; 
保护E开始，结束; 
 
 public Range（）{
 startInclusive = endInclusive = true; 
 
 $ b $ public boolean contains（E value）{...} 
 
 public E getEnd（）{
 return end; 
} 
 
 public void setEnd（E end）{
 this.end = end; 
} 
 
 public boolean isEndInclusive（）{
 return endInclusive; 
} 
 
 public void setEndInclusive（boolean endInclusive）{
 this.endInclusive = endInclusive; 
} 
 
 public E getStart（）{
 return start; 
} 
 
 public void setStart（E start）{
 this.start = start; 
} 
 
 public boolean isStartInclusive（）{
 return startInclusive; 
} 
 
 public void setStartInclusive（boolean startInclusive）{
 this.startInclusive = startInclusive; 
} 
} 
  

我试图做到以下几点，但没有成功，JAXB仍然对Comparable接口感到愤怒。

  public class DoubleRange extends Range< Double> {} 
  

使用Range和DoubleRange作为bean getter的返回类型会产生如下异常： p>

 
 java.lang.Comparable是一个接口，JAXB无法处理接口。 
此问题与以下位置有关：
在java.lang.Comparable $ b $ protected at protected java.lang.Comparable com.controlpath.util.Range.start 
 at example。 util.Range 
 at example.util.DoubleRange 
 at public example.util.DoubleRange example.domain.SomeBean.getRange（）
 at example.domain.SomeBean 
 

我知道在大多数情况下，List< T>和Map< T，U>因为JAXB规范在遇到bean时对这些类型有特殊的规定，但是有什么方法可以传达我想要的JAXB自省引擎，而不必使用非泛型字段来实现范围？

解决方案

通过执行以下操作， p> 1）声明一个接受各种元素并拥有JAXB注释
的类并按照你的意愿处理它们（在我的例子中，我将所有东西都转换为字符串）

  @YourJAXBAnnotationsGoHere 
 public class MyAdapter {
 
 @XmlElement //或@XmlAttribute如果您希望
私有字符串内容; 
 $ b $ public MyAdapter（Object input）{
 if（input instanceof String）{
 content =（String）input; 
} else if（输入instanceof YourFavoriteClass）{
 content =（（YourFavoriteClass）input）.convertSomehowToString（）; 
} else if（input instanceof .....）{
 content =（（.....）input）.convertSomehowToString（）; 
 //等等
} else {
 content = input.toString（）; 
} 
} 
} 
 
 //我建议使用Map< Class<>，IMyObjToStringConverter> ... 
 //避免讨厌的if-else-instanceof事物
  

<2>使用这个类而不是E在你要编组的类中

NOTES

• 当然，这对于复杂的（嵌套的）数据结构是 not 。


• 你必须考虑如何解组，可能会更棘手。如果
  太棘手，请等待比我更好的提案;）
  
  

  I am trying to use JAXB's introspection to marshall and unmashall some existing domain objects marked up with JAXB annotations. Most things work as expected, but I am having quite a bit of trouble getting a fairly simple class to serialize. This class is used as an @XmlElement on a number of beans and looks something like:

  public class Range<E extends Comparable<E>> implements Serializable {
      protected boolean startInclusive, endInclusive;
      protected E       start, end;
  
      public Range(){
              startInclusive = endInclusive = true;
      }
  
      public boolean contains(E value){...}
  
      public E getEnd() {
              return end;
      }
  
      public void setEnd(E end) {
              this.end = end;
      }
  
      public boolean isEndInclusive() {
              return endInclusive;
      }
  
      public void setEndInclusive(boolean endInclusive) {
              this.endInclusive = endInclusive;
      }
  
      public E getStart() {
              return start;
      }
  
      public void setStart(E start) {
              this.start = start;
      }
  
      public boolean isStartInclusive() {
              return startInclusive;
      }
  
      public void setStartInclusive(boolean startInclusive) {
              this.startInclusive = startInclusive;
      }
  }
  

  I have tried to do the following, with no success, JAXB is still angry with the interface Comparable.

  public class DoubleRange extends Range<Double> {}
  

  Using both Range and DoubleRange as return types for the bean getter's yields an exception like:

  java.lang.Comparable is an interface, and JAXB can't handle interfaces.
      this problem is related to the following location:
          at java.lang.Comparable
          at protected java.lang.Comparable com.controlpath.util.Range.start
          at example.util.Range
          at example.util.DoubleRange
          at public example.util.DoubleRange example.domain.SomeBean.getRange()
          at example.domain.SomeBean
  

  I realize that in most cases List<T> and Map<T, U> only work because the JAXB specification has special provisions for those types when they are encountered on beans, but is there any way to convey what I want to the JAXB introspection engine without having to reimplement range with non-generic fields?

  解决方案

  You could write a custom adapter (not using JAXB's XmlAdapter) by doing the following:

  1) declare a class which accepts all kinds of elements and has JAXB annotations and handles them as you wish (in my example I convert everything to String)

  @YourJAXBAnnotationsGoHere
  public class MyAdapter{
  
    @XmlElement // or @XmlAttribute if you wish
    private String content;
  
    public MyAdapter(Object input){
      if(input instanceof String){
        content = (String)input;
      }else if(input instanceof YourFavoriteClass){
        content = ((YourFavoriteClass)input).convertSomehowToString();
      }else if(input instanceof .....){
        content = ((.....)input).convertSomehowToString();
      // and so on
      }else{
        content = input.toString();
      }
    }
  }
  
  // I would suggest to use a Map<Class<?>,IMyObjToStringConverter> ...
  // to avoid nasty if-else-instanceof things
  

  2) use this class instead of E in your to-be-marshalled class

  NOTES

  • Of course this would not work for complex (nested) data structures.
  • You have to think how to unmarshall this back again, could be more tricky. If it's too tricky, wait for a better proposal than mine ;)

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