JAXB和复合模式

问题描述

我现在正在使用JAXB，我正在努力注释我的复合前提条件查询概念，以便JAXB会很高兴。

I'm working with JAXB right now and I'm struggling to annotate my composite notion of precondition query so that JAXB would be happy.

前置条件查询可以be：

A precondition query can be:

• simple：只包含查询的文本节点


• 复合
  
  
  
  • OR：1前置条件查询或其他匹配的前提条件
  
  
  • AND：1前置条件查询和其他匹配的前提条件
  
  

  当然，复合查询可以由复合查询组成，就像下面的例子一样：

  Of course, compound queries can be made of compound queries, just like in the following example:

      <precondition>
          <or>
              <and>
                  <query>foo</query>
                  <query>bar</query>
              </and>
              <query>baz</query>
          </or>
      </precondition>
  

  在我的Java模型中，我有一个带注释的单一接口PreconditionQuery（实际上是一个自JAXB以来的抽象类）似乎不满意接口）有3个实现SimplePreconditionQuery，CompoundOrPreconditionQuery和CompoundAndPreconditionQuery。

  In my Java model, I've got a single interface annotated PreconditionQuery (actually an abstract class since JAXB seems unhappy with interfaces) with 3 implementations SimplePreconditionQuery, CompoundOrPreconditionQuery and CompoundAndPreconditionQuery.

  @XmlSeeAlso(PreconditionQuery.class)
  @XmlRootElement(name = "query")
  public class SimplePreconditionQuery extends PreconditionQuery {
  
      private String query;
  
      @XmlValue
      public String getQuery() {
          return query;
      }
  
      public void setQuery(String query) {
          this.query = query;
      }
  }
  

  对于复合的（CompoundOrPreconditionQuery基本相同） ：

  For the compound ones (CompoundOrPreconditionQuery is basically the same):

  @XmlSeeAlso(PreconditionQuery.class)
  @XmlRootElement(name = "and")
  public class CompoundAndPreconditionQuery extends PreconditionQuery {
  
      private Collection<PreconditionQuery> preconditionQueries = newArrayList();
  
      @XmlElementRef(name = "query")
      public Collection<PreconditionQuery> getPreconditionQueries() {
          return preconditionQueries;
      }
  
      public void setPreconditionQueries(Collection<PreconditionQuery> preconditionQueries) {
          this.preconditionQueries = preconditionQueries;
      }
  }
  

  最后，在封闭的bean级别，我映射为这个：

  Finally, at the enclosing bean level, I mapped like this:

  public class Precondition {
  
      private PreconditionQuery query;
  
      @XmlElementRef(required = true)
      public PreconditionQuery getQuery() {
          return query;
      }
  
      public void setQuery(PreconditionQuery query) {
          this.query = query;
      }
  }
  

  最后，JAXB抱怨无法解决这个问题：

  In the end, JAXB complains about not being able to resolve this:

  Caused by: com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
  Invalid @XmlElementRef : Type "class xxx.PreconditionQuery" or any of its subclasses are not known to this context.
      this problem is related to the following location:
          at public xxx.PreconditionQuery xxx.Precondition.getQuery()
          at xxx.Precondition
  

  如果 @XmlElementRef 不能完成这项工作，那会是什么？

  If @XmlElementRef doesn't do the job, what will?

  推荐答案

  请尝试添加

  @XmlSeeAlso({PreconditionQuery.class})
  

  到 CompoundAndPreconditionQuery 类。

  然后，尝试使用 @XmlRootElement注释所有 PreconditionQuery 类/子类。

  Then, try annotating ALL of your PreconditionQuery classes/subclasses with @XmlRootElement.

  另外，对于 @XmlAccessorType 要小心一点 - 有时候你有，有时不。用它来更好地注释包。

  Also, be a bit more careful with @XmlAccessorType - sometimes you have it, sometimes not. Better annotate the package with it.

  最后，你可能需要 ObjectFactory 和 @ XmlRegistry 和 @XmlElementDecl ，但我认为这绝对不是必需的。

  Finally, you may need an ObjectFactory with @XmlRegistry and @XmlElementDecl, but I do not think it is absolutely required.

  我认为问题是缺少 @XmlRootElement / @XmlSeeAlso 注释。

  I think the problem is the missing @XmlRootElement/@XmlSeeAlso annotations.

  @XmlElementRef 已知很棘手，但确实有效。 ：）

  @XmlElementRef is known to be tricky, but it does work for sure. :)

  祝你好运和祝福。

  这篇关于JAXB和复合模式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！