如何使用 JAXB2 将 XML 与动态元素编组

Question

我正在开发一个 SOAP 客户端，我正在寻找更复杂的解决方案来使用 Jaxb2 库将对象编组为 XML-string。

目标是整理一个对象，该对象充当任何类型元素的包装器。示例：

<Action id="5">
   <Employee id="10">
      <Name>John</Name>
   </Employee>
</Action>

或.

 <Action id="5">
    <Department id="ABC">
       <Name>Economy Department</Name>
       <ParentId>CDE</ParentId>
    </Department>
 </Action>

注意：xml 根（操作）包含“员工”或“部门”或其他任何内容。

我目前的工作方案如下：

@XmlRootElement(name = "Action")
abstract class Action {

   @XmlAttribute(name = "id")
   protected String id;

}

class EmployeeAction extends Action {
    
   @XmlElement(name = "Employee")
   protected Employee employee;

}

class DepartmentAction extends Action {
    
   @XmlElement(name = "Department")
   protected Department department;

}

这很好用，但我正在寻找更通用的解决方案，而不需要为每种类型创建 class（*Action extends Action）。元素的名称必须始终与（动态）类型的 class 名称相同。我的想法是这样的：

public class Action<T> {

   @XmlAttribute(name = "id")
   protected String id;

   @XmlElement(name = "getClass().getSimpleName()") //???
   protected T element;

}

... 并编组如下内容：

Action<?> action = ...;

JAXBContext context = JAXBContext.newInstance(Action.class, action.getElement().getClass());
Marshaller marshaller = context.createMarshaller();

try(ByteArrayOutputStream outStream = new ByteArrayOutputStream()) {
   marshaller.marshal(action, outStream);
   return outStream.toString();
}

这样的事情可能吗？

提前致谢。

Answer 1

对于上面提供的XML:

你可以这样做

方法一

Action.class;

@XmlRootElement(name = "Action")
@Data
@XmlAccessorType(XmlAccessType.FIELD)
public class Action {
    @XmlAttribute(name = "id")
    protected String id;

    @XmlElements({
            @XmlElement(name = "Employee", type = Employee.class),
            @XmlElement(name = "Department", type = Department .class),
    })
    private ActionItem type;
}

ActionItem.class;

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class ActionItem {
    @XmlElement(name = "Name")
    protected String name;
}

Employee.class;

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Employee extends ActionItem {

    @XmlAttribute(name = "id")
    private String id;
}

Department.class;

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Department extends ActionItem {
    @XmlAttribute
    private String id;

    @XmlElement(name = "ParentId")
    private String parentID;
}

Main.class:


public class Main {
    public static void main(String[] args) throws JAXBException, XMLStreamException {
        final InputStream inputStream = Unmarshalling.class.getClassLoader().getResourceAsStream("action.xml");
        final XMLStreamReader xmlStreamReader = XMLInputFactory.newInstance().createXMLStreamReader(inputStream);
        final Unmarshaller unmarshaller = JAXBContext.newInstance(Action.class).createUnmarshaller();
        final Action action = unmarshaller.unmarshal(xmlStreamReader, Action.class).getValue();
        System.out.println(action.toString());

        Marshaller marshaller = JAXBContext.newInstance(Action.class).createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
        marshaller.marshal(action, System.out);
    }
}

如果您提供 Employee XML 那么它会产生以下结果：

Action(id=5, type=Employee(id=10))
<Action id="5">
   <Employee id="10">
      <Name>John</Name>
   </Employee>
</Action>

如果您提供 Department XML 那么它会产生以下结果：

Action(id=5, type=Department(parentID=CDE))
<Action id="5">
   <Department>
      <Name>Economy Department</Name>
      <ParentId>CDE</ParentId>
   </Department>
</Action>

方法二

创建界面并使用它：

public interface ActionItem2 {
}

Action.class 使用创建的界面。

@XmlRootElement(name = "Action")
@Data
@XmlAccessorType(XmlAccessType.FIELD)
public class Action {
    @XmlAttribute(name = "id")
    protected String id;

    @XmlElements({
            @XmlElement(name = "Employee", type = Employee.class),
            @XmlElement(name = "Department", type = Department .class),
    })
    private ActionItem2 type;
}

Employee.class实现创建的接口

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Employee implements ActionItem2 {

    @XmlAttribute(name = "id")
    private String id;

    @XmlElement(name = "Name")
    protected String name;
}

Department.class实现创建的接口

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Department implements ActionItem2 {
    @XmlAttribute
    private String id;

    @XmlElement(name = "ParentId")
    private String parentID;

    @XmlElement(name = "Name")
    protected String name;
}

Main.class（无变化）

public class Main {
    public static void main(String[] args) throws JAXBException, XMLStreamException {
        final InputStream inputStream = Unmarshalling.class.getClassLoader().getResourceAsStream("action.xml");
        final XMLStreamReader xmlStreamReader = XMLInputFactory.newInstance().createXMLStreamReader(inputStream);
        final Unmarshaller unmarshaller = JAXBContext.newInstance(Action.class).createUnmarshaller();
        final Action action = unmarshaller.unmarshal(xmlStreamReader, Action.class).getValue();
        System.out.println(action.toString());

        Marshaller marshaller = JAXBContext.newInstance(Action.class).createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
        marshaller.marshal(action, System.out);
    }
}

结果是一样的。

方法 - 3

如果你不想修改你的 POJO，那么你可以这样做：

@XmlRootElement(name = "Action")
@Data
@XmlAccessorType(XmlAccessType.FIELD)
public class Action {
    @XmlAttribute(name = "id")
    protected String id;

    @XmlElements({
            @XmlElement(name = "Employee", type = Employee.class),
            @XmlElement(name = "Department", type = Department .class),
    })
    private Object type;
}

Employee.class:

@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Employee {

    @XmlAttribute(name = "id")
    private String id;

    @XmlElement(name = "Name")
    protected String name;
}

Department.class:


@Data
@XmlAccessorType(XmlAccessType.NONE)
public class Department {

    @XmlAttribute
    private String id;

    @XmlElement(name = "ParentId")
    private String parentID;

    @XmlElement(name = "Name")
    protected String name;
}

这将提供相同的输出。

如何使用 JAXB2 将 XML 与动态元素编组

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