jaxb按类型解组到对象

编程问答 2022-07-26

问题描述

我想基于xml解析不同的类型，例如，当header = 1然后是User，header = 2然后是Order等。

<entity>
  <header>1</header>
  <body>
    <userId>1</userId>
    <userName>jonh</userName>
    ...
  <body>
</entity>

<entity>
  <header>2</header>
  <body>
    <orderId>1</orderId>
    <orderNo>20200101</orderNo>
    ...
  <body>
</entity>

如何实现此功能？

Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
Object object = unmarshaller.unmarshal(xml);

解决方法

我会尝试：在解组时提供类型。因此，也许可以执行以下操作：创建一个临时外观对象：

public class XmlEntityFacade {

   private int header;
   private Object body;

   //getters and setters...

}

然后在解组时强制转换此类型：

...
XmlEntityFacade facade = (XmlEntityFacade) unmarshaller.unmarshal(xml);

然后，您可以通过调用.getHeader（）和带有.getBody（）的正文（您已提供XmlEntityFacade类的getter）来访问的值。然后根据值将所需的类型强制转换为对象。

, 
public class TwiceUnmarshalTest {

    @Data
    @ToString
    public static abstract class HeaderResponse {
        private String header;
    }

    @XmlRootElement(name = "entity")
    @XmlAccessorType(XmlAccessType.FIELD)
    public static class XmlHeaderResponse extends HeaderResponse {
    }

    private final String xml = "<entity>" +
            "  <header>2</header>" +
            "  <body>" +
            "    <orderId>1</orderId>" +
            "    <orderNo>2020</orderNo>" +
            "  </body>" +
            "</entity>";

    @SuppressWarnings("unchecked")
    public static <T> T unmarshal(Reader reader,Class<T> typeClass) throws Exception {
        JAXBContext jaxbContext = JAXBContext.newInstance(typeClass);
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        return (T) unmarshaller.unmarshal(reader);
    }

    @Test
    public void headerResponse() throws Exception {
        HeaderResponse response = unmarshal(new StringReader(xml),XmlHeaderResponse.class);
        System.out.println(response);
    }

    @ToString(callSuper = true)
    public static abstract class Response<T> extends HeaderResponse {
        @XmlAnyElement(lax = true)
        public T body;
    }

    @Data
    @XmlRootElement(name = "body")
    public static class Order {
        private String orderId;
        private String orderNo;

    }

    @XmlRootElement(name = "entity")
    @XmlSeeAlso({Order.class})
    public static class OrderResponse extends Response<Order> {
    }

    @Test
    public void response() throws Exception {
        XmlHeaderResponse response = unmarshal(new StringReader(xml),XmlHeaderResponse.class);
        System.out.println(response);
        //TwiceUnmarshalTest.HeaderResponse(header=2)
        if (response.getHeader().equals("2")) {
            OrderResponse orderResponse = unmarshal(new StringReader(xml),OrderResponse.class);
            System.out.println(orderResponse);
  //TwiceUnmarshalTest.Response(super=TwiceUnmarshalTest.HeaderResponse(header=2),body=TwiceUnmarshalTest.Order(orderId=1,orderNo=2020))
        }
    }
}

解组两次，只需先获取标头，然后获取实体。不太好，但是可以使用。