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java - jaxb 按类型解组到对象

问题描述

我想根据 xml 解析出不同的类型，当 header=1 然后是 User，header=2 然后是 Order 等，例如：

<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>

如何实现这个功能？

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

标签： javajaxb

解决方案

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，只需先获取标题，然后获取实体。不是很好，但可以使用。

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