JAXB将Xml和实体类相互转化的笔记

2021-11-29 约 1075 字预计阅读 3 分钟次阅读

JAXB是什么？

JAXB（即Java Architecturefor XML Binding）是一个业界的标准，即是一项可以根据XML Schema产生Java类的技术。该过程中，JAXB也提供了将XML实例文档反向生成Java对象树的方法，并能将Java对象树的内容重新写到XML实例文档。

使用举例

实体类

父节点

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@Data
@AllArgsConstructor
@NoArgsConstructor
@Component
@XmlRootElement(name = "Xml")
@ApiModel("XML对象")
public class XMLEty {

    @XmlElement(name = "Header")
    private Header header;
    @XmlElement(name = "Body")
    private Body body;

    @XmlTransient
    public Header getHeader() {
        return header;
    }

    @XmlTransient
    public Body getBody() {
        return body;
    }
}

头节点

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@Data
@AllArgsConstructor
@NoArgsConstructor
public class Header {
    @XmlElement(name = "b")
    String b;

    @XmlTransient
    public String getB() {
        return b;
    }
}

身体节点

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@Data
@AllArgsConstructor
@NoArgsConstructor
public class Body {
    @XmlElement(name = "a")
    String a;

    @XmlTransient
    public String getA() {
        return a;
    }
}

业务逻辑（Controller）

实体类到XML

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@PostMapping("/re")
public String reIndex() {
    String result = "null";
    StringWriter writer = new StringWriter();
    Header header = new Header("B-Header");
    Body body = new Body("A-Body");
    XMLEtyReq xml = new XMLEtyReq(header,body);
    Marshaller m = null;
    try {
        JAXBContext context = JAXBContext.newInstance(XMLEtyReq.class);
        m = context.createMarshaller();
        m.marshal(xml, writer);
        result = writer.toString();
    } catch (JAXBException ex) {
        ex.printStackTrace();
    }
    return result;
}

XML到实体类

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@PostMapping("/")
public String index(@RequestBody JSONObject jsonObj) {
    Unmarshaller uma = null;
    Object obj = null;
    try {
        JAXBContext jc = JAXBContext.newInstance(XMLEty.class);
        uma = jc.createUnmarshaller();
        String param = jsonObj.getString("param");
        obj = uma.unmarshal(new StringReader(param));
    } catch (JAXBException e) {
        e.printStackTrace();
    }
    return ((XMLEty) obj).toString();
}

注：

多层通过类的嵌套实现

内部类需要定义为static

使用@XmlTransient注解它会为它的target阻止绑定操作，这个target可以是一个class或者一个field或者一个method。否则会报错：JAXB 有两个名为XX的属性，类的两个属性具有相同名称XX详情点我

其他注解

XmlTransient

设置getter/setter不和xml绑定，类似ORM框架中Transient注解，

XmlAccessorType

Controls whether fields or Javabean properties are serialized by default.

控制是否默认序列化字段或者Javabean 的属性（四种情况如下）

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    /**
     * Every getter/setter pair in a JAXB-bound class will be automatically
     * bound to XML, unless annotated by {@link XmlTransient}.
     *
     * Fields are bound to XML only when they are explicitly annotated
     * by some of the JAXB annotations.
     */
    PROPERTY,
    /**
     * Every non static, non transient field in a JAXB-bound class will be automatically
     * bound to XML, unless annotated by {@link XmlTransient}.
     *
     * Getter/setter pairs are bound to XML only when they are explicitly annotated
     * by some of the JAXB annotations.
     */
    FIELD,
    /**
     * Every public getter/setter pair and every public field will be
     * automatically bound to XML, unless annotated by {@link XmlTransient}.
     *
     * Fields or getter/setter pairs that are private, protected, or
     * defaulted to package-only access are bound to XML only when they are
     * explicitly annotated by the appropriate JAXB annotations.
     */
    PUBLIC_MEMBER,
    /**
     * None of the fields or properties is bound to XML unless they
     * are specifically  annotated with some of the JAXB annotations.
     */
    NONE

XmlAttribute

可以绑定属性到对应的标签

Java代码

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@XmlRootElement
@SuppressWarnings("serial")
public class TVenueEntity implements java.io.Serializable {
	private long venueId;
	@XmlAttribute(name = "venueId")
	public long getVenueId() {
		return venueId;
	}
}

生成的xml

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<tVenueEntity venueId="1132">
</tVenueEntity>

XmlElementWrpper

当属性是集合时如List、Set、Map等，需要在外层对多个内部对象进行包装，否则序列化报错

报错

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[javax.xml.bind.JAXBException: class java.util.HashSet nor any of its super class is known to this context.]