在字段之前和在 getter 声明之前使用 @XmlElement 有什么区别? [英] What is the difference between using @XmlElement before field and before getter declaration?

问题描述

我可以通过两种方式声明 JAXB 元素:

I can declare JAXB element in two ways:

@XmlElement
public int x;

或

private int x;

@XmlElement
public int getX(){...}

第一个变体，AFAIK，创建 getter，映射到 XML，无论如何.这两种方式有什么区别?

The first variant, AFAIK, creates getter, mapped to XML, anyway. What is the difference between these two ways?

推荐答案

与@XmlAccessorType注解有关.

• XmlAccessType.PROPERTY :字段仅在被某些 JAXB 注释显式注释时才绑定到 XML.

• XmlAccessType.PROPERTY : Fields are bound to XML only when they are explicitly annotated by some of the JAXB annotations.

XmlAccessType.FIELD:只有在某些 JAXB 注释明确注释时，Getter/setter 对才绑定到 XML

XmlAccessType.FIELD: Getter/setter pairs are bound to XML only when they are explicitly annotated by some of the JAXB annotations

根据评论更新解释:

让我们考虑一个如下所示的简单 xml:

Let's consider a simple xml that looks like this:

<root>
    <value>someValue</value>
</root>

我们有一个类:

@XmlRootElement(name = "root")
//@XmlAccessorType(XmlAccessType.PROPERTY)
@XmlAccessorType(XmlAccessType.FIELD)
public class DemoRoot {

    @XmlElement
    private String value;

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

如果您尝试使用 XmlAccessType.FIELD 和字段上方的 @XmlElement 注释来解组，那么您将可以很好地解组.

If you try to unmarshal using XmlAccessType.FIELD and the @XmlElement annotation above the field, then you will unmarshal fine.

如果您使用 XmlAccessType.PROPERTY，您将收到以下错误:

If you use XmlAccessType.PROPERTY you will receive the following error:

IllegalAnnotationsException: 1 计数 IllegalAnnotationExceptions 类有两个同名的属性值"

IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions Class has two properties of the same name "value"

这是因为它考虑了显式注释的 @XmlElement 字段值"和 getter/setter.

This is because it takes into consideration both the explicitly annotated with @XmlElement field 'value' and the getters/setters.

如果您将 @XmlElement 注释移动到 getter/setter 上，反之亦然.

And vice versa if you move the @XmlElement annotation on the getter/setter.

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