Java 放在 getter 与 setter 与成员上的 JAXB 注释之间有什么区别？
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What's the difference between JAXB annotations put on getter versus setters versus members?
提问by stewenson
Title says it all.
标题说明了一切。
I would like to know what is the principial difference between putting JAXB annotation (like @XmlElement) on field / getter / setter. It seems to me that (in simple cases) it does not matter.
我想知道将 JAXB 注释（如@XmlElement）放在 field/getter/setter 上的主要区别是什么。在我看来（在简单的情况下）这无关紧要。
E.g. lets take this
例如让我们把这个
class A {
private String a;
public String getA() { return a; }
public void setA(String a) { this.a = a; }
}
now it seems to me that it does not matter if I put @XmlElementon member field or on getter / setter. It just marshalls ok. Are there any usecases when I need to make difference and when it does matter?
现在在我看来，我是放在@XmlElement成员字段上还是放在 getter/setter 上都没有关系。它只是编组确定。当我需要有所作为并且何时重要时，是否有任何用例？
When I go to unmarshall this (xml back to A) what JAXB does specifically?
当我去解组这个（xml回到A）JAXB具体做什么？
I am using JAXB MOXy implementation
我正在使用 JAXB MOXy 实现
Thanks
谢谢
采纳答案by bdoughan
By default JAXB impls will treat properties (get/set pairs), public fields (instance variables), and annotated non-public fields as mapped. If you just annotate a field you will get a duplicate mapped property exception.
默认情况下，JAXB 实现会将属性（获取/设置对）、公共字段（实例变量）和带注释的非公共字段视为映射。如果你只是注释一个字段，你会得到一个重复的映射属性异常。
If you want to annotate the field you should specify @XmlAccessorType(XmlAccessType.FIELD)on the class.
如果要注释该字段，则应@XmlAccessorType(XmlAccessType.FIELD)在类中指定。
For More Information
想要查询更多的信息
回答by Rahul Khimasia
I have found no differences in marking JAXB annotations on setter methods and getter methods. I tested both marshalling and unmarshalling, and they both worked fine. But you should only annotate one of them; either the getter method or the setter method; you cannot annotate both, else you will get a runtime exception like the following.
我发现在 setter 方法和 getter 方法上标记 JAXB 注释没有区别。我测试了编组和解组，它们都运行良好。但是你应该只注释其中一个；getter 方法或 setter 方法；您不能同时注释两者，否则您将收到如下所示的运行时异常。
com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:91)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:445)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:277)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:124)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1123)
at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:147)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
at javax.xml.bind.ContextFinder.find(ContextFinder.java:462)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
