JAXB 需要公共无参数构造函数做什么? [英] What JAXB needs a public no-arg constructor for?

问题描述

在编组期间，JAXB 需要公共无参数构造函数做什么?

What does JAXB need a public no-arg constructor for, during marshalling?

 Marshaller msh = ctx.createMarshaller();
 msh.marshal(object, System.out);

我传递的是一个对象，而不是一个类.为什么 JAXB 需要构造函数?构建什么?

I'm passing an object, not a class. Why does JAXB need a constructor? To construct what?

推荐答案

在编组操作期间，JAXB 实现不应需要无参数构造函数.JAXB 确实需要一个用于解组.通常，在创建 JAXBContext 时，缺少无参数构造函数会导致错误.您正在使用的 JAXB 实现可能会延迟初始化，直到执行实际操作.

A JAXB implementation should not need a no-arg constructor during a marshal operation. JAXB does require one for unmarshalling. Normally the absence of a no-arg constructor causes an error when the JAXBContext is created. The JAXB implementation you are using may be delaying initialization until an actual operation is performed.

总的来说，我们应该在 JAXB 的未来版本中考虑对多参数构造函数的支持.在 JAXB (MOXy) 的 EclipseLink 实现中，我们为此功能打开了一个增强请求(随意添加相关的详情):

In general support for multi-arg constructors is something we should consider in a future version of JAXB. In the EclipseLink implementation of JAXB (MOXy) we have an enhancement request open for this functionality (feel free to add relevant details):

• https://bugs.eclipse.org/328951.

在当前版本的 JAXB 中，您可以使用 XmlAdapter 来支持此用例:

In the current version of JAXB you could use an XmlAdapter to support this use case:

• http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html

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