问题

我有一个使用[Armeria][1]作为Web服务的Java应用程序。当我在主方法中创建Hibernate SessionFactory时，它运行正常。但是我试图在调用特定Http端点时创建SessionFactory。在处理程序方法中无法创建会话工厂。
`Exception in thread "Thread-1" org.hibernate.internal.util.config.ConfigurationException: 无法在资源hibernate.cfg.xml的行号0和列号0执行解组。消息：null`

由于: javax.xml.bind.JAXBException

• 附带链接的异常:
  [java.lang.ClassNotFoundException: com/sun/xml/bind/v2/ContextFactory]
  at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:226)
  at javax.xml.bind.ContextFinder.find(ContextFinder.java:441)
  at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
  at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
  at org.hibernate.boot.cfgxml.internal.JaxbCfgProcessor.unmarshal(JaxbCfgProcessor.java:122)
  ... 17 more
  由于: java.lang.ClassNotFoundException: com/sun/xml/bind/v2/ContextFactory
  at java.lang.Class.forName0(Native Method)
  at java.lang.Class.forName(Class.java:264)
  at javax.xml.bind.ContextFinder.safeLoadClass(ContextFinder.java:577)
  at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:224)
  ... 21 more

关于这个错误，我能找到的所有信息都是JaxB在Java 8之后不再提供，但我正在使用Java 8，如果我只是在应用程序启动时创建它，它就可以正常运行。

  [1]: https://github.com/line/armeria


<details>
<summary>英文:</summary>

I have a Java Application that uses [Armeria][1] for a Web Service. When I create my Hibernate SessionFactory in the main method it works fine. But I am trying to create the SessionFactory when a certain Http Endpoint is called. In the handler method the session factory can not be created
`Exception in thread &quot;Thread-1&quot; org.hibernate.internal.util.config.ConfigurationException: Unable to perform unmarshalling at line number 0 and column 0 in RESOURCE hibernate.cfg.xml. Message: null`

Caused by: javax.xml.bind.JAXBException

• with linked exception:
  [java.lang.ClassNotFoundException: com/sun/xml/bind/v2/ContextFactory]
  at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:226)
  at javax.xml.bind.ContextFinder.find(ContextFinder.java:441)
  at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
  at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
  at org.hibernate.boot.cfgxml.internal.JaxbCfgProcessor.unmarshal(JaxbCfgProcessor.java:122)
  ... 17 more
  Caused by: java.lang.ClassNotFoundException: com/sun/xml/bind/v2/ContextFactory
  at java.lang.Class.forName0(Native Method)
  at java.lang.Class.forName(Class.java:264)
  at javax.xml.bind.ContextFinder.safeLoadClass(ContextFinder.java:577)
  at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:224)
  ... 21 more

All I could find about this error is that JaxB is not provided for Java > 8 but i am using Java 8 and it works fine if I just create it at Application launch.

  [1]: https://github.com/line/armeria

</details>


# 答案1
**得分**: 3

我认为这是某种类路径冲突。在Java 8中，以下代码会因为`ClassNotFoundException: com/sun/xml/bind/v2/ContextFactory`而失败，正如问题中所报告的：

```lang-java
public class MyService {
    @Get("/start")
    public HttpResponse start() throws Exception {
        final StandardServiceRegistryBuilder registryBuilder =
            new StandardServiceRegistryBuilder().configure();
        ...
    }
}

然而，在升级到较新的Java版本（例如Java 11）后，问题就消失了。

幸运的是，可以通过显式地指定上下文类加载器来解决这个问题：

    @Get("/start")
    public HttpResponse start() throws Exception {
        Thread.currentThread().setContextClassLoader(MyService.class.getClassLoader());
        // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        final StandardServiceRegistryBuilder registryBuilder =
            new StandardServiceRegistryBuilder().configure();
        ...
    }

public class MyService {
    @Get("/start")
    public HttpResponse start() throws Exception {
        final StandardServiceRegistryBuilder registryBuilder =
            new StandardServiceRegistryBuilder().configure();
        ...
    }
}

    @Get("/start")
    public HttpResponse start() throws Exception {
        Thread.currentThread().setContextClassLoader(MyService.class.getClassLoader());
        // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        final StandardServiceRegistryBuilder registryBuilder =
            new StandardServiceRegistryBuilder().configure();
        ...
    }