【发布时间】：2013-04-20 14:23:53
【问题描述】：
我正在开发一个非常简单的 Eclipse 插件，它使用 EclipseLink 的 MOXy 进行 XML 绑定（编组/解组）。当我在插件（Activator.java）的启动过程中尝试编组一个简单的类（Person.java）时，我遇到了几个错误。代码如下：
代码：
Person.java
package test_rcp;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class Person {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
Activator.java
package test_rcp;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import org.eclipse.ui.plugin.AbstractUIPlugin;
import org.osgi.framework.BundleContext;
public class Activator extends AbstractUIPlugin {
public void start(BundleContext context) throws Exception {
super.start(context);
plugin = this;
// Just to make sure EclipseLink is already loaded
System.out.println(org.eclipse.persistence.Version.getVersion());
Person p1 = new Person();
p1.setName("John Dewey");
p1.setAge(54);
JAXBContext jc = JAXBContext.newInstance("test_rcp",Person.class.getClassLoader());
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(p1, System.out);
}
}
MANIFEST.MF
Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Test-RCP
Bundle-SymbolicName: Test-RCP; singleton:=true
Bundle-Version: 1.0.0.qualifier
Bundle-Activator: test_rcp.Activator
Require-Bundle: org.eclipse.ui,
org.eclipse.core.runtime,
org.eclipse.persistence.core,
org.eclipse.persistence.moxy;bundle-version="2.4.1"
Bundle-ActivationPolicy: lazy
Bundle-RequiredExecutionEnvironment: JavaSE-1.7
包test_rcp还包含jaxb.index和jaxb.properties：
jaxb.index
Person
jaxb.properties
javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
问题：
但运行插件会引发以下异常：
javax.xml.bind.JAXBException: Provider org.eclipse.persistence.jaxb.JAXBContextFactory could not be instantiated:
javax.xml.bind.JAXBException: Provider class org.eclipse.persistence.jaxb.JAXBContextFactory could not be instantiated:
javax.xml.bind.JAXBException:
ClassCastException: attempting to cast bundleresource://43.fwk583158213/javax/xml/bind/JAXBContext.class to jar:file:/usr/lib/jvm/java-7-oracle/jre/lib/rt.jar!/javax/xml/bind/JAXBContext.class. Please make sure that you are specifying the proper ClassLoader.
我知道问题是由于两个类加载器已经加载了javax.xml.bind 包，但我不知道为什么以及如何避免这种情况。
Morover，通过使用JAXBContextFactory 而不是JAXBContext.newInstance（建议here），即：
JAXBContext jc = org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(new Class[] {Person.class}, null);
我会得到以下异常：
java.lang.LinkageError: loader constraint violation:
loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) previously
initiated loading for a different type with name "javax/xml/bind/JAXBContext"
我已经尝试了以下解决方案，但没有成功：
https://stackoverflow.com/a/12943115/2295964
https://stackoverflow.com/a/11797373/2295964
如果有人能帮助我摆脱这种痛苦，我将不胜感激！
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