younker

笔者做好了一个Java Application的JAXB Project之后，想把它应用到Web Project中，用于实现我们实验室的构建库项目中的REST服务。本来以为三两下就可以搞定，没想到碰到一个怪异的异常，结果搞了整整一天才弄出来。故把它贴出来，希望对同样遇到这样问题的人有所帮助。

异常如下：

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception

root cause

java.lang.NoClassDefFoundError: javax/activation/DataSource

        com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl.<clinit>(RuntimeBuiltinLeafInfoImpl.java:172)

        com.sun.xml.bind.v2.model.impl.RuntimeTypeInfoSetImpl.<init>(RuntimeTypeInfoSetImpl.java:25)

        com.sun.xml.bind.v2.model.impl.RuntimeModelBuilder.createTypeInfoSet(RuntimeModelBuilder.java:78)

        com.sun.xml.bind.v2.model.impl.RuntimeModelBuilder.createTypeInfoSet(RuntimeModelBuilder.java:41)

        com.sun.xml.bind.v2.model.impl.ModelBuilder.<init>(ModelBuilder.java:97)

        com.sun.xml.bind.v2.model.impl.RuntimeModelBuilder.<init>(RuntimeModelBuilder.java:44)

        com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:320)

        com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:198)

        com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:76)

        com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:55)

        com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:124)

        sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

        sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

        sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

        java.lang.reflect.Method.invoke(Method.java:585)

        javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:132)

        javax.xml.bind.ContextFinder.find(ContextFinder.java:286)

        javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:358)

        javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:323)

        javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:244)

        RestServlet.doGet(RestServlet.java:78)

        javax.servlet.http.HttpServlet.service(HttpServlet.java:689)

        javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

note The full stack trace of the root cause is available in the Apache Tomcat/5.5.20 logs.

解决办法：将\jwsdp-2.0\jwsdp-shared\lib目录下的activation.jar拷贝到Tomcat 5.5\common\lib。
笔者征询了一些，觉得这个在application中可以运行，但是在web project却抛出异常的原因可能是：application加载xmlObj.component的时候用的是System的类加载器，web中用的是加载你这段程序的类加载器，两者类路径不同，造成这个错误