简而言之：有没有办法告诉 WebSphere 使用来自应用程序自己的 el-api.jar 的类，而不是来自（内置）javax.j2ee.el.jar 的类？
故事：我知道在将应用程序从 WAS 6.1 迁移到 WAS 8 期间，互联网上有关于此问题的讨论，但他们都没有明确提及这一点：
当 WAS 8 尝试从 el-api.jar（包含在 EAR 中）加载 javax.el.ExpressionFactory 时，整个事情就卡住了。但是，此时它已经从 javax.j2ee.el.jar 加载了它。（这在 WAS 6.1 中不存在。）如果您打开详细类加载：
类加载：javax.el.ExpressionFactory 来自：file:/C:/Program Files/IBM/WebSphere/AppServer/plugins/javax.j2ee.el.jar（在您安装应用程序之前！）
看来，由于在安装包含 el-api.jar 的应用程序的 EAR 之前已经加载了后一个 jar，因此 WAS 8 偶然发现了类加载冲突，无论您是否指定它使用 PARENT_LAST 类加载策略与否。
我可以在其中使用 javax.j2ee.el.jar 而不是 el-api.jar 来编译和安装应用程序，但一方面我不知道这可能会产生什么长期后果（我没有能够让它以任何一种方式运行），另一方面，最终目标是能够在 WAS 8 服务器上安装原始 EAR（包含其自己的 JSF 库等），并且尽可能少地进行修改。
有没有办法告诉 WAS 8 服务器从 el-api.jar 重新加载应用程序中可能存在冲突的类，或者甚至不首先加载 javax.j2ee.el.jar？（就像我提到的，指定 PARENT_CLASS 对此没有任何影响。）
谢谢。
当 WAS 8 尝试从 el-api.jar 加载 javax.el.ExpressionFactory 时抛出的异常（启动已安装的应用程序时）：
（对不起，它是德语，一些谷歌搜索将此错误消息的英语版本标识为：
'java.lang.LinkageError: loading constraint violation: loader "com/ibm/ws/classloader/CompoundClassLoader@1ef123a" previously initiated loading for a different type with name "javax/el/ExpressionFactory" defined by loader org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader@1f75d64"')
java.lang.LinkageError: Übertretung der Ladeeinschränkung: Ladeprogramm "com/ibm/ws/classloader/CompoundClassLoader@1ef123a" hat zuvor das Laden für einen anderen Typ mit dem Namen "javax/el/ExpressionFactory", der durch Ladeprogramm "org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader@1f75d64" definiert ist, eingeleitet.
at java.lang.ClassLoader.defineClassImpl(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:262)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:69)
at com.ibm.ws.classloader.CompoundClassLoader._defineClass(CompoundClassLoader.java:829)
at com.ibm.ws.classloader.CompoundClassLoader.localFindClass(CompoundClassLoader.java:744)
at com.ibm.ws.classloader.CompoundClassLoader.loadClass(CompoundClassLoader.java:585)
at java.lang.ClassLoader.loadClass(ClassLoader.java:627)
at java.lang.Class.getDeclaredFieldsImpl(Native Method)
at java.lang.Class.getDeclaredFields(Class.java:546)
at com.ibm.ffdc.util.formatting.Introspector$1.run(Introspector.java:138)
at com.ibm.ffdc.util.formatting.Introspector$1.run(Introspector.java:136)
at java.security.AccessController.doPrivileged(AccessController.java:254)
at com.ibm.ffdc.util.formatting.Introspector.getDeclaredFields(Introspector.java:135)
at com.ibm.ffdc.util.formatting.Introspector.formatTo(Introspector.java:94)
at com.ibm.ffdc.util.provider.IncidentStream$2.writeTo(IncidentStream.java:194)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:198)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:129)
at com.ibm.ffdc.util.formatting.JavaUtilFormatter.formatTo(JavaUtilFormatter.java:56)
at com.ibm.ffdc.util.formatting.JavaUtilFormatter.formatTo(JavaUtilFormatter.java:42)
at com.ibm.ffdc.util.provider.IncidentStream$2.writeTo(IncidentStream.java:194)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:198)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:129)
at com.ibm.ffdc.util.formatting.Introspector.formatTo(Introspector.java:109)
at com.ibm.ffdc.util.provider.IncidentStream$2.writeTo(IncidentStream.java:194)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:198)
at com.ibm.ffdc.util.provider.IncidentStream.write(IncidentStream.java:129)
at com.ibm.ws.ffdc.impl.DMAdapter.formatTo(DMAdapter.java:88)
at com.ibm.ffdc.util.provider.IncidentLogger.writeIncidentTo(IncidentLogger.java:63)
at com.ibm.ws.ffdc.impl.FfdcProvider.logIncident(FfdcProvider.java:205)
at com.ibm.ws.ffdc.impl.FfdcProvider.logIncident(FfdcProvider.java:136)
at com.ibm.ffdc.util.provider.FfdcProvider.log(FfdcProvider.java:251)
at com.ibm.ws.ffdc.impl.FfdcProvider.log(FfdcProvider.java:149)
at com.ibm.ffdc.util.provider.IncidentEntry.log(IncidentEntry.java:105)
at com.ibm.ffdc.util.provider.Ffdc.log(Ffdc.java:94)
at com.ibm.ws.ffdc.FFDCFilter.processException(FFDCFilter.java:114)
at com.ibm.wsspi.webcontainer.util.FFDCWrapper.processException(FFDCWrapper.java:6)
at com.ibm.ws.webcontainer.webapp.WebApp.notifyServletContextCreated(WebApp.java:1653)
at com.ibm.ws.webcontainer.webapp.WebAppImpl.initialize(WebAppImpl.java:410)
at com.ibm.ws.webcontainer.webapp.WebGroupImpl.addWebApplication(WebGroupImpl.java:88)
at com.ibm.ws.webcontainer.VirtualHostImpl.addWebApplication(VirtualHostImpl.java:169)
at com.ibm.ws.webcontainer.WSWebContainer.addWebApp(WSWebContainer.java:746)
at com.ibm.ws.webcontainer.WSWebContainer.addWebApplication(WSWebContainer.java:634)
at com.ibm.ws.webcontainer.component.WebContainerImpl.install(WebContainerImpl.java:422)
at com.ibm.ws.webcontainer.component.WebContainerImpl.start(WebContainerImpl.java:714)
at com.ibm.ws.runtime.component.ApplicationMgrImpl.start(ApplicationMgrImpl.java:1160)
at com.ibm.ws.runtime.component.DeployedApplicationImpl.fireDeployedObjectStart(DeployedApplicationImpl.java:1369)
at com.ibm.ws.runtime.component.DeployedModuleImpl.start(DeployedModuleImpl.java:638)
at com.ibm.ws.runtime.component.DeployedApplicationImpl.start(DeployedApplicationImpl.java:967)
at com.ibm.ws.runtime.component.ApplicationMgrImpl.startApplication(ApplicationMgrImpl.java:766)
at com.ibm.ws.runtime.component.ApplicationMgrImpl.startApplicationDynamically(ApplicationMgrImpl.java:1354)
at com.ibm.ws.runtime.component.ApplicationMgrImpl.start(ApplicationMgrImpl.java:2150)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.start(CompositionUnitMgrImpl.java:445)
at com.ibm.ws.runtime.component.CompositionUnitImpl.start(CompositionUnitImpl.java:123)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.start(CompositionUnitMgrImpl.java:388)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.access$500(CompositionUnitMgrImpl.java:116)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl$1.run(CompositionUnitMgrImpl.java:663)
at com.ibm.ws.security.auth.ContextManagerImpl.runAs(ContextManagerImpl.java:5413)
at com.ibm.ws.security.auth.ContextManagerImpl.runAsSystem(ContextManagerImpl.java:5539)
at com.ibm.ws.security.core.SecurityContext.runAsSystem(SecurityContext.java:255)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.startCompositionUnit(CompositionUnitMgrImpl.java:677)
at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.startCompositionUnit(CompositionUnitMgrImpl.java:621)
at com.ibm.ws.runtime.component.ApplicationMgrImpl.startApplication(ApplicationMgrImpl.java:1246)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:60)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
at java.lang.reflect.Method.invoke(Method.java:611)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:49)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:60)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
at java.lang.reflect.Method.invoke(Method.java:611)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:256)
at javax.management.modelmbean.RequiredModelMBean.invokeMethod(RequiredModelMBean.java:1085)
at javax.management.modelmbean.RequiredModelMBean.invoke(RequiredModelMBean.java:966)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:848)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:773)
at com.ibm.ws.management.AdminServiceImpl$1.run(AdminServiceImpl.java:1335)
at com.ibm.ws.security.util.AccessController.doPrivileged(AccessController.java:118)
at com.ibm.ws.management.AdminServiceImpl.invoke(AdminServiceImpl.java:1228)
at com.ibm.ws.management.commands.AdminServiceCommands$InvokeCmd.execute(AdminServiceCommands.java:251)
at com.ibm.ws.console.core.mbean.MBeanHelper.invoke(MBeanHelper.java:241)
at com.ibm.ws.console.appdeployment.ApplicationDeploymentCollectionAction.execute(ApplicationDeploymentCollectionAction.java:564)
at org.apache.struts.action.RequestProcessor.processActionPerform(Unknown Source)
at org.apache.struts.action.RequestProcessor.process(Unknown Source)
at org.apache.struts.action.ActionServlet.process(Unknown Source)
at org.apache.struts.action.ActionServlet.doPost(Unknown Source)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:595)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1214)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:774)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:456)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.invokeTarget(WebAppFilterChain.java:125)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:77)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:926)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1023)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java:1384)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:193)
at org.apache.struts.action.RequestProcessor.doForward(Unknown Source)
at org.apache.struts.tiles.TilesRequestProcessor.doForward(Unknown Source)
at org.apache.struts.action.RequestProcessor.processForwardConfig(Unknown Source)
at org.apache.struts.tiles.TilesRequestProcessor.processForwardConfig(Unknown Source)
at org.apache.struts.action.RequestProcessor.process(Unknown Source)
at org.apache.struts.action.ActionServlet.process(Unknown Source)
at org.apache.struts.action.ActionServlet.doPost(Unknown Source)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:595)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1214)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:774)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:456)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.invokeTarget(WebAppFilterChain.java:125)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:92)
at com.ibm.ws.console.core.servlet.WSCUrlFilter.setUpCommandAssistance(WSCUrlFilter.java:950)
at com.ibm.ws.console.core.servlet.WSCUrlFilter.continueStoringTaskState(WSCUrlFilter.java:499)
at com.ibm.ws.console.core.servlet.WSCUrlFilter.doFilter(WSCUrlFilter.java:320)
at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:192)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:89)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:926)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1023)
at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:87)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:895)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1662)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:195)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:452)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:511)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:305)
at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:83)
at com.ibm.ws.ssl.channel.impl.SSLReadServiceContext$SSLReadCompletedCallback.complete(SSLReadServiceContext.java:1784)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1659)