各位大神，本人初次接触birt 报表系统，求指教，在ecliplse 中进行birt 报表开发，最后再点击预览的时候，系统突然提示了这么一个错，错误信息如下：
java.lang.NoClassDefFoundError: org/eclipse/jetty/util/Decorator
at org.eclipse.birt.report.viewer.utilities.ViewerWebApp.start(ViewerWebApp.java:40)
at org.eclipse.birt.report.viewer.utilities.AppServerWrapper.startJettyServer(AppServerWrapper.java:256)
at org.eclipse.birt.report.viewer.utilities.AppServerWrapper.start(AppServerWrapper.java:155)
at org.eclipse.birt.report.viewer.utilities.WebappAccessor.start(WebappAccessor.java:72)
at org.eclipse.birt.report.viewer.utilities.WebViewer.startWebApp(WebViewer.java:827)
at org.eclipse.birt.report.viewer.utilities.WebViewer.display(WebViewer.java:1078)
at org.eclipse.birt.report.viewer.utilities.WebViewer.display(WebViewer.java:1073)
at org.eclipse.birt.report.designer.ui.actions.PreviewSupport.preview(PreviewSupport.java:340)
at org.eclipse.birt.report.designer.ui.actions.PreviewToolbarMenuAction.run(PreviewToolbarMenuAction.java:75)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:250)
at org.eclipse.ui.internal.WWinPluginAction.runWithEvent(WWinPluginAction.java:230)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:568)
at org.eclipse.jface.action.ActionContributionItem.lambda$5(ActionContributionItem.java:439)
at org.eclipse.jface.action.ActionContributionItem$$Lambda$205/1190500337.handleEvent(Unknown Source)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4131)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1055)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3944)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3547)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1173)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1062)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:155)
at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:644)
at org.eclipse.ui.internal.Workbench$$Lambda$47/25136566.run(Unknown Source)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:566)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:155)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:137)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:107)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:400)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:661)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:597)
at org.eclipse.equinox.launcher.Main.run(Main.java:1476)
Caused by: java.lang.ClassNotFoundException: org.eclipse.jetty.util.Decorator cannot be found by org.eclipse.jetty.servlet_9.4.5.v20170502
at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:511)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:422)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:414)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:153)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 41 more
本人ecliplse 版本为最新版本2019-03 (4.11.0)，birt 报表版本为4.8.0，已经按照博客上面各种方法安装jetty插件，还是没什么效果，请各位大神指教。
