java.lang.NullPointerException
at org.eclipse.m2e.jdt.internal.MavenClasspathContainerInitializer.initialize(MavenClasspathContainerInitializer.java:48)
at org.eclipse.jdt.internal.core.JavaModelManager.initializeContainer(JavaModelManager.java:2707)
at org.eclipse.jdt.internal.core.JavaModelManager$11.run(JavaModelManager.java:2613)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
at org.eclipse.jdt.internal.core.JavaModelManager.initializeAllContainers(JavaModelManager.java:2653)
at org.eclipse.jdt.internal.core.JavaModelManager.getClasspathContainer(JavaModelManager.java:1845)
at org.eclipse.jdt.core.JavaCore.getClasspathContainer(JavaCore.java:2705)
at org.eclipse.jdt.internal.core.JavaProject.resolveClasspath(JavaProject.java:2645)
at org.eclipse.jdt.internal.core.JavaProject.resolveClasspath(JavaProject.java:2783)
at org.eclipse.jdt.internal.core.JavaProject.getResolvedClasspath(JavaProject.java:1915)
at org.eclipse.jdt.internal.core.JavaProject.getClasspathEntryFor(JavaProject.java:1403)
at org.eclipse.jdt.internal.core.JavaModelManager.createJarPackageFragmentRootFrom(JavaModelManager.java:975)
at org.eclipse.jdt.internal.core.JavaModelManager.create(JavaModelManager.java:866)
at org.eclipse.jdt.internal.core.JavaModelManager.create(JavaModelManager.java:827)
at org.eclipse.jdt.core.JavaCore.create(JavaCore.java:2590)
at org.eclipse.jdt.internal.ui.ResourceAdapterFactory.getAdapter(ResourceAdapterFactory.java:44)
at org.eclipse.core.internal.adapter.AdapterFactoryProxy.getAdapter(AdapterFactoryProxy.java:80)
at org.eclipse.core.internal.runtime.AdapterManager.getAdapter(AdapterManager.java:295)
at org.eclipse.core.runtime.PlatformObject.getAdapter(PlatformObject.java:66)
at org.eclipse.jdt.internal.ui.EditorInputAdapterFactory.getAdapter(EditorInputAdapterFactory.java:53)
at org.eclipse.core.internal.adapter.AdapterFactoryProxy.getAdapter(AdapterFactoryProxy.java:80)
at org.eclipse.core.internal.runtime.AdapterManager.getAdapter(AdapterManager.java:295)
at org.eclipse.core.runtime.PlatformObject.getAdapter(PlatformObject.java:66)
at org.eclipse.ui.part.FileEditorInput.getAdapter(FileEditorInput.java:263)
at org.eclipse.jdt.ui.JavaUI.getEditorInputJavaElement(JavaUI.java:753)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.getInputFromEditor(PackageExplorerPart.java:1005)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.editorActivated(PackageExplorerPart.java:995)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.setLinkingEnabled(PackageExplorerPart.java:1271)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.createPartControl(PackageExplorerPart.java:548)
at org.eclipse.ui.internal.ViewReference.createPartHelper(ViewReference.java:375)
at org.eclipse.ui.internal.ViewReference.createPart(ViewReference.java:229)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
at org.eclipse.ui.internal.PartPane.setVisible(PartPane.java:313)
at org.eclipse.ui.internal.ViewPane.setVisible(ViewPane.java:529)
at org.eclipse.ui.internal.presentations.PresentablePart.setVisible(PresentablePart.java:180)
at org.eclipse.ui.internal.presentations.util.PresentablePartFolder.select(PresentablePartFolder.java:270)
at org.eclipse.ui.internal.presentations.util.LeftToRightTabOrder.select(LeftToRightTabOrder.java:65)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation.selectPart(TabbedStackPresentation.java:473)
at org.eclipse.ui.internal.PartStack.refreshPresentationSelection(PartStack.java:1254)
at org.eclipse.ui.internal.PartStack.setSelection(PartStack.java:1207)
at org.eclipse.ui.internal.PartStack.showPart(PartStack.java:1606)
at org.eclipse.ui.internal.PartStack.replace(PartStack.java:914)
at org.eclipse.ui.internal.PerspectiveHelper.addPart(PerspectiveHelper.java:400)
at org.eclipse.ui.internal.Perspective.removeFastView(Perspective.java:1192)
at org.eclipse.ui.internal.Perspective.removeFastView(Perspective.java:1167)
at org.eclipse.ui.internal.WorkbenchPage.removeFastView(WorkbenchPage.java:2988)
at org.eclipse.ui.internal.FastViewManager.makeFast(FastViewManager.java:380)
at org.eclipse.ui.internal.FastViewManager.removeViewReference(FastViewManager.java:360)
at org.eclipse.ui.internal.FastViewManager.restoreToPresentation(FastViewManager.java:665)
at org.eclipse.ui.internal.ViewStack.setMinimized(ViewStack.java:155)
at org.eclipse.ui.internal.PartStack.smartUnzoom(PartStack.java:1422)
at org.eclipse.ui.internal.PartStack$3.runWithException(PartStack.java:1478)
at org.eclipse.ui.internal.StartupThreading$StartupRunnable.run(StartupThreading.java:31)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:179)
at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:150)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4584)
at org.eclipse.ui.internal.StartupThreading.runWithoutExceptions(StartupThreading.java:94)
at org.eclipse.ui.internal.PartStack.setState(PartStack.java:1471)
at org.eclipse.ui.internal.PartStack$1.setState(PartStack.java:145)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation$1.handleEvent(TabbedStackPresentation.java:76)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:269)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:274)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.handleDoubleClick(AbstractTabFolder.java:353)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder$3.mouseDoubleClick(AbstractTabFolder.java:89)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:189)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4066)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3657)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2640)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2604)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2438)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:671)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:664)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:115)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:369)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:619)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:574)
at org.eclipse.equinox.launcher.Main.run(Main.java:1407)
关掉package explorer，再打开这个视图又好了。
从上述代码中，可以一窥eclipse的原理。