eclipse经常提示空指针异常

各位高手，help.
问题如下：
本人的eclipse时不时会出现空指针异常，还有就是，如下图这种情况，

eclipse工作空间中的.metadata的log日志文件，会出现如下异常：
!ENTRY org.eclipse.jface 4 2 2015-01-09 10:28:34.898
!MESSAGE Problems occurred when invoking code from plug-in: “org.eclipse.jface”.
!STACK 0
java.lang.NullPointerException
at org.eclipse.jst.jee.ui.internal.navigator.web.WebAppProvider.getImage(WebAppProvider.java:99)
at org.eclipse.jst.jee.ui.internal.navigator.Web25LabelProvider.getImage(Web25LabelProvider.java:47)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceLabelProvider.findImage(NavigatorContentServiceLabelProvider.java:197)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceLabelProvider.getColumnImage(NavigatorContentServiceLabelProvider.java:105)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceLabelProvider.getImage(NavigatorContentServiceLabelProvider.java:98)
at org.eclipse.ui.internal.navigator.NavigatorDecoratingLabelProvider$StyledLabelProviderAdapter.getImage(NavigatorDecoratingLabelProvider.java:59)
at org.eclipse.jface.viewers.DelegatingStyledCellLabelProvider.getImage(DelegatingStyledCellLabelProvider.java:195)
at org.eclipse.jface.viewers.DecoratingStyledCellLabelProvider.getImage(DecoratingStyledCellLabelProvider.java:173)
at org.eclipse.ui.navigator.CommonNavigatorManager.updateStatusBar(CommonNavigatorManager.java:308)
at org.eclipse.ui.navigator.CommonNavigatorManager$1.selectionChanged(CommonNavigatorManager.java:74)
at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:876)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:178)
at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:873)
at org.eclipse.jface.viewers.StructuredViewer.handlePostSelect(StructuredViewer.java:1217)
at org.eclipse.ui.navigator.CommonViewer.handlePostSelect(CommonViewer.java:470)
at org.eclipse.jface.viewers.StructuredViewer$5.widgetSelected(StructuredViewer.java:1243)
at org.eclipse.jface.util.OpenStrategy.firePostSelectionEvent(OpenStrategy.java:265)
at org.eclipse.jface.util.OpenStrategy.access$5(OpenStrategy.java:259)
at org.eclipse.jface.util.OpenStrategy$1$2.run(OpenStrategy.java:440)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:136)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4147)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3764)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1151)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1032)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:148)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:636)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:579)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:135)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:648)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:603)
at org.eclipse.equinox.launcher.Main.run(Main.java:1465)
但是org.eclipse.jface这个插件不是eclipse自身自带的吗？为什么会这样？本人不知道怎么解决，eclipse本人已经换了多次，工作空间本人也换了多次，可是问题还是依旧。help