jetty7 启动时报错…… 400 请求报错 

现使用jetty 7开发项目，使用myeclipse 8，已经配置好了jetty的路径，不部署项目时启动没有问题，当我部署项目后，启动时就报这个项目中缺少class文件，报错如下：  这个是什么原因呢，是因为我使用jetty有问题还是缺什么jar没有放到项目中呢，而这个jar又在哪里下载呢？

java.lang.ClassNotFoundException: org.eclipse.jetty.plus.webapp.Configuration at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at org.eclipse.jetty.util.Loader.loadClass(Loader.java:96) at org.eclipse.jetty.util.Loader.loadClass(Loader.java:75) at org.eclipse.jetty.webapp.WebAppContext.loadConfigurations(WebAppContext.java:840) at org.eclipse.jetty.webapp.WebAppContext.preConfigure(WebAppContext.java:405) at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:474) at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) at org.eclipse.jetty.deploy.bindings.StandardStarter.processBinding(StandardStarter.java:36) at org.eclipse.jetty.deploy.AppLifeCycle.runBindings(AppLifeCycle.java:183) at org.eclipse.jetty.deploy.DeploymentManager.requestAppGoal(DeploymentManager.java:491) at org.eclipse.jetty.deploy.DeploymentManager.addApp(DeploymentManager.java:138) at org.eclipse.jetty.deploy.providers.ScanningAppProvider.fileAdded(ScanningAppProvider.java:142) at org.eclipse.jetty.deploy.providers.ScanningAppProvider$1.fileAdded(ScanningAppProvider.java:53) at org.eclipse.jetty.util.Scanner.reportAddition(Scanner.java:604) at org.eclipse.jetty.util.Scanner.reportDifferences(Scanner.java:535) at org.eclipse.jetty.util.Scanner.scan(Scanner.java:398) at org.eclipse.jetty.util.Scanner.doStart(Scanner.java:332) at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) at org.eclipse.jetty.deploy.providers.ScanningAppProvider.doStart(ScanningAppProvider.java:118) at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) at org.eclipse.jetty.deploy.DeploymentManager.startAppProvider(DeploymentManager.java:552) at org.eclipse.jetty.deploy.DeploymentManager.doStart(DeploymentManager.java:227) at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) at org.eclipse.jetty.util.component.AggregateLifeCycle.doStart(AggregateLifeCycle.java:75) at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:53) at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:91) at org.eclipse.jetty.server.Server.doStart(Server.java:270) at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) at org.eclipse.jetty.xml.XmlConfiguration$1.run(XmlConfiguration.java:1260) at java.security.AccessController.doPrivileged(Native Method) at org.eclipse.jetty.xml.XmlConfiguration.main(XmlConfiguration.java:1183) 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.jetty.start.Main.invokeMain(Main.java:462) at org.eclipse.jetty.start.Main.start(Main.java:610) at org.eclipse.jetty.start.Main.main(Main.java:86)