求javaWeb大神，一个异常问题，特别奇怪。。。。。?报错

我昨天运行项目的时候一切都正常，可以运行，什么都正常的不得了，可是今天早上又运行的时候突然就报出如下错误：

严重: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'checkBtrName': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.CannotLoadBeanClassException: Error loading class [com.explorer.sps.service.impl.UserServiceImpl] for bean with name 'userService' defined in file [D:\apache-tomcat-7.0.42\webapps\StraightPinSystem\WEB-INF\classes\com\explorer\sps\service\impl\UserServiceImpl.class]: problem with class file or dependent class; nested exception is java.lang.UnsupportedClassVersionError: com/explorer/sps/service/impl/UserServiceImpl : Unsupported major.minor version 51.0 (unable to load class com.explorer.sps.service.impl.UserServiceImpl)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:300)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1055)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:511)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:562)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:871)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:423)
at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:272)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:196)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4939)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5434)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1113)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1671)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.springframework.beans.factory.CannotLoadBeanClassException: Error loading class [com.explorer.sps.service.impl.UserServiceImpl] for bean with name 'userService' defined in file [D:\apache-tomcat-7.0.42\webapps\StraightPinSystem\WEB-INF\classes\com\explorer\sps\service\impl\UserServiceImpl.class]: problem with class file or dependent class; nested exception is java.lang.UnsupportedClassVersionError: com/explorer/sps/service/impl/UserServiceImpl : Unsupported major.minor version 51.0 (unable to load class com.explorer.sps.service.impl.UserServiceImpl)
at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1211)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:427)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:435)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:409)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:541)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:159)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:84)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:297)
... 27 more
Caused by: java.lang.UnsupportedClassVersionError: com/explorer/sps/service/impl/UserServiceImpl : Unsupported major.minor version 51.0 (unable to load class com.explorer.sps.service.impl.UserServiceImpl)
at org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:2899)
at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:1173)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1681)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
at org.springframework.util.ClassUtils.forName(ClassUtils.java:258)
at org.springframework.beans.factory.support.AbstractBeanDefinition.resolveBeanClass(AbstractBeanDefinition.java:408)
at org.springframework.beans.factory.support.AbstractBeanFactory.doResolveBeanClass(AbstractBeanFactory.java:1229)
at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1200)
... 38 more