1、Some projects cannot be imported because they already exist in the workspace
2、Some projects were hidden because they exist in the workspace directory
这种情况基本是以下错误操作造成：
1.手动删除本地磁盘下的工程目录
2.删除时，没有勾选Delete project contents on disk(cannot be undone)
以上2种操作，eclipse本身不会删除一些以 二进制形式记录的工程信息，
所以你在导入的时候就提示工程已经存在了~
有时候eclipse或者myeclipse导入项目的时候会发生上面两个错误，IDE不允许我们导入。具体原因是在IDE的workspace中已经存在了相同名字的项目，所以不能导入。
解决办法则是修改项目名：
1、right click【右键】 --- refactor --- rename
2、workspace中要修改名字的项目 --- 打开.project文件 --- 修改<name>projectName</name>【导出到myeclipse外面的项目不能通过直接改项目名称来修改真正的项目名称，只能通过这种方式】
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注意:诚然修改项目名可以解决，但是给人的感觉好像是以前的找不到了（工程目录下面明明没有）导致无法删除，只好改名，实乃无奈之举!!
思考--加入不进去，一定是以前的有一个标记记录了你的工程信息，也就是说找到那个标记删除它，我们就不用改名字了。经过我的摸索
E:workspaceeclipseworkspace.metadata.pluginsorg.eclipse.core.resources.projects 在我的这个版本的eclipse上是这个目录里面
警告：The file connot be validate as there was a connect problem
解决方式： 引入所需的dtd
ps：这种只是警告，不是错误，所以不处理也是没问题的，只是它不能出现提示而已。主要原因是这些dtd本来是可以通过网络获取的，假如你没有网络，它就没办法通过联网获得，所以解决办法就是把这些文件导入myeclipse。
错误：java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver
java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526) at org.apache.commons.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1420) at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371) at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044) at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111) at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77) at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:80) at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:66) at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:279) at org.apache.ibatis.executor.BatchExecutor.doQuery(BatchExecutor.java:80) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:267) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:141) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:98) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:73) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:101) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:95) 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.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:355) at $Proxy37.selectList(Unknown Source) at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:195) at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:120) at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:90) at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:40) at $Proxy42.selectTest(Unknown Source) at com.test.sevices.MonitorService.showModule(MonitorService.java:16) at com.test.controller.MonitorController.showModule(MonitorController.java:20) 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.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176) at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436) at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789) at javax.servlet.http.HttpServlet.service(HttpServlet.java:643) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:619)
报错原因：
缺失了连接oracle数据库的驱动文件
解决办法：
在MyEclipse中引入oracle 11g自带的jdbc包（如“G:appwelcomeproduct11.1.0db_1jdbclibojdbc6.jar”）：右击java项目，选择“Build Path”、“Configure Build Path”，单击“Add External JARs”按钮，选择你的ojdbc6.jar；