使用浏览器访问项目时，出现异常：Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.itcast.dao.AccountDao.findAll'. It's likely that neither a Result Type nor a Result Map was specified.

浏览器报错：

Type 异常报告

消息 Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.itcast.dao.AccountDao.findAll'. It's likely that neither a Result Type nor a Result Map was specified.

描述 服务器遇到一个意外的情况，阻止它完成请求。

Exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.itcast.dao.AccountDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:986)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:870)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

Root Cause

org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.itcast.dao.AccountDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
    org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:79)
    org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:447)
    com.sun.proxy.$Proxy39.selectList(Unknown Source)
    org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:231)
    org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:137)
    org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:75)
    org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
    com.sun.proxy.$Proxy40.findAll(Unknown Source)
    cn.itcast.service.impl.AccountServiceImpl.findAll(AccountServiceImpl.java:20)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
　　 ...

Root Cause

org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.itcast.dao.AccountDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
	org.apache.ibatis.executor.resultset.DefaultResultSetHandler.validateResultMapsCount(DefaultResultSetHandler.java:287)
	org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:189)
	org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
	org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
	org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
	org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
　　　　　...

浏览器报此异常是因为使用mybatis访问数据库时对结果集进行封装出现异常，也就是说 mybatis 的mapper配置文件中对执行语句结果集的封装出现了问题。

需要查看mapper配置文件中执行语句的结果集，对其进行修改即可。