at comalibabadruidpoolDruidPooledPreparedStatementexecuteQueryDruidPooledPreparedStatementjava227 at comxjadaoimplUserDaoImplqueryUserByUnameAndPwdUserDaoImpljava30 at comxjaserviceimplUserServiceImpl

在com.alibaba.druid.pool.DruidPooledPreparedStatement.executeQuery(DruidPooledPreparedStatement.java:227)处发生了异常，导致com.xja.dao.impl.UserDaoImpl.queryUserByUnameAndPwd(UserDaoImpl.java:30)、com.xja.service.impl.UserServiceImpl.queryUserByUnameAndPwd(UserServiceImpl.java:16)和com.xja.servlet.LoginServlet.doGet(LoginServlet.java:34)等方法出现问题。具体原因可能与数据库访问或SQL语句有关。