环境搭建失败，发送post的时候报以下错误，截取了前边的一些错误日志，老师帮忙看一下，是什么原因。
Sun Jul 09 21:16:41 CST 2017
HTTP/1.1 500 Internal Server Error
<html><head><title>Apache Tomcat/7.0.75 - Error report</title><style><!--H1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} H2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} H3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} BODY {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} B {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} P {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}A {color : black;}A.name {color : black;}HR {color : #525D76;}--></style> </head><body><h1>HTTP Status 500 - org.hibernate.exception.GenericJDBCException: Cannot open connection</h1><HR size="1" noshade="no shade"><p><b>type</b> Exception report</p><p><b>message</b> <u>org.hibernate.exception.GenericJDBCException: Cannot open connection</u></p><p><b>description</b> <u>The server encountered an internal error that prevented it from fulfilling this request.</u></p><p><b>exception</b> <pre>javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Cannot open connection
org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:614)
org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:202)
com.imooc.DAO.StudentDAO.findStudent(StudentDAO.java:27)
com.imooc.DAO.StudentDAO.find(StudentDAO.java:69)
com.imooc.service.StudentService.doPost(StudentService.java:69)
javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
