调试了一天，错误变成了这个

二月 29, 2016 4:03:02 下午 org.hibernate.annotations.common.Version <clinit>

INFO: HCANN000001: Hibernate Commons Annotations {4.0.2.Final}

二月 29, 2016 4:03:02 下午 org.hibernate.Version logVersion

INFO: HHH000412: Hibernate Core {4.2.4.Final}

二月 29, 2016 4:03:02 下午 org.hibernate.cfg.Environment <clinit>

INFO: HHH000206: hibernate.properties not found

二月 29, 2016 4:03:02 下午 org.hibernate.cfg.Environment buildBytecodeProvider

INFO: HHH000021: Bytecode provider name : javassist

二月 29, 2016 4:03:02 下午 org.hibernate.cfg.Configuration configure

INFO: HHH000043: Configuring from resource: /hibernate.cfg.xml

二月 29, 2016 4:03:02 下午 org.hibernate.cfg.Configuration getConfigurationInputStream

INFO: HHH000040: Configuration resource: /hibernate.cfg.xml

二月 29, 2016 4:03:03 下午 org.hibernate.cfg.Configuration addResource

INFO: HHH000221: Reading mappings from resource: Students.hbm.xml

二月 29, 2016 4:03:03 下午 org.hibernate.internal.util.xml.DTDEntityResolver resolveEntity

WARN: HHH000223: Recognized obsolete hibernate namespace http://hibernate.sourceforge.net/. Use namespace http://www.hibernate.org/dtd/ instead. Refer to Hibernate 3.6 Migration Guide!

二月 29, 2016 4:03:03 下午 org.hibernate.cfg.Configuration doConfigure

INFO: HHH000041: Configured SessionFactory: null

二月 29, 2016 4:03:03 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

INFO: HHH000402: Using Hibernate built-in connection pool (not for production use!)

二月 29, 2016 4:03:03 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

INFO: HHH000115: Hibernate connection pool size: 20

二月 29, 2016 4:03:03 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

INFO: HHH000006: Autocommit mode: false

二月 29, 2016 4:03:03 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc.mysql:///hibernate?useUnicode=true&characterEncoding=UTF-8]

二月 29, 2016 4:03:03 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure

INFO: HHH000046: Connection properties: {user=root, password=****}