Could not open Hibernate Session for transaction

I am getting this error. please help me.

org.springframework.transaction.CannotCreateTransactionException: Could not open Hibernate Session for transaction; nested exception is org.hibernate.exception.GenericJDBCException: Cannot open connection
 org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:599)
 org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:374)
 org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:263)
 org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:101)
 org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
 org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
 $Proxy20.findFlierByID(Unknown Source)
 servlets.AwardServlet.doGet(AwardServlet.java:34)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

org.hibernate.exception.GenericJDBCException: Cannot open connection
 org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:126)
 org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:114)
 org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
 org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52)
 org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449)
 org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
 org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
 org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
 org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1354)
 org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:558)
 org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:374)
 org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:263)
 org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:101)
 org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
 org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
 $Proxy20.findFlierByID(Unknown Source)
 servlets.AwardServlet.doGet(AwardServlet.java:34)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1452)
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371)
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
 org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:82)
 org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
 org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
 org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
 org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
 org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1354)
 org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:558)
 org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:374)
 org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:263)
 org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:101)
 org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
 org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
 $Proxy20.findFlierByID(Unknown Source)
 servlets.AwardServlet.doGet(AwardServlet.java:34)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

java.lang.NullPointerException
 sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(Unknown Source)
 sun.jdbc.odbc.JdbcOdbcDriver.knownURL(Unknown Source)
 sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(Unknown Source)
 java.sql.DriverManager.getDriver(Unknown Source)
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1437)
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371)
 org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
 org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:82)
 org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
 org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
 org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
 org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
 org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1354)
 org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:558)
 org.springframework.transaction.support开发者_JAVA百科.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:374)
 org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:263)
 org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:101)
 org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
 org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
 $Proxy20.findFlierByID(Unknown Source)
 servlets.AwardServlet.doGet(AwardServlet.java:34)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

I have seen many examples on net but i could'nt solve this problem. so please help me.

I recently faced this issue. What i found out is that due to connection loss to the Database from application, this error pops up. There might be some operation that you are doing while DB is offline.

Please check your connection related parameters.

Hope this helps.