无法获取数据库元数据java.sql.SQLException：

Question

我正在使用hibernate sharedFactory进行数据库更新。 当我尝试进行一次更新时，我在日志中遇到以下错误：

2011-09-01 16:17:50,406 ERROR (org.hibernate.tool.hbm2ddl.SchemaUpdate:134:execute) - could not get database metadata
java.sql.SQLException: Connections could not be acquired from the underlying database!

2011-09-01 16:32:05,734 ERROR (org.hibernate.tool.hbm2ddl.SchemaUpdate:165:execute) - could not complete schema update
java.sql.SQLException: Connections could not be acquired from the underlying database!

这个例外恰恰就是抛出这行代码..

sessionFactoryShard = shardedConfig.buildShardedSessionFactory();

有人能说出这个错误发生的原因吗？