org.apache.ibatis.exceptions.PersistenceException解决办法

Caused by: org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
### The error may exist in file [D:\tomcat\apache-tomcat-8.0.20\webapps\JobSubmission2_war\WEB-INF\classes\mapper\StudentMapper.xml]
### The error may involve com.duowenjia.mapper.StudentMapper.studentLogin
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:122) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:113) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:73) ~[mybatis-3.3.0.jar:3.3.0]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:386) ~[mybatis-spring-1.2.3.jar:1.2.3]
... 49 common frames omitted
Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80) ~[spring-jdbc-4.1.7.RELEASE.jar:4.1.7.RELEASE]
at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:82) ~[mybatis-spring-1.2.3.jar:1.2.3]
at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:68) ~[mybatis-spring-1.2.3.jar:1.2.3]
at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:315) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:75) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:61) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:303) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:154) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:102) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:82) ~[mybatis-3.3.0.jar:3.3.0]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:120) ~[mybatis-3.3.0.jar:3.3.0]
... 56 common frames omitted

今天在使用ssm框架时出现了一个错误，之前都是好好的，突然出现了错误。

原因是在使用数据库管理工具的时候出现了太多的连接导致无法连接到数据库，解决方法是将Navicat中打开的表关闭即可。