[com.mysql.jdbc.Driver]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [com.mysql.jdbc.Driver]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1295) at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1283) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1148) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1109) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:348) at java.sql.DriverManager.isDriverAllowed(DriverManager.java:556) at java.sql.DriverManager.isDriverAllowed(DriverManager.java:548) at java.sql.DriverManager.getDriver(DriverManager.java:297) at com.mchange.v2.c3p0.DriverManagerDataSource.driver(DriverManagerDataSource.java:223) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool 1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)atcom.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)atcom.mchange.v2.resourcepool.BasicResourcePool.access 800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
tomcat服务器已断开，需要重启tomcat服务器，重新获得数据库连接池，在IDEA中要restart server 一配置的tomcat，不能只redelopy。建议更改Servlet后就restart server。
