条件
数据库：sqlserver2017；
IDE：IDEA2017；
连接池：c3p0；
现象：
在启动tomcat时顺利进入启动页面，当开始进行登录或者有需要通过jdbc操作数据库时将报如下异常，并循环出现（说明页面请求不断的向jdbc发送但是就是找不到对应的入口）。
26-Dec-2019 17:21:30.868 [http-nio-8080-exec-10] com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getPoolManager Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hge9i0a7i6d4k21j2g57r|2875ba57, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.microsoft.sqlserver.jdbc.SQLServerDriver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge9i0a7i6d4k21j2g57r|2875ba57, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:sqlserver://localhost:1433; DatabaseName=ProspectHillMES1.0, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
26-Dec-2019 17:21:30.870 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded Could not load driverClass com.microsoft.sqlserver.jdbc.SQLServerDriver
java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1365)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:100)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:132)
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)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
26-Dec-2019 17:21:30.872 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2] com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded Could not load driverClass com.microsoft.sqlserver.jdbc.SQLServerDriver
java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1365)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:100)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:132)
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)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
26-Dec-2019 17:21:30.871 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1] com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded Could not load driverClass com.microsoft.sqlserver.jdbc.SQLServerDriver
java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1365)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:100)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:132)
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)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
26-Dec-2019 17:21:31.876 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded Could not load driverClass com.microsoft.sqlserver.jdbc.SQLServerDriver
java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1365)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.mchange.v2.c3p0.DriverManagerDataSource.ensureDriverLoaded(DriverManagerDataSource.java:100)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:132)
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)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
分析：
刚刚开始也不知道什么原因，通过异常的字面意思明白就是链接到数据库出现问题，这个现象其实也是非常常见的。
1.排查自己的jdbc配置看是否出现问题
<bean id="pooledDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="driverClass" value="com.microsoft.sqlserver.jdbc.SQLServerDriver">
</property>
<property name="jdbcUrl" value="jdbc:sqlserver://localhost:1433;DatabaseName=TEST"></property>
<property name="user" value="test"></property>
<property name="password" value="test"></property>
</bean>
2.在网上查询到说是“dbconfig.properties”文件中的空格导致，这对这个回答自己将文件中的内容重新审核一遍没有发现，并且将格式替换成 “步骤1”中的格式进行测试
jdbc.jdbcUrl=jdbc\:sqlserver\://127.0.0.1\:1433;DatabaseName\=TEST
jdbc.driverClass=com.microsoft.sqlserver.jdbc.SQLServerDriver
jdbc.user=test
jdbc.password=test
3.后续又想到是不是版本的问题，因为之前的项目是sqlserver2012，现在替换成为2017，可能JDBC驱动有升级于是将“pom.xml”文件的中jdbc驱动注释掉，重新从官网下载了一个全新的驱动，直接放置在web项目的"WEB-INF/lib"目录下通过“Project Structure/libraries”添加到lib库中，重新运行项目，成功进行数据库数据操作。
关于sqlserver2017jdbc驱动的更新方式可以参考该链接地址的博客：
https://blog.csdn.net/yogima/article/details/80614575
来源：CSDN
作者：Eggsy.Li
链接：https://blog.csdn.net/qq_19331985/article/details/103719430