Servlets 找不到适合jdbc的驱动程序：mysql://localhost/circuit 使用C3P0PooledConnectionPool

您好，我使用的是C3P0连接池，我发现此错误是间歇性的：

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost/circuit
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:66)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:76)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1.acquireResource(C3P0PooledConnectionPool.java:66)
    at com.mchange.v2.resourcepool.BasicResourcePool.assimilateResource(BasicResourcePool.java:787)
    at com.mchange.v2.resourcepool.BasicResourcePool.acquireUntil(BasicResourcePool.java:548)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$000(BasicResourcePool.java:35)
    at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:972)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:148)

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有什么线索吗？

没有找到适合jdbc的驱动程序：mysql://localhost/circuit. JDBC驱动程序应该出现在类路径上，但实际上不是。我的lib文件夹中有com.mysql.JDBC_5.1.5.jar。那么还需要做什么呢？如果您显示了可能认为是此异常原因的代码，有人可能会对此有所了解。我是否应该显示正在进行DB调用的代码或连接的配置？