Junit测试的时候连接数据库成功，能添加记录
但是启动服务器通过表单提交到servlet，连接数据库失败
报错如下:
十二月 11, 2018 4:35:48 下午 com.mchange.v2.c3p0.DriverManagerDataSource ensureDriverLoaded
警告: Could not load driverClass com.mysql.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.jdbc.Driverat org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1275)at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1104)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.ThreadPerTaskAsynchronousRunner$TaskThread.run(ThreadPerTaskAsynchronousRunner.java:255)十二月 11, 2018 4:35:48 下午 com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask run
警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@5361e6f4 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
java.sql.SQLException: No suitable driverat java.sql.DriverManager.getDriver(DriverManager.java:315)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)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.ThreadPerTaskAsynchronousRunner$TaskThread.run(ThreadPerTaskAsynchronousRunner.java:255)项目结构如下图
注意:图上的web.xml放错位置了，正常是在WE-INF目录下的。初学弄错了，放在lib目录下了。
原因:该项目是一个web项目，而且这个mysql-connector-java-5.1.12-bin.jar位置不再项目内，只是引用了本地的jar，junit测试时类加载器找的是本地的jar包，所以能找到这个jar包。但是web项目它最终不是通过本地的JRE去运行，而是部署到web 服务器，如Tomcat、Weblogic、WebSphere等，这些服务器都实现了自身的类加载器。比如tomcat应用服务器,它有其自己的类加载器,根据J2EE的规范去%web-project%/WEB-INF/lib的规范去找相应的lib 。所以在服务器上运行时找不到mysql-connector-java-5.1.12-bin.jar，连接数据库失败。
解决方案:将mysql-connector-java-5.1.12-bin.jar包copy到web-inf/lib文件夹下面，然后build path即可。
