mysql 连接异常A ResourcePool could not acquire a resource from its primary factory or source.

java.sql.SQLException: Connections could not be acquired from the underlying database!
at com.jfinal.core.Config.startPlugins(Config.java:96)
at com.jfinal.core.Config.configJFinal(Config.java:48)
at com.jfinal.core.JFinal.init(JFinal.java:65)
at com.jfinal.core.JFinalFilter.init(JFinalFilter.java:49)
at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:277)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:258)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:382)
at org.apache.catalina.core.ApplicationFilterConfig.(ApplicationFilterConfig.java:103)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4650)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5306)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.jfinal.plugin.activerecord.ActiveRecordException: java.sql.SQLException: Connections could not be acquired from the underlying database!
at com.jfinal.plugin.activerecord.TableBuilder.build(TableBuilder.java:91)
at com.jfinal.plugin.activerecord.ActiveRecordPlugin.start(ActiveRecordPlugin.java:171)
at com.jfinal.core.Config.startPlugins(Config.java:87)
... 16 more
Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:529)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
at com.jfinal.plugin.activerecord.TableBuilder.build(TableBuilder.java:80)
... 18 more
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)
at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)

... 20 more

以上问题可能有一下原因造成：

1，驱动配置有误：driver=com.mysql.jdbc.Driver
2，数据库连接地址有误：url=jdbc:mysql://localhost:3306/test?3useUnicode=true&characterEncoding=utf8
3，密码或帐号有误：username=root
      password=root

4，数据库未启动或无权访问

5，项目未引入对应的驱动jar包mysql-connector-java-5.1.6-bin.jar

上面还解决不了，那就是驱动jar包版本问题