错误信息

警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@f84411 -- 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 (2). Last acquisition attempt exception: 
java.sql.SQLException: Access denied for user 'Li'@'localhost' (using password: YES)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:998)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3835)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3771)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:870)
    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1659)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1206)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2239)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2270)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2069)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:794)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.__newInstance(DelegatingConstructorAccessorImpl.java:45)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:389)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
    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)

在dataSource配置中数据库账号密码配置正确的情况下，如果名字是root，使用${username}配置连接池的user属性会出现密码错误的异常，解决方法是把${username}更改为"root"，可能是mybatis的内部结构对root敏感，所以我们直接写到这里，不用配置文件引用方式