[Spring] Spring JDBC连接不上的问题解决
在学习Spring JDBC的过程中，遇到如下问题。描述如下：
可以连接到 test 数据库和information_schema数据库（test和information_schema数据库为MySQL安装后本身就有的数据库），但是连接不上自己create的数据库。测试过程显示错误信息为：
警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@4b76c591 -- 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: Access denied for user 'arthur'@'localhost' (using password: YES) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3515) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3447) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:911) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3953) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1276) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2048) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:723) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46) at sun.reflect.GeneratedConstructorAccessor7.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:422) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282) 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.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
可以发现，该错误产生原因：账号密码的问题！但是注意！！！可以连接上 test数据库。
后来笔者经过测试，发现，只要密码为空，任意字符串的账号都可以访问test数据库，笔者认为这是MySQL不好的一个地方，仅供参考（因为我不能理解test数据库这样设置的缘由）。
笔者连接数据库采用的是c3p0连接池的方式，这里有个致命的错误。如下：
这是配置c3p0的bean。
<!-- 配置c3p0数据源 -->
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="user" value="${user}"></property>
<property name="password" value="${password}"></property>
<property name="jdbcUrl" value="${JdbcUrl}"></property>
<property name="driverClass" value="${driverClass}"></property>
<property name="numHelperThreads" value="10"></property>
<property name="initialPoolSize" value="${initPoolSize}"></property>
<property name="maxPoolSize" value="${maxPoolSize}"></property>
</bean>
<property name="user" value="${user}"></property>value="${user}"，注意！！！这里不能用user!!!改成
<property name="user" value="${username}"></property>问题解决，成功连接。
综上，该问题产生的原因是：变量名称可能会与系统或者框架中的变量产生冲突。所以在命名时，不要采用可能会冲突的名称。