如果你是类似下面的2点配置
1.jdbc.properties文件
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/o2o?characterEncoding=utf8
jdbc.username=root
jdbc.password=****
2.POM文件
<!-- mysql数据库连接包-->
<!--这个jar包版本如果是8.0.12，则会报错-->
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.12</version>
</dependency>
<!-- 数据源c3p0 -->
<!-- https://mvnrepository.com/artifact/com.mchange/c3p0 -->
<dependency>
<groupId>com.mchange</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.5.2</version>
</dependency>
看到如下红色字体错误：
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
你会去将jdbc.driver=com.mysql.jdbc.Driver改成jdbc.driver=com.mysql.jdbc.cj.Driver
结果又会报如下红色字体错误
org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
### The error may exist in file [D:\SSM_maven\o2o\target\classes\mapper\AreaDao.xml]
### The error may involve com.imooc.o2o.dao.AreaDao.queryArea
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
我当初就是遇到了这样的问题，查了很多的方法，都没能解决，但最后还是死马当活马医，做了如下改动，就解决了问题，还一脸懵逼，怎么会是这个原因呀！
解决方法很简单，如下：
1.降低 mysql-connector-java的jar包版本，比如降为如下
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
运行后再报如下错误
WARN com.mchange.v2.c3p0.DriverManagerDataSource - Could not load driverClass com.mysql.jdbc.cj.Driver
java.lang.ClassNotFoundException: com.mysql.jdbc.cj.Driver
2.根据上面错误提示，很容易想到修改jdbc.properties,其实也就是还原最初的样子,如下
jdbc.driver=com.mysql.jdbc.Driver
3.再运行，OK
最后，总结如下：
<!-- mysql数据库连接包-->
<!--这个jar包版本如果是6.x.x及以上，则会报错，所以改成5.x.x-->
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
</dependency>
<!-- 数据源c3p0 -->
<!-- https://mvnrepository.com/artifact/com.mchange/c3p0 -->
<dependency>
<groupId>com.mchange</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.5.2</version>
</dependency>
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