运行项目突然报了连接不上MySQL的错误，检查了数据库配置文件，没发现什么问题，经过排查，终于找到了错误原因，记录如下。

报错日志如下：

Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Access denied for user 'root'@'localhost' (using password: YES))
### The error may exist in com/javapandeng/mapper/ItemCategoryMapper.xml
### The error may involve com.javapandeng.mapper.ItemCategoryMapper.listBySqlReturnEntity
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Access denied for user 'root'@'localhost' (using password: YES))
	java.sql.SQLException: Access denied for user 'root'@'localhost' (using password: YES)
		at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
		at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
		at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
		at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:836)
		at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:456)
		at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)

 首先打开SQLyog，新建连接，输入本机localhost，数据库用户名密码，点击测试连接，发现数据库服务正常，用户名密码也正常。

 原因不在MySQL本身，再检查数据库配置文件，发现项目配置的properties文件中，数据库密码jdbc.password多了一个空格，导致报出密码错误的异常，去掉之后正常运行。

 需要免费永久版，可以搜索公众号"程序技术圈"，回复"SQLyog"获取，作为一个可视化工具，SQLyog还是非常方便的。