MyBatis入门踩坑记录

问题说明

学习过程中遇到很多问题，记录一下。

Maven静态资源过滤问题

<!--在build中配置resource，来防止我们资源导出失败的问题--><build><resources><resource><directory>src/main/java</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>false</filtering></resource><resource><directory>src/main/resources</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>false</filtering></resource></resources></build>

Junit测试时，可能会提示

org.apache.ibatis.binding.BindingException: Type interface com.melodyhub.dao.UserDao is not known to the MapperRegistry.

MapperRegistry是什么？

每一个Mapper.xml都需要在MyBatis核心配置文件中注册！！！

<!--每一个Mapper.xml都需要在MyBatis核心配置文件中注册！！！--><mappers>	<!--<mapper class="com.melodyhub.dao.UserMapper"/>-->	<mapper resource="com/melodyhub/dao/UserMapper.xml"/></mappers>

MySQL时区

由于MySQL底层是使用的时区是CST，跟中国时间相差挣好8个小时。

解决办法是在mybatis-config.xml中``jdbc的url`末尾加上，二选一即可：

&serverTimezone=GMT%2B8&useTimezone=true&serverTimezone=UTC

参考：https://blog.csdn.net/ziningyihao/article/details/90644295

MySQL驱动/版本问题

所有的代码都没有问题，但是就是连接不上数据库，经过排查，发现我的MySQL版本是8.0，驱动包是5.1.47，差距太大，不兼容。

将MySQL降级到5.7.29，问题解决。

解决Mybatis报错Could not find resource mybatis-config.xml

下午移植远程仓库项目的时候，控制台报错：

java.io.IOException: Could not find resource mybatis-config.xml

经过排查，发现是我没有一直夫工程的pom.xml文件。

Maven clean清除缓存，然后build，即可。

-解决Mybatis报错Could not find resource mybatis-config.xml

MyBatis问题解决Error building SqlSession.

解决🐤

改为全类名：com.melodyhub.pojo.User

MyBatis问题解决Error building SqlSession.

连接JDBC报错:com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.

问题：
Spring整合Mybatis时候，出现数据库连接异常：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.

分析：

找了好半天的原因，最后发现是相关jdbc驱动包版本太低！

解决方法：

下载最新版的mysql-connector-java即可。
虽然可以连接成功，但是控制台还是提示：

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.

修改一下mybatis-config.xml：

<!--<property name="driver" value="com.mysql.jdbc.Driver"/>--><property name="driver" value="com.mysql.cj.jdbc.Driver"/>

mysql 连接池连接超时的问题(The last packet successfully received from the server was 2,431 milliseconds ago. The last packet sent successfully to the server was 2,417 milliseconds ago.)

org.apache.ibatis.exceptions.PersistenceException: ### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet successfully received from the server was 2,431 milliseconds ago.  The last packet sent successfully to the server was 2,417 milliseconds ago.### The error may exist in com/melodyhub/mapper/UserMapper.xml### The error may involve com.melodyhub.mapper.UserMapper.selectUser### The error occurred while executing a query### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet successfully received from the server was 2,431 milliseconds ago.  The last packet sent successfully to the server was 2,417 milliseconds ago.	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:149)	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)	

解决：
是mysql超时设置的问题
如果连接闲置8小时 (8小时内没有进行数据库操作), mysql就会自动断开连接。

在connection url中加参数: autoReconnect=true

jdbc.url=jdbc:mysql://localhost:3306/database?autoReconnect=true&autoReconnectForPools=true