Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'criticalService': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'criticalDao' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/com/unionx/api/dao/CriticalDao.class]: Cannot resolve reference to bean 'sqlSessionFactory' while setting bean property 'sqlSessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Invocation of init method failed; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'criticalDao' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/com/unionx/api/dao/CriticalDao.class]: Cannot resolve reference to bean 'sqlSessionFactory' while setting bean property 'sqlSessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Invocation of init method failed; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Invocation of init method failed; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in URL [jar:file:/opt/ylbs/bigdata-his-api/bigdata-his-api-1.0.jar!/ApplicationContext-mysql.xml]: Invocation of init method failed; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
Caused by: java.net.ConnectException: 连接超时
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

原因分析1

当数据库重启或数据库空闲连接超过设置的最大timemout时间，数据库会强行断开已有的链接，最大timeout时间可以通过命令show global variables like "wait_timeout";查询：

mysql> show global variables like "wait_timeout";
+---------------+-------+
| VARIABLE_NAME | VALUE |
+---------------+-------+
| wait_timeout  | 28800 |
+---------------+-------+
1 row in set (0.00 sec)

解决办法1

为了解决这个异常，我们在配置数据库连接池的时候需要做一些检查连接有效性的配置，这里以Druid为例，相关配置如下（更多配置）：
| 字段名 | 默认值 | 说明 |
| ----------------------------- | ----------- | ---------------------------------------- |
| validationQuery | | 用来检测连接是否有效的sql，要求是一个查询语句，常用select 'x'。如果validationQuery为null，testOnBorrow、testOnReturn、testWhileIdle都不会起作用。 |
| validationQueryTimeout | | 单位：秒，检测连接是否有效的超时时间。底层调用jdbc Statement对象的void setQueryTimeout(int seconds)方法 |
| testOnBorrow | true | 申请连接时执行validationQuery检测连接是否有效，做了这个配置会降低性能。 |
| testOnReturn | false | 归还连接时执行validationQuery检测连接是否有效，做了这个配置会降低性能。 |
| testWhileIdle | false | 建议配置为true，不影响性能，并且保证安全性。申请连接的时候检测，如果空闲时间大于timeBetweenEvictionRunsMillis，执行validationQuery检测连接是否有效。 |
| timeBetweenEvictionRunsMillis | 1分钟（1.0.14） | 有两个含义：1) Destroy线程会检测连接的间隔时间，如果连接空闲时间大于等于minEvictableIdleTimeMillis则关闭物理连接。2) testWhileIdle的判断依据，详细看testWhileIdle属性的说明 |

为了避免空闲时间过长超过最大空闲时间而被断开，我们设置三个配置：

validationQuery: SELECT 1
testWhileIdle: true
timeBetweenEvictionRunsMillis: 28000

其中timeBetweenEvictionRunsMillis需要小于mysql的wait_timeout。

但是这种方法无法避免重启的情况，不过一般数据库不会频繁重启，影响不大，如果非得频繁重启，可以通过设置testOnBorrow，即申请连接的时候先试一试连接是否可用，不过带来的影响就是性能降低，需要根据实际需求合理取舍。

原因分析2

解决办法2

执行set global interactive_timeout=604800;来设置 

3.重启 service mysqld restart

原因分析3

Error creating bean with name XXX

解决办法3

最后

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