解決：CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.

log4j給出的異常信息有下面幾句：

Caused by: org.hibernate.exception.GenericJDBCException: Unable to acquire JDBC Connection
	at ...
Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
	at ...
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
	at ...

多半是關於數據庫的配置有問題

剛開始網上查了很多資料還是百思不得其解，從 pom 中把log4j，slf4j-api，slf4j-log4j12等依賴去掉（從log4j切換成了默認日志），才看到下面這個異常信息，這才明白是url里需要加上時區參數。

四月 16, 2020 8:36:09 下午 com.mchange.v2.log.MLog <clinit>
信息: MLog clients using java 1.4+ standard logging.
...
java.sql.SQLException: The server time zone value '�й���׼ʱ��' is unrecognized or represents more than one time zone.

關於數據庫配置的幾個建議：

• 用mysql-connector-java-8.x.x-bin.jar的驅動com.mysql.cj.jdbc.Driver連接MySQL 8；
• URL 最好帶上characterEncoding和serverTimezone，還可以指明是否進行SSL連接useSSL=false：（XML文件 記得用&來轉義&）

/// xml 文件
<property name="jdbcUrl" value="jdbc:mysql://localhost:3306/test?useSSL=false&amp;characterEncoding=utf8&amp;serverTimezone=UTC"/>

/// properties 文件
jdbc.url=jdbc:mysql://localhost:3306/test?useSSL=false&characterEncoding=utf8&serverTimezone=UTC