1.初学java链接数据库，出现

com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@3f72acc1 --
Acquisition Attempt Failed!!! Clearing pending acquires.

While trying to acquire a needed new resource, we failed to succeed more than   
the maximum number of allowed acquisition attempts (30). Last acquisition 
attempt exception:   

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

怀疑是数据库没链接成功！
查看eclispe端口号为3306，于是查看mysql的端口号，终端输入：

show global variables like 'port';

后显示：

image.png

果然不是3306 于是决定修改方法为

1.停止MySQL服务
2.在com.oracle.oss.mysql.mysqld.plist文件中的ProgramArguments下添加<string>--port=3306</string>保存退出
这里直接修改可能会提示没有权限
3.打开终端输入cd 到com.oracle.oss.mysql.mysqld.plist所在目录
输入

sudo vim  com.oracle.oss.mysql.mysqld.plist

编辑为如下图

image.png

保存
重启mysql