postGis是pg库中计算地理信息的函数。

引入Maven依赖

     <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>

Pg库中安装postGis插件

如果你到这一步你就在mapper中直接使用postgis函数的话，你会发现一堆报错信息，都是找不到相应的函数

Cause: org.postgresql.util.PSQLException: ERROR: function st_geographyfromtext(unknown) does not exist
  建议：No function matches the given name and argument types. You might need to add explicit type casts.
  位置：151
; bad SQL grammar []; nested exception is org.postgresql.util.PSQLException: ERROR: function st_geographyfromtext(unknown) does not exist
  建议：No function matches the given name and argument types. You might need to add explicit type casts.
  位置：151] with root cause

org.postgresql.util.PSQLException: ERROR: function st_geographyfromtext(unknown) does not exist
  建议：No function matches the given name and argument types. You might need to add explicit type casts.

解决办法：将pg库的连接地址后面加上public，代表这个库是公共的，所有的函数都可以使用