Failed to configure a DataSource: ‘url’ attribute is not specified and no embedded datasource could be configured
spring boot需要配置好datasource才可以正常运行，在properties中
spring.datasource.url=jdbc:mysql://localhost:3306/mysql
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
@RestController
这个标签是@Controller 和@ResponseBody的组合
如果遇到8080端口被占用，The Tomcat connector configured to listen on port 8080 failed to start intellij idea
1 netstat -ao |find /i “listening”，查看8080端口被哪个进程占用
TCP 0.0.0.0:7981 machinename:0 LISTENING 2428
TCP 0.0.0.0:7982 machinename:0 LISTENING 2428
TCP 0.0.0.0:8080 machinename:0 LISTENING 12704
TCP 0.0.0.0:8500 machinename:0 LISTENING 2428
2 Taskkill /F /IM 12704 (Note: Mention correct Process Id)，杀掉此进程
