基于https://www.jianshu.com/p/b6932740f3c0来学习 Spring Boot开发，出现的问题记录如下：
1. 编译错误
Error:(32, 24) java: 不兼容的类型: java.lang.Long无法转换为com.yuqiyu.lessonthree.entity.UserEntity
userJPA.delete(id); 报错，
修改为
// userJPA.delete(id);
userJPA.deleteById(id);
2. 将application.yml的配置文件修改 application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/test?characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.jpa.show-sql=true
spring.jpa.database=mysql
3. Loading class `com.mysql.jdbc.Driver'. This is deprecated.
修改application.properties 中的 datasource.driver-class
#spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
4. 超时：
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
解决：
#spring.datasource.url=jdbc:mysql://localhost:3306/test?characterEncoding=utf8&useSSL=false
spring.datasource.url=jdbc:mysql://localhost:3306/test?characterEncoding=utf8&serverTimezone=UTC&autoReconnect=true
参考：https://www.cnblogs.com/chrischennx/p/7279215.html
5. 输入 http://localhost:8080/user/list， 无反馈。
java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
原因：Caused by: com.mysql.cj.exceptions.CJException: Unknown database
解决办法： 新建 test的 数据库文件，和对应的表格t_user
6： 执行 http://localhost:8080/user/save?name=admin&age=22&address=jinan, ， 无反馈。
原因：
Hibernate: select next_val as id_val from hibernate_sequence for update
2019-08-29 15:16:20.993 ERROR 5284 --- [nio-8080-exec-6] o.hibernate.id.enhanced.TableStructure : could not read a hi value
java.sql.SQLSyntaxErrorException: Table 'test.hibernate_sequence' doesn't exist
解决：
//@GeneratedValue
@GeneratedValue(strategy = GenerationType.IDENTITY)
参考：
https://www.cnblogs.com/app3306/p/9176575.html
7. 执行 http://localhost:8080/user/save?name=admin&age=22&address=jinan, ， 无反馈。
错误： java.sql.SQLException: Field 't_id' doesn't have a default value
解决：在mysql数据库中，如果自增长id没有设为Auto Increment，在java程序中就会报java.sql.SQLException: Field 'id' doesn't have a default value错误。
参考：
https://blog.csdn.net/xinghuo0007/article/details/51810867
http://www.programmersought.com/article/7674510934/