Spring Boot 的 web 场景自动引入了 json 场景：

    1. <dependency>
    2.   <groupId>org.springframework.boot</groupId>
    3.   <artifactId>spring-boot-starter-web</artifactId>
    4. </dependency>
    6. ->
    8. <dependency>
    9.   <groupId>org.springframework.boot</groupId>
    10.   <artifactId>spring-boot-starter-json</artifactId>
    11.   <version>2.3.4.RELEASE</version>
    12.   <scope>compile</scope>
    13. </dependency>