SpringBoot 2.2.5 cannot automatically inject RestTemplate

• Stray information

Consider defining a bean of type 'org.springframework.web.client.RestTemplate' 
in your configuration.
No qualifying bean of type [org.springframework.web.client.RestTemplate] found

• the reason

Spring Boot<=1.3 无需定义，Spring Boot自动为您定义了一个。
 
Spring Boot >= 1.4 Spring Boot不再自动定义一个RestTemplate，
  而是定义了一个RestTemplateBuilder允许您更好地控制所RestTemplate创建的对象

• solution

    Define RestTemplate Bean to complete the injection

@Configuration
public class RestTemplateConfig {

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder){
        return builder.build();
    }
}