jackson-dataformat-xml引入使用后，响应体全是xml

解决方案：

https://spring.io/blog/2013/05/11/content-negotiation-using-spring-mvc

import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {/***  Total customization - see below for explanation.*/@Overridepublic void configureContentNegotiation(ContentNegotiationConfigurer configurer) {configurer.favorPathExtension(false).favorParameter(true).parameterName("mediaType").ignoreAcceptHeader(true).useJaf(false).defaultContentType(MediaType.APPLICATION_JSON).mediaType("xml", MediaType.APPLICATION_XML).mediaType("json", MediaType.APPLICATION_JSON);}
}