apollo-common/src/main/java/com/ctrip/framework/apollo/common/controller/WebMvcConfig.java/WebMvcConfig/customize
class WebMvcConfig:  @Override
  public void customize(TomcatServletWebServerFactory factory) {
    MimeMappings mappings = new MimeMappings(MimeMappings.DEFAULT);
    mappings.add("html", "text/html;charset=utf-8");
    factory.setMimeMappings(mappings );
  }