Add this on your spring boot project:

@Bean
@Order(Ordered.HIGHEST_PRECEDENCE)
public FilterRegistrationBean<CharacterEncodingFilter> characterEncodingFilterRegistration() {
  CharacterEncodingFilter filter = new CharacterEncodingFilter();
  filter.setEncoding("UTF-8"); // use your preferred encoding
  filter.setForceEncoding(true); // force the encoding

  FilterRegistrationBean<CharacterEncodingFilter> registrationBean =
    new FilterRegistrationBean<>(filter); // register the filter
  registrationBean.addUrlPatterns("/*"); // set preferred url
  return registrationBean;
}

reference