Spring MVC 4 with Spring boot and thymeleaf - i18n not working

I'm trying to make a simple internationalization example in spring mvc 4 with spring boot, but it's not working. Here is my web app structure

And here's my java configuration:

import java.util.Locale;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor;
import org.springframework.web.servlet.i18n.SessionLocaleResolver;

@Configuration
public class WebConfiguration extends WebMvcConfigurerAdapter
{
    @Bean
    public LocaleResolver localeResolver() {
        SessionLocaleResolver localeResolver = new SessionLocaleResolver();
        Locale defaultLocale = new Locale("en_US");
        localeResolver.setDefaultLocale(defaultLocale);
        return localeResolver;
    }

    @Bean
    public LocaleChangeInterceptor localeChangeInterceptor() {
        LocaleChangeInterceptor localeChangeInterceptor = new
                LocaleChangeInterceptor();
        localeChangeInterceptor.setParamName("lang");
        return localeChangeInterceptor;
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(localeChangeInterceptor());
    }
}

My Thymeleaf page:

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <meta name="viewport"
        content="width=device-width, initialscale=1, maximum-scale=1.0, user-scalable=no" />
    <title>Home</title>

    <!-- CSS Links -->
</head>
<body>
    <div class="container">
        <div class="row">
            <p th:text="#{welcome}">Hello</p>
        </div>
    </div>
</body>
</html>

and I defined welcome message in both messages properties files, and I put the following in the application.properties file:

spring.messages.basename=messages
spring.messages.encoding=UTF-8

when I hit localhost:8080/home, it prints out ??welcome_en_us??. I don't know what i have missed. And I found some people writing the basename as "classpath:messages', what does that mean? I mean isn't my project structure right and should put the properties files elsewhere?