Initialize default Locale and Timezone with Spring configuration

I found Spring loads some of its default beans including other beans before calling the contextInitialized method, so, here is a better approach "draft" that I can think of, let me know if you see any concern:

public class SystemPropertyDefaultsInitializer 
    implements WebApplicationInitializer{

    private static final Logger logger = Logger
            .getLogger(SystemPropertyDefaultsInitializer.class);

    @Override
    public void onStartup(ServletContext servletContext)
            throws ServletException {
        logger.info("SystemPropertyWebApplicationInitializer onStartup called");

        // can be set runtime before Spring instantiates any beans
        // TimeZone.setDefault(TimeZone.getTimeZone("GMT+00:00"));
        TimeZone.setDefault(TimeZone.getTimeZone("UTC"));

        // cannot override encoding in Spring at runtime as some strings have already been read
        // however, we can assert and ensure right values are loaded here

        // verify system property is set
        Assert.isTrue("UTF-8".equals(System.getProperty("file.encoding")));

        // and actually verify it is being used
        Charset charset = Charset.defaultCharset();
        Assert.isTrue(charset.equals(Charset.forName("UTF-8")));

        // locale
        // set and verify language

    }

}

It may make sense to ensure that these are set before any beans are processed or initialized, as any beans created before this code is run could end up using the previous system default values. If you are using Spring Boot, you could do this in the main method before even initializing Spring:

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        Locale.setDefault(Locale.US);
        TimeZone.setDefault(TimeZone.getTimeZone("America/New_York"));

        SpringApplication.run(Application.class, args);
    }
}

If this needs to be run as part of a context that doesn't call the main method, e.g. in a JUnit integration test, you would need to make sure that it's called:

@SpringBootTest
public class ApplicationTest {
    @BeforeClass
    public static void initializeLocaleAndTimeZone() {
        // These could be moved into a separate static method in
        // Application.java, to be called in both locations
        Locale.setDefault(Locale.US);
        TimeZone.setDefault(TimeZone.getTimeZone("America/New_York"));
    }

    @Test
    public void applicationStartsUpSuccessfully() {
    }
}

I've used a ServletContextListener. In contextInitialized(..) TimeZone.setDefault(..) is called.

It won't be taken into account if you rely on the timezone in any constructor or @PostConstruct / afterPropertiesSet() though.

If you need it, take a look at this question