OAuth2ServiceRequestInterceptor.java

public class OAuth2ServiceRequestInterceptor implements RequestInterceptor {

    OAuth2AccessToken token;
    OAuth2RestTemplate serviceTemplate;

    public void setServiceTemplate(OAuth2RestTemplate serviceTemplate) {
        this.serviceTemplate = serviceTemplate;
    }

    @Override public void apply(RequestTemplate template) {
        injectAccessTokenInto(template);
    }

    void injectAccessTokenInto(RequestTemplate template) {
        String authHeaderValue = String.format("Bearer %s", accessToken());
        template.header(HttpHeaders.AUTHORIZATION, authHeaderValue);
    }

    OAuth2AccessToken accessToken() {
        if (token == null || token.isExpired()) {
            token = serviceTemplate.getAccessToken();
        }   
            
        return token;
    }

}