That's because Spring isn't managing your PagePopulationInterceptor instance. You are creating it yourself in the below （拦截器内使用@Autowired时出现了null，这是由于你的spring对象注入时机在你的拦截器之后了）

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

change that to

@Bean
public PagePopulationInterceptor pagePopulationInterceptor() {
    return new PagePopulationInterceptor();
}

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

in this way, Spring will manage the lifecycle of the PagePopulationInterceptor instance since it's generated from a @Bean method. Spring will scan it for @Autowired targets and inject them.
This assumes that PagePopulationInterceptor is in a package to be @ComponentScaned.