spring boot2.0 拦截器里面注入的dao为null

代码如下： 在拦截器里面注入一个CatalogService catalogService，调试发现是null

package top.bowen.interceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import top.bowen.pojo.Catalogs;
import top.bowen.service.CatalogService;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.HashMap;
@Component
public class GlobalParamsInterceptor implements HandlerInterceptor {
    @Autowired
    CatalogService catalogService;
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        /**
         * 全局添加分类信息
         */
        HashMap<Integer, Catalogs> catalogsHashMap = catalogService.catalogsHashMapList();
        request.setAttribute("catalogsHashMap",catalogsHashMap);
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    }
}

原因：

后面查资料发现
造成null的原因是因为拦截器加载是在springcontext创建之前完成的，所以在拦截器中注入实体自然就为null。
一般都是因为除了在拦截器之外，还需要在拦截器的配置类中，注册拦截器时没有使用spring的bean，而是使用了new创建bean造成的。

解决

解决方法就是让bean提前加载，将配置信息修改为如下：
不通过new 的方式创建GlobalParamsInterceptor而是自动注入，这样他就成了Spring的一个bean
关键代码：
@Autowired
private GlobalParamsInterceptor globalParamsInterceptor;

package top.bowen.config;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import top.bowen.interceptor.GlobalParamsInterceptor;
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Autowired
    private GlobalParamsInterceptor globalParamsInterceptor; **
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        /**
         * 拦截器按照顺序执行
         */
        /**
         * 不需要登录拦截的url
         */
        final String[] notLoginInterceptPaths = {"/static/**", "/error"};
        registry.addInterceptor(globalParamsInterceptor).addPathPatterns("/**")
                .excludePathPatterns(notLoginInterceptPaths);
    }
}