springboot拦截器自动注入为null解决办法和具体原因分析

前言

最近在使用springboot拦截器的过程当中，发现无法注入service,提示NPE错误

内容

问题复现

springboot拦截器注册方式：

@Configuration
public class MyWebMvcConfigurer implements WebMvcConfigurer {
	
  @Override
  public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(new SessionInterceptor()).excludePathPatterns("/static/**").addPathPatterns("/**");
  }
}

拦截器代码：

public class SessionInterceptor  implements HandlerInterceptor {
    @Autowired
    private IUserService  userService;

    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        HttpSession session = httpServletRequest.getSession();
        String username = (String)session.getAttribute("userName");
        //获取请求信息的用户名获取对应的用户信息
        SysUser userInfo =userService.getUserInfoByUserName(username).get(0);
    }

项目运行，发起请求，进入拦截器，直接报错NPE，userService为null。

解决方式:

方式一：使用WebApplicationContext上下文对象来手动注入
方式二：通过@bean注解注入拦截器到spring当中,同时给拦截器加上@compent注解

@Configuration
public class MyWebMvcConfigurer implements WebMvcConfigurer {
  @Bean
  public SessionInterceptor getSessionInterceptor(){
    return new SessionInterceptor();
  }

  @Override
  public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(getSessionInterceptor()).excludePathPatterns("/static/**").addPathPatterns("/**");
  }
}