在项目中遇到一个问题，在 Filter中注入 Serivce失败，注入的service始终为null。如下所示：
public class WeiXinFilter implements Filter{ @Autowired private UsersService usersService;
在 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 方法中使用 usersService 时报空指针异常。
解决方法：
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest req = (HttpServletRequest)request; HttpServletResponse resp = (HttpServletResponse)response; XmlWebApplicationContext context = (XmlWebApplicationContext)WebApplicationContextUtils.
getWebApplicationContext(req.getSession().getServletContext()); if(context != null && context.getBean("usersService") != null && usersService == null) usersService = (UsersService) context.getBean("usersService"); Users users = this.usersService.queryByOpenid(openid);
这样就行了。