Spring配置ArgumentResolver，统一进行session鉴定

一.编写WebMvcConfig配置类：

重写addArgumentResolvers方法，将解析类加入

@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

    @Autowired
    UserArgumentResolver userArgumentResolver;//这个解析类，第二步去编写

    @Override  //用来解析controller的参数类型的，xxx.class的参数可以被用来判断xxx
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(userArgumentResolver);
        super.addArgumentResolvers(argumentResolvers);
    }
}

二.编写ArgumentResolver解析类：

@Component
public class UserArgumentResolver implements HandlerMethodArgumentResolver {

    @Autowired
    MiaoshaUserService userService;//业务逻辑
    
　　@Overrid     //判断是否是支持的参数类型
    public boolean supportsParameter(MethodParameter parameter) {
        Class<?> clazz = parameter.getParameterType();
        return clazz==MiaoshaUser.class;  //也就是，如果是MiaoshaUser做参数的话，必须得走下面的解析方法
    }

　　@Overrid     //如果是支持的参数类型，调用此方法解析
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
        //从传入的参数获取不了内容，那么可以从request入手
        MiaoshaUser user = getUser(request,response);
        if(user==null){
            render(response,CodeMsg.SESSION_ERROR);
        }
        return user;//返回给controller
    }

    //向浏览器写出json
    private void render(HttpServletResponse response, CodeMsg cm)throws Exception {
        response.setContentType("application/json;charset=UTF-8");
        OutputStream out = response.getOutputStream();
        String str  = JSON.toJSONString(Result.error(cm));
        out.write(str.getBytes("UTF-8"));
        out.flush();
        out.close();
    }

    //从请求中获取用户信息    封装重复逻辑（统一session鉴定）
    private MiaoshaUser getUser(HttpServletRequest request, HttpServletResponse response) {
        //尝试从request里取
        String paramToken = request.getParameter(MiaoshaUserService.COOKI_NAME_TOKEN);
        //尝试从cookie里取，因为有时cookie禁用了，前端得从request传过来
        String cookieToken = getCookieValue(request, MiaoshaUserService.COOKI_NAME_TOKEN);
        if(StringUtils.isEmpty(cookieToken) && StringUtils.isEmpty(paramToken)) {
            return null;
        }
        String token = StringUtils.isEmpty(paramToken)?cookieToken:paramToken;
        return userService.getByToken(response, token);
    }

    private String getCookieValue(HttpServletRequest request, String cookiName) {
        Cookie[]  cookies = request.getCookies();
        if(cookies == null || cookies.length <= 0){
            return null;
        }
        for(Cookie cookie : cookies) {
            if(cookie.getName().equals(cookiName)) {
                return cookie.getValue();
            }
        }
        return null;
    }
}

三.修改Controller入口参数类型：

未使用argumentResolver:
@RequestMapping(value="/to_list")
    //@ResponseBody
    public String list(HttpServletRequest request, HttpServletResponse response, Model model) {

        String paramToken = request.getParameter(MiaoshaUserService.COOKI_NAME_TOKEN);
        //尝试从cookie里取，因为有时cookie禁用了，前端得从request传过来
        String cookieToken = getCookieValue(request, MiaoshaUserService.COOKI_NAME_TOKEN);
        if(StringUtils.isEmpty(cookieToken) && StringUtils.isEmpty(paramToken)) {
            return null;
        }
        String token = StringUtils.isEmpty(paramToken)?cookieToken:paramToken;
　　　　　//根据token查找从缓存查找user，获取

　　　　　MiaoshaUser user = xxxService.getUserByToken(token)；

　　　　　......　　

修改后：直接传入user：
 @RequestMapping(value="/to_list")
    //@ResponseBody
    public String list(HttpServletRequest request, HttpServletResponse response, Model model, MiaoshaUser user) {
        // 一般是token，然后对token从redis取user，user为空抛异常跳转（或者给出异常json），这里通过argumentResolver来封装成user；