高并发秒杀系统方案（分布式session）

编程要有一个习惯：做参数校验

所谓的分布式session：就是用redis统一管理session。

我们这里的思路是：把token写入cookie中，客户端在随后的访问中携带cookie，服务端就能根据cookie中携带的token去redis中查找到user信息。

这里要注意：session的有效期是用户最后的访问时间加session的过期时间

关键代码：

        //生成cookie

        String token     = UUIDUtil.uuid();

        addCookie(response, token, user);

        return true;

    }

    private void addCookie(HttpServletResponse response, String token, MiaoshaUser user) {

        redisService.set(MiaoshaUserKey.token, token, user);

        Cookie cookie = new Cookie(COOKI_NAME_TOKEN, token);

        cookie.setMaxAge(MiaoshaUserKey.token.expireSeconds());

        cookie.setPath("/");

        response.addCookie(cookie);

    }

UserArgumentResolver：

package com.imooc.miaosha.config;

import javax.servlet.http.Cookie;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang3.StringUtils;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.core.MethodParameter;

import org.springframework.stereotype.Service;

import org.springframework.web.bind.support.WebDataBinderFactory;

import org.springframework.web.context.request.NativeWebRequest;

import org.springframework.web.method.support.HandlerMethodArgumentResolver;

import org.springframework.web.method.support.ModelAndViewContainer;

import com.imooc.miaosha.domain.MiaoshaUser;

import com.imooc.miaosha.service.MiaoshaUserService;

@Service

public class UserArgumentResolver implements HandlerMethodArgumentResolver {

    @Autowired

    MiaoshaUserService userService;

    public boolean supportsParameter(MethodParameter parameter) {

        Class<?> clazz = parameter.getParameterType();

        return clazz==MiaoshaUser.class;

    }

    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);

        String paramToken = request.getParameter(MiaoshaUserService.COOKI_NAME_TOKEN);

        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();

        for(Cookie cookie : cookies) {

            if(cookie.getName().equals(cookiName)) {

                return cookie.getValue();

            }

        }

        return null;

    }

}

WebConfig：

package com.imooc.miaosha.config;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.context.annotation.Configuration;

import org.springframework.web.method.support.HandlerMethodArgumentResolver;

import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration

public class WebConfig  extends WebMvcConfigurerAdapter{

    @Autowired

    UserArgumentResolver userArgumentResolver;

    @Override

    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {

        argumentResolvers.add(userArgumentResolver);

    }

}

经过这样的配置以后，就可以直接获取user而不用通过token再获取user了：