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场景：用户扫描微信公众号的二维码，关注后自动登录网站，若已关注则直接登录。
逻辑： 1.系统生成带参数（此参数自定义为唯一值）的临时二维码（微信公众平台有提供该接口，可查看一下开发文档）； 2.用户使用微信扫描该二维码，关注后微信服务器会将数据（自定义参数、openid…）返回到我们的服务器； 3.我们服务器将接收到的openid再次向微信服务器发起请求，获取该用户的信息（昵称、头像、地域、unionid(若绑定了微信开放平台，则有此参数)）； 4.我们将返回的用户信息存储到数据库，用作于登录。
准备工作：登录微信公众平台，在基本配置下，查看appid和设置appsecret、回调URL、token，小编这里使用的是测试账号，因为正式的要审核（收费300个大洋），如下图：   小编是使用springMVC+mybatis开发的，为了方便展示，小编将代码都写在同一个controller下了，你们自己可以做下拆分，代码如下：
package com.lrfun.web.controller;
import java.io.InputStream;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclienthods.ByteArrayRequestEntity;
import org.apache.commons.httpclienthods.GetMethod;
import org.apache.commons.httpclienthods.PostMethod;
import org.apache.commons.httpclienthods.RequestEntity;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.ModelAndView;
import com.google.gson.Gson;
@Controller
public class WechatController {
//Lrfun测试公众号
private static final String app_id = "xxx";
private static final String app_secret = "xxx";
private static final Gson gson = new Gson();
/***
* httpClient-Get请求
* @param url 请求地址
* @return
* @throws Exception
*/
public static Map httpClientGet(String url) throws Exception {
HttpClient client = new HttpClient();
client.getParams().setContentCharset("UTF-8");
GetMethod httpGet = new GetMethod(url);
try {
client.executeMethod(httpGet);
String response = httpGet.getResponseBodyAsString();
Map map = gson.fromJson(response, Map.class);
return map;
} catch (Exception e) {
throw e;
} finally {
httpGet.releaseConnection();
}
}
/***
* httpClient-Post请求
* @param url 请求地址
* @param params post参数
* @return
* @throws Exception
*/
public static Map httpClientPost(String url, String params) throws Exception {
HttpClient client = new HttpClient();
client.getParams().setContentCharset("UTF-8");
PostMethod httpPost = new PostMethod(url);
try {
RequestEntity requestEntity = new ByteArrayRequestEntity(params.getBytes("utf-8"));
httpPost.setRequestEntity(requestEntity);
client.executeMethod(httpPost);
String response = httpPost.getResponseBodyAsString();
Map map = gson.fromJson(response, Map.class);
return map;
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
httpPost.releaseConnection();
}
}
// 获取access_tocken
private String getAccessToken() throws Exception{
String url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + app_id + "&secret=" + app_secret;
Map accessTokenMap = WechatController.httpClientGet(url);
System.out.println(accessTokenMap);
return accessTokenMap.get("access_token").toString();
}
// 通过openid获取用户信息
private Map getUserInfoByOpenid(String openid) throws Exception {
String access_tocken = getAccessToken();
String url = "https://api.weixin.qq.com/cgi-bin/user/info?access_token=" + access_tocken + "&openid=" + openid;
Map map = httpClientGet(url);
return map;
}
// 生成带参数的二维码，扫描关注微信公众号，自动登录网站
@RequestMapping(value = "/wechat/mpLogin.html")
public ModelAndView wechatMpLogin(ModelMap modelMap) throws Exception {
String access_token = getAccessToken();
String url = "https://api.weixin.qq.com/cgi-bin/qrcode/create?access_token=" + access_token;
String scene_str = "lrfun.com." + new Date().getTime();
String params = "{\"expire_seconds\":600, \"action_name\":\"QR_STR_SCENE\", \"action_info\":{\"scene\":{\"scene_str\":\"" + scene_str + "\"}}}";
Map resultMap = httpClientPost(url, params);
if (resultMap.get("ticket") != null) {
String qrcodeUrl = "https://mp.weixin.qq.com/cgi-bin/showqrcode?ticket=" + resultMap.get("ticket");
modelMap.put("qrcodeUrl", qrcodeUrl);
}
modelMap.put("scene_str", scene_str);
return new ModelAndView("/test/wechatMpLogin.vm", modelMap);
}
// 检测登录
@RequestMapping("/wechat/checkLogin.html")
public @ResponseBody Map wechatMpCheckLogin(String scene_str){
// 根据scene_str查询数据库，获取对应记录
// SELECT * FROM wechat_user_info WHERE event_key='scene_str';
Map returnMap = new HashMap();
if (true) {
returnMap.put("result", "true");
} else {
returnMap.put("result", "false");
}
return returnMap;
}
// 回调函数
@RequestMapping(value = "/wechat/callback.html")
public void callback(HttpServletRequest httpServletRequest) throws Exception {
Map callbackMap = xmlToMap(httpServletRequest); //获取回调信息
//下面是返回的xml
// //微信公众号的微信号
// //openid用于获取用户信息，做登录使用
//1531130986 //回调时间
//
//
// //上面自定义的参数（scene_str）
// //换取二维码的ticket
//
if (callbackMap != null && callbackMap.get("FromUserName").toString() != null) {
// 通过openid获取用户信息
Map wechatUserInfoMap = getUserInfoByOpenid(callbackMap.get("FromUserName"));
// 将数据写入到数据库中，前面自定义的参数（scene_str）也需记录到数据库中，后面用于检测匹配登录
// INSERT INTO wechat_user_info......(数据库操作)
}
}
// xml转为map
private Map xmlToMap(HttpServletRequest httpServletRequest) {
Map map = new HashMap();
try {
InputStream inputStream = httpServletRequest.getInputStream();
SAXReader reader = new SAXReader(); // 读取输入流
org.dom4j.Document document = reader.read(inputStream);
Element root = document.getRootElement(); // 得到xml根元素
List elementList = root.elements(); // 得到根元素的所有子节点
// 遍历所有子节点
for (Element e : elementList)
map.put(e.getName(), e.getText());
// 释放资源
inputStream.close();
inputStream = null;
return map;
} catch (Exception e) {
e.getMessage();
}
return null;
}
}
静态文件wechatMpLogin.vm：
微信扫码，关注登录
a{outline:0}h1,h2,h3,h4,h5,h6,p{margin:0;font-weight:400}a img,fieldset{border:0}body{font-family:"Microsoft Yahei";color:#fff;background:0 0}.impowerBox{display:inline-block;vertical-align:middle;line-height:1.6;position:relative;width:100%;z-index:1;text-align:center}.impowerBox .title{text-align:center;font-size:20px}.impowerBox .qrcode{width:280px;height:280px;margin-top:15px;border:1px solid #E2E2E2}.impowerBox .info{width:280px;margin:0 auto}.impowerBox .status{padding:7px 14px;text-align:left}.impowerBox .status.normal{margin-top:15px;background-color:#232323;border-radius:100px;-moz-border-radius:100px;-webkit-border-radius:100px;box-shadow:inset 0 5px 10px -5px #191919,0 1px 0 0 #444;-moz-box-shadow:inset 0 5px 10px -5px #191919,0 1px 0 0 #444;-webkit-box-shadow:inset 0 5px 10px -5px #191919,0 1px 0 0 #444}.impowerBox .status.status_browser{text-align:center}.impowerBox .status p{font-size:13px}
微信登录
请使用微信扫描二维码登录
“lrfun.com”
$(document).ready(function () {
setInterval("wechatCheckLogin()", 2000);
});
function wechatCheckLogin(){
$.post("/wechat/checkLogin.html", {scene_str:"$!{scene_str}"}, function(data){
if(data.result == "true"){
alert("成功，登录跳转！");
} else {
alert("失败！");
}
}, "JSON");
}
看了下评论，可能小编有些地方写得不是很清楚，画了一幅图解释一下整个流程（可能画得跟表达得不是很好，大家多多见谅） 
更多文章可查看小编的个人博客网站：www.lrfun.com
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