开发微信小程序时，经常用到获取用户的openid，那么如何获取用户openid呢？

1.首先需要在小程序中获取用户的code。

如何获取code？
只需小程序用户登录就行。

   //登录
       wx.login({
           success: function (res) {
               //res.code 
               然后就请求你的后台接口获取。
           }, 
           fail: function () {

           }
       })

2、通过用户登录获取的code，请求微信接口获取openid。

注:一个code只能用一次，虽然微信小程序可以请求微信接口获取用户openid，但是发布版不行，需要添加安全域名，但是微信的域名不能存放在安全域名中，所有少年！放弃吧，用后台接口吧。

微信api接口："https://api.weixin.qq.com/sns/jscode2session"

请求参数说明：

我用的是java获取用户openid

    private Map _getOpenId(String code){
        Map ret = new HashMap();
      // 组装参数*****
        Map urlData= new HashMap();
        urlData.put("appid",appid);//小程序id
        urlData.put("secret",appKey);//小程序key
        urlData.put("grant_type","authorization_code");//固定值这样写就行
        urlData.put("js_code",code);//小程序传过来的code
        HttpsClientUtil httpsClientUtil = new HttpsClientUtil();
        Object data_deserialize = null;
        try {
            //code2OpenidUrl "https://api.weixin.qq.com/sns/jscode2session";
            String dataStr = httpsClientUtil.doGet(code2OpenidUrl, urlData);
            data_deserialize = JSONUtil.deserialize(dataStr);
        }catch(Exception ex){
            ret.put("success", false);
            ret.put("msg", "_getOpenId_未知异常");
            ret.put("message", ex);
            return ret;
        }
        Map data=  (Map)data_deserialize;
        if( data.containsKey("errcode") ){
            ret.put("success", false);
            ret.put("msg", data.containsKey("errcode"));
            ret.put("message", data.containsKey("errmsg"));
        }else{
            ret.put("success", true);
            ret.put("result",data);
        }
        return ret;
    }

我用的java请求微信的方法， 三种，get、post、postXml，每个人写的不同，每个库也不同，仅供参考。

public String doPost(String url, Map map) throws Exception{
        String result = null;
        HttpClient httpClient = new SSLClient();
        HttpPost httpPost = new HttpPost(url);
        //设置参数
        List list = new ArrayList();
        Iterator iterator = map.entrySet().iterator();
        wShopfale(iterator.hasNext()){
            Entry elem = (Entry) iterator.next();
            list.add(new BasicNameValuePair(elem.getKey(),elem.getValue()));
        }
        if(list.size() > 0){
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(list, "UTF-8");
            httpPost.setEntity(entity);
        }
        HttpResponse response = httpClient.execute(httpPost);
        if(response != null){
            HttpEntity resEntity = response.getEntity();
            if(resEntity != null){
                result = EntityUtils.toString(resEntity, "UTF-8");
            }
        }
        return result;
    }
    public String doGet(String url, Map map) throws Exception{
        String result = null;
        HttpClient httpClient = new SSLClient();
        String param="";
        for(String nameKey:map.keySet()){
            param += nameKey+"="+map.get(nameKey)+"&";
        }
        param = param.substring(0,param.length()-1);
        String urlNameString = url + "" + param;
        HttpGet httpGet = new HttpGet(urlNameString);
        HttpResponse response = httpClient.execute(httpGet);
        if(response != null){
            HttpEntity resEntity = response.getEntity();
            if(resEntity != null){
                result = EntityUtils.toString(resEntity, "UTF-8");
            }
        }
        return result;
    }
    public String doPostXml(String url, String xml) throws Exception{
        String result = null;
        HttpClient httpClient = new SSLClient();
        HttpPost httpPost = new HttpPost(url);
        httpPost.addHeader("Content-Type","text/xml;charset=UTF-8");
        StringEntity stringEntity = new StringEntity(xml, "UTF-8");
        stringEntity.setContentEncoding("UTF-8");

        httpPost.setEntity(stringEntity);
        HttpResponse response = httpClient.execute(httpPost);
        if(response != null){
            HttpEntity resEntity = response.getEntity();
            if(resEntity != null){
                result = EntityUtils.toString(resEntity, "UTF-8");
            }
        }
        return result;
    }