public ResultCode resultCode; // 業(yè)務(wù)響應(yīng)碼
 public String resultMsg = ""; // 返回信息描述
 public String errCode; // 錯(cuò)誤代碼
 public String errCodeDes = ""; // 錯(cuò)誤描述
 public Object data; // 返回業(yè)務(wù)數(shù)據(jù)
  public enum ResultCode {
  SUCCESS, // 業(yè)務(wù)處理成功
  FAIL; // 業(yè)務(wù)處理失敗
 }

App({
   globalData: {
    serverHost: 'http://localhost:8080', //服務(wù)器域名
   },
   onLaunch: function() {
    var that = this;
    //檢查登錄態(tài)是否過期
    wx.checkSession({
     success() {
      // session_key 未過期，并且在本生命周期一直有效
      console.log("【用戶小程序登錄態(tài)未過期】");
      that.isRegister();
     },
     fail() {
      // session_key 已經(jīng)失效，需要重新執(zhí)行登錄流程
      that.wxLogin();
     }
    })
   },
   //查看當(dāng)前用戶是否已經(jīng)注冊(cè)過
   isRegister: function() {
    var that = this;
    var host = this.globalData.serverHost;
    // （先從緩存查該用戶，有就是老用戶，沒有就后臺(tái)查有沒有這個(gè)用戶，后臺(tái)查到有這個(gè)用戶就放緩存，沒有就是新用戶）
    wx.getStorage({
     key: 'registered',
     success(res) {
      console.log("【通過緩存查詢到該用戶是已經(jīng)注冊(cè)過的】");
      console.log("【當(dāng)前用戶的openid為:】" + wx.getStorageSync('openid'));
     },
     fail(res) {
      var openid;
      openid = wx.getStorageSync('openid');
      wx.request({
       url: host + '寫自己的后臺(tái)請(qǐng)求檢查用戶存不存在的URL',
       method: 'POST',
       data: {
        openId: openid,
       },
       header: {
        "Content-Type": "application/x-www-form-urlencoded"
       },
       success: (res) => {
        if (后臺(tái)返回注冊(cè)過") {
         if (res.data.data) {
          console.log("【通過后臺(tái)查詢到該用戶已經(jīng)注冊(cè)過】");
          wx.setStorage({
           key: "registered",
           data: true
          });
         } else {
          console.log("【通過后臺(tái)查詢到該用戶還沒注冊(cè)過】");
         }
        }
       }
      })
     },
    })
   },
   //該函數(shù)用來登錄的
   wxLogin: function() {
    var that = this;
    //設(shè)置后臺(tái)host
    var host = this.globalData.serverHost;
    console.log("【用戶重新執(zhí)行小程序登錄流程】");
    wx.login({
     success(res) {
      // 發(fā)起網(wǎng)絡(luò)請(qǐng)求,發(fā)送 res.code 到后臺(tái)換取 openId
      if (res.code) {
       var code = res.code;
       wx.request({
        url: host + '寫自己后臺(tái)用code換取OpenId的請(qǐng)求URL',
        method: 'POST',
        data: {
         code: code,
        },
        header: {
         "Content-Type": "application/x-www-form-urlencoded"
        },
        success: (res) => {
         console.log("【獲取用戶openid成功】");
         console.log("【從后臺(tái)獲取到用戶openid為】" + res.data.data.openid)
         let openId = res.data.data.openid;
         wx.setStorage({
          key: "openid",
          data: res.data.data.openid
         });
         console.log("【用戶openid放入緩存成功】");
         that.isRegister();
        }
       })
      }
     }
    })
   },
 },
})

import net.sf.json.JSONObject;
/**
 * @author niqinhua
 * @date 2019/3/8 9:19
 */
public class WXUtil {
  public static JSONObject getOpenidAndSessionKey(String code) {
    String url = "https://api.weixin.qq.com/sns/jscode2session";
    String param = "appid=寫自己的appId&secret=寫自己的密鑰&js_code=" +
         code + "&grant_type=authorization_code";
    String wxReturnResult = sendGet(url, param);
    JSONObject wxReturnResultObject = JSONObject.fromObject(wxReturnResult);
    return wxReturnResultObject;
  }
 /**
   * 從規(guī)范上，建議把這個(gè)方法抽出來放到HttpUtil類里面
   * 向指定URL發(fā)送GET方法的請(qǐng)求
   * @param url 發(fā)送請(qǐng)求的URL
   * @param param 請(qǐng)求參數(shù)，請(qǐng)求參數(shù)應(yīng)該是 name1=value1&name2=value2 的形式。
   * @return URL 所代表遠(yuǎn)程資源的響應(yīng)結(jié)果
   */
  public static String sendGet(String url, String param) {
    String result = "";
    BufferedReader in = null;
    try {
      String urlNameString = url + "?" + param;
      URL realUrl = new URL(urlNameString);
      // 打開和URL之間的連接
      URLConnection connection = realUrl.openConnection();
      // 設(shè)置通用的請(qǐng)求屬性
      connection.setRequestProperty("accept", "*/*");
      connection.setRequestProperty("connection", "Keep-Alive");
      connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
      // 建立實(shí)際的連接
      connection.connect();
      // 定義 BufferedReader輸入流來讀取URL的響應(yīng)
      in = new BufferedReader(new InputStreamReader(
          connection.getInputStream()));
      String line;
      while ((line = in.readLine()) != null) {
        result += line;
      }
    } catch (Exception e) {
      System.out.println("【HTTP發(fā)送GET請(qǐng)求出現(xiàn)異?！?訪問URL："+url+",錯(cuò)誤："+e.getMessage());
    }
    // 使用finally塊來關(guān)閉輸入流
    finally {
      try {
        if (in != null) {
          in.close();
        }
      } catch (Exception e2) {
        System.out.println("【HTTP請(qǐng)求關(guān)閉輸入流異?！?訪問URL："+url+",錯(cuò)誤："+e2.getMessage());
      }
    }
    return result;
  }
}

JSONObject wxReturnJson = WXUtil.getOpenidAndSessionKey(code);
if (wxReturnJson.get("errCode")!=null) {
  //log.error("【獲取用戶的openid】【失敗】【傳遞參數(shù)code無效】");
} else {
  //log.info("【獲取用戶的openid】【成功】【傳遞參數(shù)code無效】");
}