// 登錄
  wx.login({
   success: res => {
    // 發送 res.code 到后臺換取 openId, sessionKey, unionId
    if (res.code) {
     wx.request({
      url: 'http://localhost:84/user/login',
      method: 'POST',
      data: {
       code: res.code
      },
      header: {
       'content-type': 'application/x-www-form-urlencoded'
      },
      success(res) {
       console.log("openid:"+res.data.openid);
       if (res.data.openid != "" || res.data.openid!=null){
        // 登錄成功
        wx.setStorageSync("openid", res.data.openid);//將用戶id保存到緩存中
        wx.setStorageSync("session_key", res.data.session_key);//將session_key保存到緩存中
       }else{
        // 登錄失敗
        // TODO 跳轉到錯誤頁面，要求用戶重試


        return false;
       }
      }
     })
    } else {
     console.log('獲取用戶登錄態失敗！' + res.errMsg)
    }
   }
  })

package com.ft.feathertrade.handler;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.ft.feathertrade.entity.OpenIdJson;
import com.ft.feathertrade.utils.HttpUtil;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.io.IOException;

@RestController
public class LoginHandler {

  private String appID = "";
  private String appSecret = "";

  @PostMapping("/user/login")
  public String userLogin(@RequestParam("code") String code) throws IOException {
    String result = "";
    try{//請求微信服務器，用code換取openid。HttpUtil是工具類，后面會給出實現，Configure類是小程序配置信息，后面會給出代碼
      result = HttpUtil.doGet(
          "https://api.weixin.qq.com/sns/jscode2session?appid="
              + this.appID + "&secret="
              + this.appSecret + "&js_code="
              + code
              + "&grant_type=authorization_code", null);
    }
    catch (Exception e) {
      e.printStackTrace();
    }
    ObjectMapper mapper = new ObjectMapper();
    OpenIdJson openIdJson = mapper.readValue(result,OpenIdJson.class);
    System.out.println(result.toString());
    System.out.println(openIdJson.getOpenid());
    return result;
  }

}

package com.ft.feathertrade.utils;


import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Set;
import org.apache.commons.httpclient.HttpStatus;//此類需要添加maven依賴或jar包

/** 將此依賴添加到pom.xml中
 <dependency>
 <groupId>commons-httpclient</groupId>
 <artifactId>commons-httpclient</artifactId>
 <version>3.1</version>
 </dependency>
 **/

public class HttpUtil {

  public static String doGet(String urlPath, HashMap<String, Object> params)
      throws Exception {
    StringBuilder sb = new StringBuilder(urlPath);
    if (params != null && !params.isEmpty()) { // 說明有參數
      sb.append("?");

      Set<Entry<String, Object>> set = params.entrySet();
      for (Entry<String, Object> entry : set) { // 遍歷map里面的參數
        String key = entry.getKey();
        String value = "";
        if (null != entry.getValue()) {
          value = entry.getValue().toString();
          // 轉碼
          value = URLEncoder.encode(value, "UTF-8");
        }
        sb.append(key).append("=").append(value).append("&");
      }

      sb.deleteCharAt(sb.length() - 1); // 刪除最后一個&
    }
    // System.out.println(sb.toString());
    URL url = new URL(sb.toString());
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setConnectTimeout(5000); // 5s超時
    conn.setRequestMethod("GET");

    if (conn.getResponseCode() == HttpStatus.SC_OK) {// HttpStatus.SC_OK ==
      // 200
      BufferedReader reader = new BufferedReader(new InputStreamReader(
          conn.getInputStream()));
      StringBuilder sbs = new StringBuilder();
      String line;
      while ((line = reader.readLine()) != null) {
        sbs.append(line);
      }
      return sbs.toString();
    }
    return null;
  }
}

package com.ft.feathertrade.entity;

public class OpenIdJson {
  private String openid;
  private String session_key;

  public String getOpenid() {
    return openid;
  }

  public void setOpenid(String openid) {
    this.openid = openid;
  }

  public String getSession_key() {
    return session_key;
  }

  public void setSession_key(String session_key) {
    this.session_key = session_key;
  }
}