微信对接，获得openId

@RestController
@RequestMapping("/wx/login")
public class LoginController {

    //APPID 小程序唯一标识
    //SECRET 小程序的App secret
    private static final String APPID = "";
    private static final String SECRET = "";

    private static final String URL = "https://api.weixin.qq.com/sns/jscode2session?appid=APPID" +
            "&secret=SECRET&js_code=CODE&grant_type=authorization_code";

    @Autowired
    private UserService userService;

    @Value("${token.max.age}")
    private int tokenMaxAge;

    @Autowired
    private RedisTemplate redisTemplate;

    @GetMapping("/login")
    public Result login(String username) {
        User user = userService.findByUsername(username);
        if(null == user)
            return ResultUtil.genFail(ErrorCode.USER_NOT_EXIST, "用户不存在");

        //保存token
        String tokenId=UUIDUtil.getNewValue();
        CurrentUser currentUser = buildCurrentUser(user);
        redisTemplate.opsForValue().set(Constant.KEY_REDIS_TOKEN_PREFIX+tokenId, currentUser);

        return ResultUtil.genSuccess(null,tokenId);
    }


    @GetMapping("/power")
    public Result loginWx(@Valid Login login) {
        //获取openId
        String openId = getOpenId(login.getCode());

        //获取用户信息
        User user = userService.findByUsername(openId);
        if(null == user){
            user = new User();
            user.setUsername(openId);
            user.setLastLoginTime(System.currentTimeMillis()/1000);
            userService.add(user);
        } else {
            //更新用户登录信息
            userService.updateLastLoginTime(openId);
        }

        //保存token
        String tokenId=UUIDUtil.getNewValue();
        CurrentUser currentUser = buildCurrentUser(user);
        redisTemplate.opsForValue().set(Constant.KEY_REDIS_TOKEN_PREFIX+tokenId, currentUser);

        return ResultUtil.genSuccess(null,tokenId);
    }

    /**
     * 从微信获取用户openId
     * */
    private String getOpenId(String code) {
        try {
            String requestUrl = URL.replace("APPID", APPID).replace("SECRET", SECRET).replace("CODE", code);
            //获取返回的code

            HttpClient httpClient = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(requestUrl);
            ResponseHandler responseHandler = new BasicResponseHandler();
            //向微信发送请求并获取response
            String response = httpClient.execute(httpGet,responseHandler);
            JsonObject jsonObject = (JsonObject) new JsonParser().parse(response);
            return jsonObject.get("openid").getAsString();
        } catch (IOException e) {
            e.printStackTrace();
            throw new MyException("获取openId失败");
        }
    }

    /**
     * 构建当前用户信息
     * */
    private CurrentUser buildCurrentUser(User user) {
        CurrentUser currentUser = new CurrentUser();
        currentUser.setUserName(user.getUsername());
        return currentUser;
    }