第一步：在小程序中点击授权按钮，并发送授权码给后端服务接口

 @PostMapping("login")
    @ApiOperation("微信登陆")
    public Result<UserLoginVO> login(@RequestBody UserLoginDTO userLoginDTO)
    {
        log.info("微信用户登陆：{}",userLoginDTO.getCode());
        User user=userService.wxLogin(userLoginDTO);
        HashMap<String, Object> map = new HashMap<>();
        map.put(JwtClaimsConstant.USER_ID,user.getId());
        String token=JwtUtil.createJWT(jwtProperties.getUserSecretKey(),jwtProperties.getUserTtl(),map);
       UserLoginVO userLoginVO = UserLoginVO.builder()
                .id(user.getId())
                .openid(user.getOpenid())
                .token(token)
                .build();
        return  Result.success(userLoginVO);
    }

第二步：后端接口得到授权码和自己的小程序id和密钥等信息 向微信服务接口发起请求得到openid

public User wxLogin(UserLoginDTO userLoginDTO) {
   String openid=getOpenId(userLoginDTO.getCode());
    if(openid == null)
        throw new LoginFailedException(MessageConstant.LOGIN_FAILED);
    User user=userMapper.getByUserId(openid);
    if (user == null) {
            user=User
                .builder()
                .openid(openid)
                .createTime(LocalDateTime.now())
                .build();
            userMapper.insert(user);
    }
    return user;
}
private  String getOpenId(String code)
{
    // 调用微信服务 获取openid
    HashMap<String,String> map = new HashMap<>();
    map.put("appid", wechatProperties.getAppid());
    map.put("secret",wechatProperties.getSecret());
    map.put("js_code", code);
    map.put("grant_type","authorization_code");
    log.info("appid:{}     js_code:{}",wechatProperties.getAppid(),code);
    String json= HttpClientUtil.doGet(WX_LOGIN,map);
    JSONObject jsonObject = JSON.parseObject(json);
    String openid = jsonObject.getString("openid");
    return openid;
}

第三步：

处理数据 将openid放入user(有则加入openid 无则注册) 返回后使用jwt处理结果得到token返回结果