> curl 'http://localhost:8080/user/1,2,3'
[
  {
    "user_id":1,
    "other_suff":...
  },
  {
    "user_id":2,
    "other_suff":...
  },
  {
    "user_id":3,
    "other_suff":...
  }
]

[
  {
    "user_info":{
      "user_id":1,
      "other_suff":...
    },
    "order_info":{
      "order_id":1,
      "user_id":1,
      "other_suff":...
    }
  },
  {
    "user_info":{
      "user_id":2,
      "other_suff":...
    },
    "order_info":{
      "order_id":2,
      "user_id":2,
      "other_suff":...
    }
  },
  {
    "user_info":{
      "user_id":3,
      "other_suff":...
    },
    "order_info":{
      "order_id":3,
      "user_id":3,
      "other_suff":...
    }
  }
]

type Content []map[string]interface{}

func (c Content) GetByFieldName(name string, defaultVal interface{}) infterface{} {
  for _, item := range c {
    val, ok := item[name]
    if !ok {
      continue
    }
    if val == nil {
      return defaultVal
    }
    return val
  }
  return defaultVal
}

func getUserContentByIDs(ids []int) Content {
  ...
  var c Content
  err := json.Unmarshal(jsonData, &c) 
  ...
  return c
}

func getOrderContentByUserIDs(ids []int) Content {.../*同上*/}

func Handler(userIDs []int) []Combine {

  users := getUserContentByIDs(userIDs)
  orders := getOrderContentByUserIDs(userIDs)

  // 这里假设用户和订单是一对一的关系
  ret := make([]Combine, 0, len(users))
  for _, u := range users {
    for _, o := range orders {
      userID := u.GetByFieldName("user_id", 0) 
      orderUserID := o.GetByFieldName("user_id", 0)
      if userID != 0 && userID == orderUserID {
        ret = append(ret, Combine{
          UserInfo: u,
          OrderInfo: o,
        })
        break
      }
    }
  }
  return ret
}