在Go中解析JSON

Question

我是Go的新手，我正在構建一個使用Android應用程序中RDW數據的Web API。 但是我在Go中解析JSON時遇到問題，就像在Java中一樣，我可以輕松地使用像jsonObject.getString("AreaId")這樣的東西。 我似乎不能在Go中做到這一點。

我試圖解析以下JSON以將其保存在MySQL數據庫中：

{
  'd': {
    'results': [
      {
        '__metadata': {
          'id': 'https://api.datamarket.azure.com/Data.ashx/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY(1)',
          'uri': 'https://api.datamarket.azure.com/Data.ashx/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY(1)',
          'type': 'opendata.rdw.StatischParkeren.Open.Data.AREAGEOMETRY'
        },
        'AREAGEOMETRY_ID': 1,
        'AreaManagerId': '34',
        'AreaId': 'ALMBUITEN',
        'EndDateArea': null,
        'StartDateArea': '/Date(1330560000000)/',
        'AreaGeometryTxt': 'POLYGON ((5.2736760005354881 52.391216600313783, 5.2752534225583076 52.392331821843982, 5.2771425843238831 52.391448376700282, 5.2795117920336709 52.392518069183787, 5.2794937640428543 52.392529543489218, 5.2795250192284584 52.392524041235447, 5.2795117920336709 52.392518069183787, 5.27959094196558 52.392467692494392, 5.28429589420557 52.394528595730662, 5.2830820381641388 52.3958012573421, 5.2826158106327057 52.396464187651873, 5.28216527402401 52.396755328401923, 5.2811877280473709 52.396325327456, 5.27938649058342 52.395481485873461, 5.2793451324105263 52.395514352247119, 5.2788525596261024 52.395813956856728, 5.278492659330368 52.39611235447228, 5.2776647135615349 52.396820867434144, 5.2777034044265747 52.396853528916836, 5.2768759876489639 52.397581102326512, 5.274177111685276 52.396415254101157, 5.2741994857788086 52.396424867212772, 5.2686141580343246 52.394008679315448, 5.26860549300909 52.394005045294762, 5.2691666409373283 52.39350445382297, 5.2705547362565994 52.392721636220813, 5.2723518460904533 52.392156438032842, 5.2723518460989 52.39215643890202, 5.272359311580658 52.392154090106487, 5.2723518460904533 52.392156438032842, 5.2723498195409775 52.391947904601693, 5.273051455616951 52.391403153538704, 5.2736760005354881 52.391216600313783))',
        'AreaGeometryGml': '<Polygon xmlns="http://www.opengis.net/gml"><exterior><LinearRing><posList>5.2736760005354881 52.391216600313783 5.2752534225583076 52.392331821843982 5.2771425843238831 52.391448376700282 5.2795117920336709 52.392518069183787 5.2794937640428543 52.392529543489218 5.2795250192284584 52.392524041235447 5.2795117920336709 52.392518069183787 5.27959094196558 52.392467692494392 5.28429589420557 52.394528595730662 5.2830820381641388 52.3958012573421 5.2826158106327057 52.396464187651873 5.28216527402401 52.396755328401923 5.2811877280473709 52.396325327456 5.27938649058342 52.395481485873461 5.2793451324105263 52.395514352247119 5.2788525596261024 52.395813956856728 5.278492659330368 52.39611235447228 5.2776647135615349 52.396820867434144 5.2777034044265747 52.396853528916836 5.2768759876489639 52.397581102326512 5.274177111685276 52.396415254101157 5.2741994857788086 52.396424867212772 5.2686141580343246 52.394008679315448 5.26860549300909 52.394005045294762 5.2691666409373283 52.39350445382297 5.2705547362565994 52.392721636220813 5.2723518460904533 52.392156438032842 5.2723518460989 52.39215643890202 5.272359311580658 52.392154090106487 5.2723518460904533 52.392156438032842 5.2723498195409775 52.391947904601693 5.273051455616951 52.391403153538704 5.2736760005354881 52.391216600313783</posList></LinearRing></exterior></Polygon>'
      },
      {
        '__metadata': {
          'id': 'https://api.datamarket.azure.com/Data.ashx/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY(2)',
          'uri': 'https://api.datamarket.azure.com/Data.ashx/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY(2)',
          'type': 'opendata.rdw.StatischParkeren.Open.Data.AREAGEOMETRY'
        },
        'AREAGEOMETRY_ID': 2,
        'AreaManagerId': '34',
        'AreaId': 'ALMTEGELZ',
        'EndDateArea': null,
        'StartDateArea': '/Date(1330560000000)/',
        'AreaGeometryTxt': 'POLYGON ((5.216308925 52.370733155, 5.216800447 52.370804276, 5.216837124 52.370755791, 5.217178542 52.370807152, 5.217373999 52.370322534, 5.217353484 52.370319431, 5.217371539 52.370274734, 5.216664547 52.370167441, 5.216571837 52.370396589, 5.216451509 52.370380301, 5.216308925 52.370733155))',
        'AreaGeometryGml': '<Polygon xmlns="http://www.opengis.net/gml"><exterior><LinearRing><posList>5.216308925 52.370733155 5.216800447 52.370804276 5.216837124 52.370755791 5.217178542 52.370807152 5.217373999 52.370322534 5.217353484 52.370319431 5.217371539 52.370274734 5.216664547 52.370167441 5.216571837 52.370396589 5.216451509 52.370380301 5.216308925 52.370733155</posList></LinearRing></exterior></Polygon>'
      },
 ],
    '__next': 'https://api.datamarket.azure.com/Data.ashx/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY?$skiptoken=100'
  }
}

這是我在Go中的代碼：

type Data struct {
    Next string
    Results Result
}

type Result struct {
    Results []AreaGeometry
}

type AreaGeometry struct {
    AREAGEOMETRY_ID int32
    AreaManagerId int64
    AreaId string
    EndDateArea string
    StartDateArea string
    AreaGeometryTxt string
}

// Synchronizes the AreaGeometry in our MySQL database with the AreaGeometry in the database from the RDW
func retrieveData() {
    resp, err := http.Get("https://api.datamarket.azure.com/opendata.rdw/StatischParkeren.Open.Data/v1/AREAGEOMETRY?$format=json")
    if err != nil {
        panic(err.Error()) // TODO: proper error handling
    }
    body, err := ioutil.ReadAll(resp.Body)
    var d Data
    json.Unmarshal(body, &d)
    fmt.Println("Next: " + d.Next)
}

但是， d.Next在解組后返回一個空字符串。 我究竟做錯了什么？ 什么是Go的照顧方式？

Answer 1

您需要使用JSON注釋（在文檔中稱為struct“tags”）來讓它知道JSON中字段的名稱：

type Data struct {
    Next string `json:"__next"` //Field appears in JSON as key "__next".
    Results Result `json:"results"`
}

我相信Go會自動處理results與Results ，但如果你要發回數據並希望它是小寫的，你仍然需要注釋。

Results Result不正確 - 結果不是Result類型的對象，它是AreaGeometry的數組，因此它應如下所示：

type Data struct {
    Next string  `json:"__next"` //Field appears in JSON as key "__next".
    Results []AreaGeometry
}

此外，您需要JSON中的D對象的包裝器：

type D struct {
    D Data `json:"d"`
}


func main() {
    body := jsonString //too long to put here, but in the playground. 
    var d D
    err := json.Unmarshal([]byte(body), &d)
    if (err != nil) {
       fmt.Println(err)
    }
    fmt.Println("Next: " + d.D.Next)

}

http://play.golang.org/p/yK-zNxEMvy