如何在字符串变量中获取特定的 Json 值 - Java？

Question

我有一个 Java 应用程序，它调用 evepraisal 的 API 来获取商品的特定“价格”： 这是我的代码：

String url =  "https://evepraisal.com/appraisal.json";
    URL obj = new URL(url);
    con = (HttpsURLConnection) obj.openConnection();

    //add reuqest header
    con.setRequestMethod("POST");
    con.setRequestProperty("User-Agent", "Mozilla/5.0");
   // con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");

    String urlParameters = "market=jita&raw_textarea=tritanium&persist=no&format=json";

    // Send post request
    con.setDoOutput(true);
    DataOutputStream wr = new DataOutputStream(con.getOutputStream());
    wr.writeBytes(urlParameters);
    wr.flush();
    wr.close();

    int responseCode = con.getResponseCode();
    System.out.println("\nSending 'POST' request to URL : " + url);
    System.out.println("Post parameters : " + urlParameters);
    System.out.println("Response Code : " + responseCode);

    BufferedReader in = new BufferedReader(
            new InputStreamReader(con.getInputStream()));
    String inputLine;
    StringBuffer response = new StringBuffer();

    JSONObject jsonObject = new JSONObject(response);



    String sellPrice = jsonObject.getJSONObject("totals").getString("sell");

    System.out.println("sell price " + sellPrice);

    while ((inputLine = in.readLine()) != null) {
        response.append(inputLine);
    }
    in.close();

    //print result
    System.out.println(response.toString());

控制台输出：

{
"appraisal":{
  "created":1582370316,
  "kind":"listing",
  "market_name":"jita",
  "totals":{
     "buy":7.09,
     "sell":7.29,
     "volume":0.01

},
  "items":[
     {
        "name":"tritanium",
        "typeID":34,
        "typeName":"Tritanium",
        "typeVolume":0.01,
        "quantity":1,
        "prices":{
           "all":{
              "avg":7.825135725671236,
              "max":6660,
              "median":8.49,
              "min":0.01,
              "percentile":10,
              "stddev":12.094503046356275,
              "volume":21067715118,
              "order_count":83

},
           "buy":{
              "avg":4.4427463532321685,
              "max":7.09,
              "median":5,
              "min":0.01,
              "percentile":7.01,
              "stddev":1.243253441213804,
              "volume":3668335637,
              "order_count":34

},
           "sell":{
              "avg":8.817038715163093,
              "max":6660,
              "median":8.49,
              "min":7.29,
              "percentile":7.32,
              "stddev":13.20791605306975,
              "volume":17399379481,
              "order_count":49

},
           "updated":"2020-02-22T11:16:22.644986932Z",
           "strategy":"orders"

我想把这个特定的值变成一个 String var : Appraisal --> total --> Sell = 7.29 我认为我的问题来自 getJSONObject 行。我在网上找到了多个教程，但没有一个能正确回答我的需求， 有时我有一个

Exception in thread "main" org.json.JSONException: JSONObject["totals"] not found.

参考

String sellPrice = jsonObject.getJSONObject("totals").getString("sell");

如果有人有滑雪道 我做错了什么？ 提前致谢

Answer 1

在您的代码中：

StringBuffer response = new StringBuffer();
JSONObject jsonObject = new JSONObject(response);

变量response 是空的，对吧？

试试这个：

JSONObject jsonObject = new JSONObject(response.toString());
jsonObject.getJSONObject("appraisal").getJSONObject("totals").getDouble("sell");

Answer 2

你可以试试这样的

JSONObject jsonObject = new JSONObject(response.toString());
double sell = (double)jsonObject.getJSONObject("appraisal").getJSONObject("totals")
              .getDouble("sell");