解析 openweatherMap json 文件

Question

我正在做一个需要获取天气信息的项目，所以我使用了 openweathermap api。我的程序正常工作，我从“main”和“wind”获取信息，但我还需要从主天气集获取描述。问题是天气集是 json 文件中的列表，我无法转换它映射。我试图解析的示例 json 文件是 http://api.openweathermap.org/data/2.5/weather?q=London

JSON：

{
   "coord":{
      "lon":-0.13,
      "lat":51.51
   },
   "weather":[
      {
         "id":803,
         "main":"Clouds",
         "description":"broken clouds",
         "icon":"04n"
      }
   ],
   "base":"stations",
   "main":{
      "temp":43.56,
      "pressure":1004,
      "humidity":87,
      "temp_min":41,
      "temp_max":46.4
   },
   "visibility":10000,
   "wind":{
      "speed":11.41,
      "deg":80
   },
   "rain":{

   },
   "clouds":{
      "all":75
   },
   "dt":1573350303,
   "sys":{
      "type":1,
      "id":1414,
      "country":"GB",
      "sunrise":1573369754,
      "sunset":1573402780
   },
   "timezone":0,
   "id":2643743,
   "name":"London",
   "cod":200
}

当我们查看文件时，我们注意到天气集中有一个 [] 括号，这在我的项目中造成了问题。我试图查找如何将列表投射到地图并尝试使用我的代码，但没有帮助。文件中的注释代码是我在尝试使其工作时尝试过的东西。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.HashMap;
import java.util.Map;

import com.google.gson.*;
import com.google.gson.reflect.*;
import java.util.List;
import java.lang.reflect.Type; 

import java.util.HashMap;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class PlantWateringApp {

    public static Map<String, Object> jsonToMap(String str) {

        Map<String, Object> map = new Gson().fromJson(str, new TypeToken<HashMap<String, Object>>() {
        }.getType());
        return map;
    }

    public static void main(String[] args) {

        String LOCATION = "delhi,india";
        String result = "{\"coord\":{\"lon\":77.22,\"lat\":28.65},\"weather\":[{\"id\":711,\"main\":\"Smoke\",\"description\":\"smoke\",\"icon\":\"50d\"}],\"base\":\"stations\",\"main\":{\"temp\":72.32,\"pressure\":1015,\"humidity\":59,\"temp_min\":64.4,\"temp_max\":77},\"visibility\":1000,\"wind\":{\"speed\":3.36,\"deg\":270},\"clouds\":{\"all\":0},\"dt\":1573351180,\"sys\":{\"type\":1,\"id\":9165,\"country\":\"IN\",\"sunrise\":1573348168,\"sunset\":1573387234},\"timezone\":19800,\"id\":1273294,\"name\":\"Delhi\",\"cod\":200}";
        System.out.println(result);

        Map<String, Object> respMap = jsonToMap(result.toString());
        Map<String, Object> mainMap = jsonToMap(respMap.get("main").toString());
        Map<String, Object> windMap = jsonToMap(respMap.get("wind").toString());

        // Type listType = new TypeToken<List<Map<String,String>>>()
        // {}.getType();
        // List<Map<String,String>> weatherMap = new
        // Gson().fromJson(respMap.get("description").toString(),listType);

        // Map<String, Object> name = (Map<String, Object>)
        // respMap.get("description");

        // Map<String, Object > weatherMap = jsonToMap
        // (respMap.get("description").toString());

        System.out.println("Location: " + LOCATION);
        System.out.println("Current Temperature: " + mainMap.get("temp"));
        System.out.println("Current Humidity: " + mainMap.get("humidity"));
        System.out.println("Max: " + mainMap.get("temp_min"));
        System.out.println("Min: " + mainMap.get("temp_max"));

        System.out.println("Wind Speed: " + windMap.get("speed"));
        System.out.println("Wind Angle: " + windMap.get("deg"));

    }
}

我尝试使用与 main 和 wind 相同的方式：Map weatherMap = jsonToMap (respMap.get("weather").toString());。但我遇到了错误：

////java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 3 path $[0]

所以我尝试不将 json 转换为 Map，而是直接使用像 Map weatherMap = (Map) respMap.get("weather"); 这样的地图，但我得到了

////java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map

为此，我尝试将列表投射到地图使用

              List<Map<String,String>> weatherMap = new Gson().fromJson(respMap.get("weather").toString(),listType);

但这说明：

//String cannot be converted to int

我真的很困惑在这种情况下该怎么做。我无法弄清楚如何处理 json 文件中的 []。

Answer 1

由于此数据以List 的形式提供，您正试图将其转换为Map。那是不对的。您需要将它（天气）作为地图列表，然后需要将每个元素视为地图。这是一个如何将其作为 Map

获取的示例

          ///...
          //// other code
          ///...      
          Map<String, Object > respMap = jsonToMap (result.toString());
          // don't need to convert from string to map again and again
          Map<String, Object > mainMap = (Map<String, Object >)respMap.get("main");
          Map<String, Object > windMap = (Map<String, Object >)respMap.get("wind");

          // fist get weather as list
          List<Map<String, Object >> weather = (List<Map<String, Object>>) (respMap.get("weather"));
            //...

          System.out.println("Wind Speed: " + windMap.get("speed")  );
          System.out.println("Wind Angle: " + windMap.get("deg")  );


          // weather as list
          System.out.println("Weather: "+ weather);

          // assuming weather contains at-least 1 element.
          Map<String, Object> weatherMap = weather.get(0);

          System.out.println("Weather as map: "+ weatherMap);

将其投射到列表中。

          List<Map<String, Object >> weather = (List<Map<String, Object>>) (respMap.get("weather"));

然后将每个元素视为 Map：

// assuming weather contains at-least 1 element.
          Map<String, Object> weatherMap = weather.get(0);

希望这会有所帮助。

Answer 2

让生活变得简单，使用真实的类型。

import java.util.List;

import com.google.gson.Gson;

public class PlantWateringApp {

    class Weather_2_5 {
        List<Weather> weather;
    }

    class Weather {
        Integer id;
        String main;
        String description;
        String icon;
    }

    public static void main(String[] args) {

        String result = "{\"coord\":{\"lon\":77.22,\"lat\":28.65},\"weather\":[{\"id\":711,\"main\":\"Smoke\",\"description\":\"smoke\",\"icon\":\"50d\"}],\"base\":\"stations\",\"main\":{\"temp\":72.32,\"pressure\":1015,\"humidity\":59,\"temp_min\":64.4,\"temp_max\":77},\"visibility\":1000,\"wind\":{\"speed\":3.36,\"deg\":270},\"clouds\":{\"all\":0},\"dt\":1573351180,\"sys\":{\"type\":1,\"id\":9165,\"country\":\"IN\",\"sunrise\":1573348168,\"sunset\":1573387234},\"timezone\":19800,\"id\":1273294,\"name\":\"Delhi\",\"cod\":200}";
        //System.out.println(result);

        Gson G = new Gson();
        Weather_2_5 obj = G.fromJson(result, Weather_2_5.class);

        for (int idx = 0; idx < obj.weather.size(); idx++) {
            System.out.println(obj.weather.get(idx).description);
        }
    }
}

Answer 3

您可以使用以下方式，而不是从头开始编写：

https://github.com/xSAVIKx/openweathermap-java-api

我认为这个例子最接近你想要做的：

https://github.com/xSAVIKx/openweathermap-java-api/blob/development/api-examples/src/main/java/org/openweathermap/api/example/CurrentWeatherOneLocationExample.java