Question

我正在尝试制作一个简单的天气应用。我正在使用this API。在同一页面上是JSON响应中的参数列表。我可以搜索所有参数，并获得“天气”参数以外的响应。每次尝试得到

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

错误。我不确定是什么原因造成的。这是我的代码。

public class Weather {

private String city;
private OWM owm = new OWM("8984d739fa91d7031fff0e84a3d2c520");
private CurrentWeather currentWeather;
private String weather;
private Clouds cloud;

public Weather() throws APIException {
    String API_KEY = "8984d739fa91d7031fff0e84a3d2c520";
    String Location = "Brooklyn";
    String urlString = "http://api.openweathermap.org/data/2.5/weather?q=" + Location
            + "&appid=" + API_KEY + "&units=imperial";

    try {
        StringBuilder result = new StringBuilder();
        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();
        BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String line;
        while ((line = rd.readLine()) != null){
            result.append(line);
        }
        rd.close();
        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());
        Map<String, Object> cloudsMap = jsonToMap(respMap.get("weather").toString());
// error is  here
        System.out.println("Current Temperature: " + mainMap.get("temp"));
        System.out.println("current humidity " + mainMap.get("humidity"));
        System.out.println("clouds " + respMap.get("description"));
      //  System.out.println("weather conditions: " + cloudsMap.get("main"));
// this always returns null 
        System.out.println("wind speeds " + windMap.get("speed"));
        System.out.println("wind angle: " + windMap.get("deg"));
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
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 String getCityName() {
    return cityName;
}
public int getCurrentWeather() throws APIException {
    owm.setUnit(OWM.Unit.IMPERIAL);
    currentWeather = owm.currentWeatherByCityName(this.cityName);
    return (int) Math.round(currentWeather.getMainData().getTemp());
}
public void setCityName(String cityName) {
    this.cityName = cityName;
}

public void setZipCode(String zipCode){
    this.zipCode = zipCode;
}
public String getZipCode(){
    return this.zipCode;
}
public String getWeather(){
    return this.weather;
}
}

我不太确定为什么该参数不起作用。我可以搜索其他任何东西，为什么我不能搜索天气参数？

编辑：我在try / catch语句中执行此操作。给我一个NullPointerException

URL url = new URL(urlString);
            URLConnection conn = url.openConnection();
            conn.connect();

            JsonParser jp = new JsonParser();
            JsonElement root = jp.parse(new InputStreamReader((InputStream) conn.getContent()));
            JsonObject rootObj = root.getAsJsonObject();
            String description = rootObj.get("weather").getAsString();
// name of the array in the json
            System.out.println(description);

Answer 1

Map<String, Object> cloudsMap = jsonToMap(respMap.get("weather").toString());

这是问题所在。您正在尝试将响应的weather属性解析为一个对象（一个Map），但实际上是一个数组。

Answer 2

在这里解析Json的最佳方法是Gson库首先，您可以在此处创建要获取的响应的pojo类，之后只需传递响应字符串并获取输出即可。

Gson gson=new Gson();
YourClass result=gson.fromjson(jsonString , YourClass.class);

Answer 3

不要盲目地将Hashmap作为键值，而应考虑创建pojo，然后对其进行解析。为json创建所有PoJo。

Main.java

public class Weather {

    public static void main(String[] args) {


    String API_KEY = "8984d739fa91d7031fff0e84a3d2c520";
    String Location = "Brooklyn";
    String urlString = "http://api.openweathermap.org/data/2.5/weather?q=" + Location
            + "&appid=" + API_KEY + "&units=imperial";

    try {
        StringBuilder result = new StringBuilder();
        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();
        BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String line;
        while ((line = rd.readLine()) != null){
            result.append(line);
        }
        rd.close();
        System.out.println(result);
        com.google.gson.Gson gson=new Gson();
        Example finalResult=gson.fromJson(result.toString() , Example.class);
        System.out.println(finalResult.getMain().getTemp()); //56.26
        System.out.println(finalResult.getMain().getHumidity());  // 54
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

Example.java（此pojo用于您的json模式）

import java.util.List;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Example {

@SerializedName("coord")
@Expose
private Coord coord;
@SerializedName("weather")
@Expose
private List<Weather> weather = null;
@SerializedName("base")
@Expose
private String base;
@SerializedName("main")
@Expose
private Main main;
@SerializedName("visibility")
@Expose
private Integer visibility;
@SerializedName("wind")
@Expose
private Wind wind;
@SerializedName("clouds")
@Expose
private Clouds clouds;
@SerializedName("dt")
@Expose
private Integer dt;
@SerializedName("sys")
@Expose
private Sys sys;
@SerializedName("timezone")
@Expose
private Integer timezone;
@SerializedName("id")
@Expose
private Integer id;
@SerializedName("name")
@Expose
private String name;
@SerializedName("cod")
@Expose
private Integer cod;

public Coord getCoord() {
return coord;
}

public void setCoord(Coord coord) {
this.coord = coord;
}

public List<Weather> getWeather() {
return weather;
}

public void setWeather(List<Weather> weather) {
this.weather = weather;
}

public String getBase() {
return base;
}

public void setBase(String base) {
this.base = base;
}

public Main getMain() {
return main;
}

public void setMain(Main main) {
this.main = main;
}

public Integer getVisibility() {
return visibility;
}

public void setVisibility(Integer visibility) {
this.visibility = visibility;
}

public Wind getWind() {
return wind;
}

public void setWind(Wind wind) {
this.wind = wind;
}

public Clouds getClouds() {
return clouds;
}

public void setClouds(Clouds clouds) {
this.clouds = clouds;
}

public Integer getDt() {
return dt;
}

public void setDt(Integer dt) {
this.dt = dt;
}

public Sys getSys() {
return sys;
}

public void setSys(Sys sys) {
this.sys = sys;
}

public Integer getTimezone() {
return timezone;
}

public void setTimezone(Integer timezone) {
this.timezone = timezone;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Integer getCod() {
return cod;
}

public void setCod(Integer cod) {
this.cod = cod;
}

}

Coord.java


import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Coord {

@SerializedName("lon")
@Expose
private Double lon;
@SerializedName("lat")
@Expose
private Double lat;

public Double getLon() {
return lon;
}

public void setLon(Double lon) {
this.lon = lon;
}

public Double getLat() {
return lat;
}

public void setLat(Double lat) {
this.lat = lat;
}

}

Weather.java

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Weather {

@SerializedName("id")
@Expose
private Integer id;
@SerializedName("main")
@Expose
private String main;
@SerializedName("description")
@Expose
private String description;
@SerializedName("icon")
@Expose
private String icon;

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getMain() {
return main;
}

public void setMain(String main) {
this.main = main;
}

public String getDescription() {
return description;
}

public void setDescription(String description) {
this.description = description;
}

public String getIcon() {
return icon;
}

public void setIcon(String icon) {
this.icon = icon;
}

}

Main.java

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Main {

@SerializedName("temp")
@Expose
private Double temp;
@SerializedName("pressure")
@Expose
private Integer pressure;
@SerializedName("humidity")
@Expose
private Integer humidity;
@SerializedName("temp_min")
@Expose
private Integer tempMin;
@SerializedName("temp_max")
@Expose
private Double tempMax;

public Double getTemp() {
return temp;
}

public void setTemp(Double temp) {
this.temp = temp;
}

public Integer getPressure() {
return pressure;
}

public void setPressure(Integer pressure) {
this.pressure = pressure;
}

public Integer getHumidity() {
return humidity;
}

public void setHumidity(Integer humidity) {
this.humidity = humidity;
}

public Integer getTempMin() {
return tempMin;
}

public void setTempMin(Integer tempMin) {
this.tempMin = tempMin;
}

public Double getTempMax() {
return tempMax;
}

public void setTempMax(Double tempMax) {
this.tempMax = tempMax;
}

}

Wind.java

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Wind {

@SerializedName("speed")
@Expose
private Double speed;
@SerializedName("deg")
@Expose
private Integer deg;

public Double getSpeed() {
return speed;
}

public void setSpeed(Double speed) {
this.speed = speed;
}

public Integer getDeg() {
return deg;
}

public void setDeg(Integer deg) {
this.deg = deg;
}

}

Clouds.java

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Clouds {

@SerializedName("all")
@Expose
private Integer all;

public Integer getAll() {
return all;
}

public void setAll(Integer all) {
this.all = all;
}

}

Sys.java

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Sys {

@SerializedName("type")
@Expose
private Integer type;
@SerializedName("id")
@Expose
private Integer id;
@SerializedName("message")
@Expose
private Double message;
@SerializedName("country")
@Expose
private String country;
@SerializedName("sunrise")
@Expose
private Integer sunrise;
@SerializedName("sunset")
@Expose
private Integer sunset;

public Integer getType() {
return type;
}

public void setType(Integer type) {
this.type = type;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public Double getMessage() {
return message;
}

public void setMessage(Double message) {
this.message = message;
}

public String getCountry() {
return country;
}

public void setCountry(String country) {
this.country = country;
}

public Integer getSunrise() {
return sunrise;
}

public void setSunrise(Integer sunrise) {
this.sunrise = sunrise;
}

public Integer getSunset() {
return sunset;
}

public void setSunset(Integer sunset) {
this.sunset = sunset;
}

}

无法从API响应获取特定参数

3 个答案: