无法从API响应中获取特定参数 [英] Having trouble getting specific parameter from API response
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问题描述
我正在尝试制作一个简单的天气应用.我正在为此使用此 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
I'm trying to make a simple weather app. I'm using this API for it. on that same page is a list of parameters in the JSON response. I can search for all the parameters and get a response except for the 'weather' parameter. every time I try that I get an
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.
error. I'm not sure what's causing it. here's my code.
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，为什么不能搜索天气参数?
I'm not really sure why that one parameter isn't working. I can search anything else fine, so why can't I search the weather parameter?
我在try/catch语句中执行此操作.给我一个NullPointerException
I'm doing this in my try/catch statement. it's giving me a 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);
推荐答案
不要盲目地将Hashmap作为键值，而应考虑创建pojos，然后对其进行解析. 为json创建所有PoJo.
Instead of blindly considering Hashmap for keyvalues, consider creating pojos, and then parse it. Create all PoJo for json.
Main.java
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)
Example.java (This pojo is for your json schema)
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
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
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
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
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
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;
}
}
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