json通过gson解析返回null [英] json parsing through gson returning null

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问题描述

我正在解析 json 来自 OpenWeathermap.org 就是这样的： 

  {
cod：200，
message：0.0016，
city：{
id：1164408，
name ：美元：
coord：{
lon：68.857384，
lat：27.70516 
}，
国家：PK ，
population：0，
sys：{
population：0 
}}，
 
cnt：2， 
list：[
 {
dt：1394175600，
temp：{
day：26.31，
min ：20，
max：30.17，
晚上：22.71，
前夕：30.17，
早晨：20 
}，
压力：1024.11，
湿度：59，
天气：[
 {
id：801，
main： 云，
描述：少云，
图标： 02d

]，
速度：0.91，
deg：121，
云：12 
}，
 $ bdt：1394262000，
temp：{
day：25.58，
min：18.94，
max： 28.22，
夜晚：21.08，
前夕：28.22，
早晨：18.94 
}，
压力：1026.39，
湿度：58，
天气：[
 {
id：800，
main：Clear，
description ：天空晴朗，
icon：01d
} 
]，
速度：5.75，
deg：74，
云：0 
} 
]}

在这个 SO问题中，我让我的 Model.java class for json 数据为

  public class Model {
 
 protected S tring cityId = null; 
 protected String cityName = null; 
保护字符串countryName = null; 
 protected String longitude = null; 
 protected String latitude = null; 
 protected String polution = null; 
 protected List< ForecatList> forcastList = null; 
 // getters setters 
 public class ForecatList {
 protected String dayTimeTemp = null; 
保护字符串maxTemp = null; 
保护字符串minTemp = null; 
保护字符串nightTimeTemp = null; 
保护字符串eveTimeTemp = null; 
保护字符串mornTimeTemp = null; 
 protected String pressure = null; 
保护字符串湿度=空; 
 protected String windSpeed = null; 
 protected String WindDegree = null; 
 protected String clouds = null; 
保护清单<天气> weathers = null; 
 // getters setters 
 public class Weather {
 protected String weatherId = null; 
 protected String weatherCondition = null; 
 protected String weatherDescription = null; 
保护字符串weatherIcon = null; 
 // getters setters 
} 
}}

解析专家是： 

  public Model getForecastByCityName（Context context，String city，int ofDays）{
 Model model = null; 
尝试{
 Gson gson = new Gson（）; 
 Reader reader = new InputStreamReader（forecastByCityName（context，city，ofDays））; 
 model = gson.fromJson（reader，Model.class）; 
返回模型; 
} catch（ClientProtocolException e）{
 e.printStackTrace（）; 
返回null; 
} catch（IOException e）{
 e.printStackTrace（）; 
返回null; 
 
 
 $ / code $ / pre 
 $ b 
和 forecastByCityName（） / code>是：
 
 pre $ private $ InputStream forecastByCityName 
 HttpClient httpClient = null; 
 StringBuilder url = new StringBuilder（URL_FORCAST）; 
 url.append（city）; 
 url.append（String.valueOf（ofDays））; 
 url.append（UNIT）; 
 HttpGet httpRequest = new HttpGet（url.toString（））; 
 httpClient = new DefaultHttpClient（）; 
 HttpResponse httpResponse = httpClient.execute（httpRequest）; 
 int statusCode = httpResponse.getStatusLine（）。getStatusCode（）; 
 if（statusCode == 200）{
 HttpEntity httpEntity = httpResponse.getEntity（）; 
 return httpEntity.getContent（）; 
} else {
 return null; 
} 
}

我的请求已成功，但是当我尝试获取模型对象的值：

$ p $ textView.setText（model.getCityName （）+ model.getCountryName（））;

打印 null null null ，为什么未能获得值？任何想法..

解决方案


  1. Model类中的所有字段名称必须相同json keys：for国家 - 受保护的字符串国家;

  2. 城市json键具有自己的内部数据，因此您需要创建具有适当字段名称的City类并定义'protected City city'字段在您的Model类中。

您需要的全部内容（100％适用于您的json示例）：

  public class Model实现Serializable {
 
私有字符串cod; 
私人双重信息; 
私人城市城市; 
私人整数cnt; 
私人列表< ListItem> list = new ArrayList< ListItem>（）; 
 
 public String getCod（）{
 return cod; 
} 
 
 public void setCod（String cod）{
 this.cod = cod; 
} 
 
 public Double getMessage（）{
 return message; 
} 
 
 public void setMessage（Double message）{
 this.message = message; 
} 
 
 public City getCity（）{
 return city; 
} 
 
 public void setCity（City city）{
 this.city = city; 
} 
 
 public Integer getCnt（）{
 return cnt; 
} 
 
 public void setCnt（Integer cnt）{
 this.cnt = cnt; 
} 
 
 public List< ListItem> getList（）{
 return list; 
} 
 
 public void setList（List< ListItem> list）{
 this.list = list; 
} 
 
 private class City实现Serializable {
 private Integer id; 
私人字符串名称; 
 @SerializedName（coord）
私人坐标坐标; 
私人字符串国家; 
私人整数人口; 
 private Sys sys; 
 
 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; 
} 
 
公共坐标getCoordinates（）{
返回坐标; 
} 
 
 public void setCoordinates（坐标坐标）{
 this.coordinates = coordinates; 
} 
 
 public String getCountry（）{
 return country; 
} 
 
 public void setCountry（String country）{
 this.country = country; 
} 
 
 public Integer getPopulation（）{
 return population; 
} 
 
 public void setPopulation（Integer population）{
 this.population = population; 
} 
 
 public Sys getSys（）{
 return sys; 
} 
 
 public void setSys（Sys sys）{
 this.sys = sys; 
} 
 
 private class Coordinates实现Serializable {
 @SerializedName（lon）
 private double经度; 
 @SerializedName（lat）
私人双纬度; 
 
 public Double getLongitude（）{
 return longitude; 
} 
 
 public void setLongitude（Double Longitude）{
 this.longitude = longitude; 
} 
 
 public Double getLatitude（）{
 return latitude; 
} 
 
 public void setLatitude（Double latitude）{
 this.latitude = latitude; 
} 
} 
 
私人类Sys实现Serializable {
私有Integer人口; 
 
 public Integer getPopulation（）{
 return population; 
} 
 
 public void setPopulation（Integer population）{
 this.population = population; 
 
 
 
 $ b private class ListItem实现Serializable {
 @SerializedName（dt）
 private long dateTime; 
 @SerializedName（temp）
 private温度温度; 
私人双重压力; 
私人整数湿度; 
私人列表<天气> weather = new ArrayList< Weather>（）; 
私人双倍速度; 
 @SerializedName（deg）
私人整数程度; 
私人整数云; 
 
 public Long getDateTime（）{
 return dateTime; 
} 
 
 public void setDateTime（Long dateTime）{
 this.dateTime = dateTime; 
} 
 
 public温度getTemperature（）{
 return temperature; 
} 
 
 public void setTemperature（温度温度）{
 this.temperature = temperature; 
} 
 
 public Double getPressure（）{
 return pressure; 
} 
 
 public void setPressure（Double pressure）{
 this.pressure = pressure; 
} 
 
 public Integer getHumidity（）{
 return humidity; 
} 
 
 public void setHumidity（Integer humidity）{
 this.humidity = humidity; 
} 
 
公共列表< Weather> getWeather（）{
 return weather; 
} 
 
 public void setWeather（List< Weather> weather）{
 this.weather = weather; 
} 
 
 public Double getSpeed（）{
 return speed; 
} 
 
 public void setSpeed（Double speed）{
 this.speed = speed; 
} 
 
 public Integer getDegree（）{
 return degree; 
} 
 
 public void setDegree（Integer degree）{
 this.degree = degree; 
} 
 
 public Integer getClouds（）{
 return clouds; 
} 
 
 public void setClouds（Integer clouds）{
 this.clouds = clouds; 
} 
 
 private class Temperature实现Serializable {
 private double day; 
私人双人分钟; 
私人双人最大; 
私人双晚; 
 @SerializedName（eve）
私人双人晚上; 
 @SerializedName（morn）$​​ b $ b私人双早; 
 
 public Double getDay（）{
 return day; 
} 
 
 public void setDay（Double Day）{
 this.day = day; 
} 
 
 public Double getMin（）{
 return min; 
} 
 
 public void setMin（Double min）{
 this.min = min; 
} 
 
 public Double getMax（）{
 return max; 
} 
 
 public void setMax（Double max）{
 this.max = max; 
} 
 
 public Double getNight（）{
 return night; 
} 
 
 public void setNight（Double night）{
 this.night = night; 
} 
 
 public double getEvening（）{
 return evening; 
} 
 
 public void setEvening（Double evening）{
 this.evening = evening; 
} 
 
 public Double getMorning（）{
 return morning; 
} 
 
 public void setMorning（Double morning）{
 this.morning = morning; 
} 
} 
 
 private class Weather implements Serializable {
 private Integer id; 
 private String main; 
私有字符串描述; 
私人字符串图标; 
 
 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; 
} 
} 
}

}


I'm parsing json data from OpenWeathermap.org which is like this :

{
   "cod":"200",
"message":0.0016,
"city":{
  "id":1164408,
  "name":"Sukkur",
  "coord":{
     "lon":68.857384,
     "lat":27.70516
  },
  "country":"PK",
  "population":0,
  "sys":{
     "population":0
  }  },  

"cnt":2,
"list":[
  {
     "dt":1394175600,
     "temp":{
        "day":26.31,
        "min":20,
        "max":30.17,
        "night":22.71,
        "eve":30.17,
        "morn":20
     },
     "pressure":1024.11,
     "humidity":59,
     "weather":[
        {
           "id":801,
           "main":"Clouds",
           "description":"few clouds",
           "icon":"02d"
        }
     ],
     "speed":0.91,
     "deg":121,
     "clouds":12
  },
  {
     "dt":1394262000,
     "temp":{
        "day":25.58,
        "min":18.94,
        "max":28.22,
        "night":21.08,
        "eve":28.22,
        "morn":18.94
     },
     "pressure":1026.39,
     "humidity":58,
     "weather":[
        {
           "id":800,
           "main":"Clear",
           "description":"sky is clear",
           "icon":"01d"
        }
     ],
     "speed":5.75,
     "deg":74,
     "clouds":0
  }
]}

after looking at thisSO Question, I made my Model.java class for above json data as 

public class Model{

protected String cityId = null;
protected String cityName = null;
protected String countryName = null;
protected String longitude = null;
protected String latitude = null;
protected String polution = null;
protected List<ForecatList> forcastList = null;
// getters setters
public class ForecatList {
    protected String dayTimeTemp = null;
    protected String maxTemp = null;
    protected String minTemp = null;
    protected String nightTimeTemp = null;
    protected String eveTimeTemp = null;
    protected String mornTimeTemp = null;
    protected String pressure = null;
    protected String humidity = null;
    protected String windSpeed = null;
    protected String WindDegree = null;
    protected String clouds = null;
    protected List<Weather> weathers = null;
    // getters setters
    public class Weather {
        protected String weatherId = null;
        protected String weatherCondition = null;
        protected String weatherDescription = null;
        protected String weatherIcon = null;
        // getters setters
    }
}}

parsing profess is :

public Model getForecastByCityName(Context context, String city, int ofDays){
    Model model = null;     
    try {           
        Gson gson = new Gson();
        Reader reader = new InputStreamReader(forecastByCityName(context, city, ofDays));           
        model = gson.fromJson(reader, Model.class);         
        return model;
    } catch (ClientProtocolException e) {
        e.printStackTrace();
        return null;
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }   
}

and forecastByCityName() is :

private InputStream forecastByCityName(Context context, String city, int ofDays) throws ClientProtocolException, IOException{
    HttpClient httpClient = null;
    StringBuilder url = new StringBuilder(URL_FORCAST);
    url.append(city);
    url.append(String.valueOf(ofDays));
    url.append(UNIT);
    HttpGet httpRequest = new HttpGet(url.toString());
    httpClient = new DefaultHttpClient();
    HttpResponse httpResponse = httpClient.execute(httpRequest);
    int statusCode = httpResponse.getStatusLine().getStatusCode();
    if (statusCode == 200) {
        HttpEntity httpEntity = httpResponse.getEntity();
        return httpEntity.getContent();
    }else {
        return null;            
    }       
}

my request is successful, but when I try to get values from Model object like :

textView.setText(model.getCityName() + model.getCountryName());

that prints null null null, why that fails to get values? any idea..

解决方案

  1. All field names in Model class must be equal json keys: for "country" - protected String country;
  2. "city" json key has its own inner data, so you need to create City class with appropriate field names and to define 'protected City city;' field in your Model class.

Here all you need (100 % works on your json-example):

public class Model implements Serializable {

private String cod;
private Double message;
private City city;
private Integer cnt;
private List<ListItem> list = new ArrayList<ListItem>();

public String getCod() {
    return cod;
}

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

public Double getMessage() {
    return message;
}

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

public City getCity() {
    return city;
}

public void setCity(City city) {
    this.city = city;
}

public Integer getCnt() {
    return cnt;
}

public void setCnt(Integer cnt) {
    this.cnt = cnt;
}

public List<ListItem> getList() {
    return list;
}

public void setList(List<ListItem> list) {
    this.list = list;
}

private class City implements Serializable { 
    private Integer id;
    private String name;
    @SerializedName("coord")
    private Coordinates coordinates;
    private String country;
    private Integer population;
    private Sys sys;

    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 Coordinates getCoordinates() {
        return coordinates;
    }

    public void setCoordinates(Coordinates coordinates) {
        this.coordinates = coordinates;
    }

    public String getCountry() {
        return country;
    }

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

    public Integer getPopulation() {
        return population;
    }

    public void setPopulation(Integer population) {
        this.population = population;
    }

    public Sys getSys() {
        return sys;
    }

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

    private class Coordinates implements Serializable {
        @SerializedName("lon")
        private Double longitude;
        @SerializedName("lat")
        private Double latitude;

        public Double getLongitude() {
            return longitude;
        }

        public void setLongitude(Double longitude) {
            this.longitude = longitude;
        }

        public Double getLatitude() {
            return latitude;
        }

        public void setLatitude(Double latitude) {
            this.latitude = latitude;
        }
    }

    private class Sys implements Serializable {
        private Integer population;

        public Integer getPopulation() {
            return population;
        }

        public void setPopulation(Integer population) {
            this.population = population;
        }
    }
}

private class ListItem implements Serializable {
    @SerializedName("dt")
    private Long dateTime;
    @SerializedName("temp")
    private Temperature temperature;
    private Double pressure;
    private Integer humidity;
    private List<Weather> weather = new ArrayList<Weather>();
    private Double speed;
    @SerializedName("deg")
    private Integer degree;
    private Integer clouds;

    public Long getDateTime() {
        return dateTime;
    }

    public void setDateTime(Long dateTime) {
        this.dateTime = dateTime;
    }

    public Temperature getTemperature() {
        return temperature;
    }

    public void setTemperature(Temperature temperature) {
        this.temperature = temperature;
    }

    public Double getPressure() {
        return pressure;
    }

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

    public Integer getHumidity() {
        return humidity;
    }

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

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

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

    public Double getSpeed() {
        return speed;
    }

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

    public Integer getDegree() {
        return degree;
    }

    public void setDegree(Integer degree) {
        this.degree = degree;
    }

    public Integer getClouds() {
        return clouds;
    }

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

    private class Temperature implements Serializable {
        private Double day;
        private Double min;
        private Double max;
        private Double night;
        @SerializedName("eve")
        private Double evening;
        @SerializedName("morn")
        private Double morning;

        public Double getDay() {
            return day;
        }

        public void setDay(Double day) {
            this.day = day;
        }

        public Double getMin() {
            return min;
        }

        public void setMin(Double min) {
            this.min = min;
        }

        public Double getMax() {
            return max;
        }

        public void setMax(Double max) {
            this.max = max;
        }

        public Double getNight() {
            return night;
        }

        public void setNight(Double night) {
            this.night = night;
        }

        public Double getEvening() {
            return evening;
        }

        public void setEvening(Double evening) {
            this.evening = evening;
        }

        public Double getMorning() {
            return morning;
        }

        public void setMorning(Double morning) {
            this.morning = morning;
        }
    }

    private class Weather implements Serializable {
        private Integer id;
        private String main;
        private String description;
        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;
        }
    }
}

}

这篇关于json通过gson解析返回null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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