Gson预计BEGIN_OBJECT，但是STRING

Question

我使用wunderground获取我的Java Web应用程序的天气信息。 经过一番搜索后，我发现Gson看起来像一个很好的json解析器。

但下面的一些例子，我似乎无法弄清楚如何跳过根元素。 这里是一个预测JSON请求的例子：

{ 
    "forecast" : { 
     "simpleforecast" : { 
      "forecastday" : [ { 
       "avehumidity" : 61, 
       "avewind" : { 
        "degrees" : 342, 
        "dir" : "NNW", 
        "kph" : 11, 
        "mph" : 7 
       }, 
       "conditions" : "Clear", 
       "date" : { 
        "ampm" : "PM", 
        "day" : 17, 
        "epoch" : "1358478000", 
        "hour" : 21, 
        "isdst" : "0", 
        "min" : "00", 
        "month" : 1, 
        "monthname" : "January", 
        "pretty" : "9:00 PM CST on January 17, 2013", 
        "sec" : 0, 
        "tz_long" : "America/Chicago", 
        "tz_short" : "CST", 
        "weekday" : "Thursday", 
        "weekday_short" : "Thu", 
        "yday" : 16, 
        "year" : 2013 
       }, 
       "high" : { 
        "celsius" : "11", 
        "fahrenheit" : "52" 
       }, 
       "icon" : "clear", 
       "icon_url" : "http://icons-ak.wxug.com/i/c/k/clear.gif", 
       "low" : { 
        "celsius" : "-2", 
        "fahrenheit" : "28" 
       }, 
       "maxhumidity" : 76, 
       "maxwind" : { 
        "degrees" : 340, 
        "dir" : "NNW", 
        "kph" : 18, 
        "mph" : 11 
       }, 
       "minhumidity" : 38, 
       "period" : 1, 
       "pop" : 10, 
       "qpf_allday" : { 
        "in" : 0.0, 
        "mm" : 0.0 
       }, 
       "qpf_day" : { 
        "in" : 0.0, 
        "mm" : 0.0 
       }, 
       "qpf_night" : { 
        "in" : 0.0, 
        "mm" : 0.0 
       }, 
       "skyicon" : "mostlysunny", 
       "snow_allday" : { 
        "cm" : 0, 
        "in" : 0 
       }, 
       "snow_day" : { 
        "cm" : 0, 
        "in" : 0 
       }, 
       "snow_night" : { 
        "cm" : 0, 
        "in" : 0 
       } 
      }, 
      { 
       "avehumidity" : 59, 
       "avewind" : { 
        "degrees" : 172, 
        "dir" : "South", 
        "kph" : 6, 
        "mph" : 4 
       }, 
       "conditions" : "Clear", 
       "date" : { 
        "ampm" : "PM", 
        "day" : 18, 
        "epoch" : "1358564400", 
        "hour" : 21, 
        "isdst" : "0", 
        "min" : "00", 
        "month" : 1, 
        "monthname" : "January", 
        "pretty" : "9:00 PM CST on January 18, 2013", 
        "sec" : 0, 
        "tz_long" : "America/Chicago", 
        "tz_short" : "CST", 
        "weekday" : "Friday", 
        "weekday_short" : "Fri", 
        "yday" : 17, 
        "year" : 2013 
       }, 
       "high" : { 
        "celsius" : "10", 
        "fahrenheit" : "50" 
       }, 
       "icon" : "clear", 
       "icon_url" : "http://icons-ak.wxug.com/i/c/k/clear.gif", 
       "low" : { 
        "celsius" : "-1", 
        "fahrenheit" : "30" 
       }, 
       "maxhumidity" : 84, 
       "maxwind" : { 
        "degrees" : 170, 
        "dir" : "South", 
        "kph" : 10, 
        "mph" : 6 
       }, 
       "minhumidity" : 40, 
       "period" : 2, 
       "pop" : 0, 
       "qpf_allday" : { 
        "in" : 0.0, 
        "mm" : 0.0 
       }, .................. 

现在我只关心的部分是forecastday。所以我所做的是以下几点：

package entity.json; 

import java.util.List; 

public class Data { 
    private List<Forecast> forecastday; 

    public List<Forecast> getForecastdays() { 
     return forecastday; 
    } 
} 

预测类：

package entity.json; 

public class Forecast { 
    private int avehumidity; 
    private Avewind avewind; 
    private String conditions; 
    private DateWeather date; 
    private CelciusHigh high; 
    private String icon_url; 
    private CelciusLow low; 
    // + constructor, getters, setters 

这里是我的方法：

public void createWeatherForecast(){ 
     String text = ""; 
     try { 
      URL url = new URL(jsonUrl); 
      System.out.println(jsonUrl); 
      Scanner s = new Scanner(url.openStream()); 
      while(s.hasNextLine()){ 
       text += s.nextLine(); 
      } 
      Data weather = new Gson().fromJson(text, Data.class); 
      System.out.println(new Gson().toJson(weather)); 
      System.out.println(weather.getForecastdays().get(0).getAvewind()); 
     } catch (IOException ex) { 
      Logger.getLogger(WeatherController.class.getName()).log(Level.SEVERE, null, ex); 
     } 
    } 

现在我应该也可以侧重于预测， simpleforecast？

Answer 1

仅仅因为你在JSON对象中的一部分“只关心”并不能使GSON能够魔术般地提供;）

要么你需要让你的POJO相匹配的JSON对象，或者编写一个自定义的反序列化器，丢弃你不感兴趣的JSON对象的部分并返回你的Data类的一个实例。