Gson to Plain旧Java对象（PO​​JO）

Question

我已阅读GSon用户指南并查看了一些关于此处的问题，但我非常努力地理解为什么我在尝试使用GSon创建java对象时出现错误

public class TestJSON extends ActionBarActivity { 
    private Location start; 
    private String length; 
    private String url = "http://maps.googleapis.com/maps/api/directions/json?origin="; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_test_json); 

     // dummyprovider is provided by google to let me set a location. 
     start = new Location("dummyprovider"); 
     start.setLatitude(51.5033630); 
     start.setLongitude(-0.1276250); 

     // Recieve an android warning if you run a retrieval task (such as JSON) 
     // in the main thread). 
     try { 
      System.out.println("printing Json"); 

      Thread thread = new Thread(new Runnable() { 
       @Override 
       public void run() { 
        try { 

         toJava(readJsonFromUrl(urlBuilder())); 
        } catch (Exception e) { 
         e.printStackTrace(); 
        } 
       } 
      }); 
      thread.start(); 

     } catch (Exception e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.test_json, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 
     if (id == R.id.action_settings) { 
      return true; 
     } 
     return super.onOptionsItemSelected(item); 
    } 

    // I think in future I will call this function a ton of times and send it 
    // some locations as waypoints for it to try and get closer to the 
    // distances. 
    private String urlBuilder() { 
     String newUrl = url + start.getLatitude() + "," + start.getLongitude() 
       + "&destination=51.5042178,23"; 

     return newUrl; 
    } 

    // Builds the string for JSON. 
    private String readAll(Reader rd) throws IOException { 
     StringBuilder sb = new StringBuilder(); 
     int cp; 
     while ((cp = rd.read()) != -1) { 
      sb.append((char) cp); 
     } 
     return sb.toString(); 
    } 

    // Take an input url and reads from it using the url above. We then put it 
    // into a JSON object. 
    private JSONObject readJsonFromUrl(String url) throws IOException, 
      JSONException { 
     InputStream is = new URL(url).openStream(); 
     try { 
      BufferedReader rd = new BufferedReader(new InputStreamReader(is, 
        Charset.forName("UTF-8"))); 
      String jsonText = readAll(rd); 
      JSONObject json = new JSONObject(jsonText); 

      return json; 
     } finally { 
      is.close(); 
     } 
    } 

    private void toJava(JSONObject obj) throws Exception { 
     Gson gson = new Gson(); 
     MapsRoute m = gson.fromJson(readJsonFromUrl(urlBuilder()).toString(), 
       MapsRoute.class); 
     System.out.println(m); 

    } 

    } 

MapsRoute.java

public class MapsRoute { 

     @SerializedName("routes") 
     public List<String> routes; 

     @SerializedName("copyrights") 
     public String copyrights; 

     @SerializedName("legs") 
     public List<String> legs; 

     @SerializedName("steps") 
     public List<String> steps; 

    } 

这是堆栈跟踪

09-24 19:22:47.367: W/System.err(1720): com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 27 
09-24 19:22:47.367: W/System.err(1720):  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:176) 
09-24 19:22:47.367: W/System.err(1720):  at com.google.gson.Gson.fromJson(Gson.java:803) 
09-24 19:22:47.367: W/System.err(1720):  at com.google.gson.Gson.fromJson(Gson.java:768) 
09-24 19:22:47.367: W/System.err(1720):  at com.google.gson.Gson.fromJson(Gson.java:717) 
09-24 19:22:47.367: W/System.err(1720):  at com.google.gson.Gson.fromJson(Gson.java:689) 
09-24 19:22:47.367: W/System.err(1720):  at boyle.matt.runrouter.TestJSON.toJava(TestJSON.java:119) 
09-24 19:22:47.367: W/System.err(1720):  at boyle.matt.runrouter.TestJSON.access$2(TestJSON.java:117) 
09-24 19:22:47.371: W/System.err(1720):  at boyle.matt.runrouter.TestJSON$1.run(TestJSON.java:47) 
09-24 19:22:47.371: W/System.err(1720):  at java.lang.Thread.run(Thread.java:856) 
09-24 19:22:47.371: W/System.err(1720): Caused by: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 27 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.stream.JsonReader.nextString(JsonReader.java:821) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:358) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:346) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) 
09-24 19:22:47.371: W/System.err(1720):  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) 
09-24 19:22:47.371: W/System.err(1720):  ... 8 more 

我确定我误解了一些简单的东西，非常感谢您的指导。

这是它试图分析的谷歌地图网址，我成功接收它，因为我可以在我的readfromurl方法中将它系统化。

http://maps.googleapis.com/maps/api/directions/json?origin=51.5033630,-0.1276250&destination=51.5042178,23

编辑：这是调用readsFromUrl当输出（urlBuilder（））;

09-24 19：57：03.879：I /的System.out（4068）： { “状态”： “OK”， “路由”：[{ “waypoint_order，其中”： []，“摘要“：”A2“，”bounds“：{”southwest“：{”lng“： - 0.1262498，”lat“：50.91870669999999}， ”northeast“：{”lng“：23.0020594，”lat“：52.4304362}}， “腿”：[{“duration”：{“value”：63803，“text”：“17 小时43分钟”}，“distance”：{“value”：1825694，“text”：“1,826 km” }， “END_LOCATION”：{ “LNG”：23.0020594， “LAT”：51.50389209999999}， “START_ADDRESS”： “70 白厅，伦敦

SW1A 2AS，英国”， “END_ADDRESS”：“Orzechów-科洛尼亚2， 21-109 Orzechów-Kolonia， Poland“，”start_location“：{”lng“： - 0.1262498，”lat“：51.5034032}，”via_waypoint“：[]，”steps“：[{”html_instructions“：”Head north </b> on Whitehall/Whitehall/A3212 </b>朝 Horse Guards Ave </b>“，”duration“：{”value“：17，”text“：”1 min“}，distance “：{”value“：157，”text“：”0.2 km“}，”end_location“：{”lng“： - 0.1265332，”lat“：51.50479920000001}”polyline“：{”points“”ggjyH tW]@cADYD[DUBWFy@PWD"},"travel_mode":"DRIVING","start_location":{"lng":-0.1262498,"lat":51.5034032}},{"html_instructions":"Turn <b>right<\/b> onto <b>Horse Guards Ave<\/b>","duration":{"value":53,"text":"1 min"},"distance":{"value":242,"text":"0.2 km"},"end_location":{"lng":-0.1231268,"lat":51.50464890000001},"polyline":{"points":"_pjyHxuWC]Ei@IgAAQAOAMAK?OAK?M?M?K?I?I@I?M@S @wEPeBBY“}，”start_location“：{”lng“： - 0.1265332，”lat“：51.50479920000001}，”机动“：”右转“，”travel_mode“：”DRIVING“}，{”html_instructions“转 右</b>驶入维多利亚 路堤/ A3211 </b>“，”duration“：{”value“：49，”text“：”1距离“：{”value“：389，”text“：”0.4 km“}，”end_location“：{”lng“： - 0.1239744，”lat“：51.5011942}，”polyline“： {“points”：“aojyHp WxH~Ab@H En @〜@F @？b @ Bl @@”}，“start_location”：{“lng”： - 0.1231268，“lat”：51.50464890000001}，“机动”：“右转“，”travel_mode“：”DRIVING“}，{”html_instructions“：”转 离开</b>转入威斯敏斯特桥路/ A302 </b>离开收费区</div>进入收费区 区</，“duration”：{“value”：62，“text”：“1 min”}，“distance”：{“value”：507，“text”：“0.5 km”}，“end_location” “LNG”： - 0.1170572， “LAT”：51.50053550000001}， “折线”：{ “点”：“myiyHxeW @ ABABCB DADCBABCBC @ CBEBIķ| E @ģ@ @@ GBW} @@ @ QA q因子@ DkFFkF？？？？ KFuAFgAEYC @ @@克的iA _ @ö@ú@ Q因子@ KBMBGBGP [FM “}，” START_LOCATION “：{” LNG “： - 0.1239744，”[艾@？]？LAT“：51。5011942}，“机动”：“左转”，“travel_mode”：“驾驶”}，{“html_instructions”：“稍微 离开</b>留在威斯敏斯特桥路/ A302 </b>离开收费 区域</div>“，”duration“：{”value“：4，”text“：”1 min“}，”distance“：{”value“：26，”text“：”26 m“} “END_LOCATION”：{ “LNG”： - 0.1167459， “LAT”：51.5004276}， “折线”：{ “点”： “kuiyHrzUFIBEBG @ģ@ģ@克间？”}， “START_LOCATION”：{ “LNG” ：-0.1170572，“lat”：51.50053550000001}，“机动”：“左转轻微”，“travel_mode”：“驾驶”}，{“html_instructions”：“转 左</b>留在威斯敏斯特桥“{”value“：4，”text“：” min“}米 “}，” end_loca重刑 “：{” LNG “： - 0.1165272，” LAT “：51.5005834}，” 折线 “：{” 点 “：” utiyHtxUIQIMIK “}，” START_LOCATION “：{” LNG “： - 0.1167459，” LAT“：51.5004276} ，“机动”：“左转”，“travel_mode”：“驾驶”}，{“html_instructions”：“稍微 右</b>留在威斯敏斯特桥 Rd/A302 </b>”， “：{”value“：10，”text“：”1 min“}，”distance“：{”value“：52，”text“：”52 m“}，”end_location“：{”lng“ ：-0.1158714， “LAT”：51.5007879}， “折线”：{ “点”： “suiyHhwUEa @ GUGQQc @ AE G G？”}， “START_LOCATION”：{ “LNG”： - 0.1165272， “LAT”：51.5005834 }，“maneuver”：“turn-slight-right”，“travel_mode”：“DRIVING”}，{“html_instructions”：“转 右</b>留在威斯敏斯特桥路/ A302 </b>按照威斯敏斯特桥 Rd </div> Ente电话号码 区域</div>“，”duration“：{”value“：93，”text“：”2 mins“}，”distance“：{”value“：848，”text“：”0.8 公里 “}，” END_LOCATION “：{” LNG “： - 0.1051152，” LAT “：51.49874029999999}，” 折线 “：{” 点 “：”} viyHdsU @ EBG | E @ CBEBCFGNQBMFMLYZm @ b @ö@ d @Ò@ FUDKd @ oAXe @ Vs的@〜@ ICN [DKFKDGBGJYb @ _B \ mBRiAHa @ BO @我？g | E？g @ @@ UBE] CMAOIyAAo @·K·G·EGyAAe @ EoAIwCKyCEoAAa @ GiBIc @ CQCW “}，” START_LOCATION” ：{ “LNG”： - 0.1158714， “LAT”：51.5007879}， “演习”： “转右”， “TRAVEL_MODE”：“DR

Answer 1

嘿Java对象与JSON的映射是不妥当的。

示例：路线具有边界，腿，版权，步骤，而不是它在上述代码中映射的方式。