使用GSON解析JSON时获取NullPointerException

Question

我尝试使用GSON库解析JSON。参考。我使用的链接：link

json文件：

{"Details": [{"EndDate": "01/11/2013 05:10:00","Type": "Numeric", "StartDate": "12/12/2012 04:00:00", "UTCDate": "12/31/2012 07:55:01", "Min": "1000.00", "ConvertedStartDate": "12/12/2012 04:00:00", "ConvertedUTCDate": "12/31/2012 07:55:01", "Name": "User Car Auction", "Max": "3000.00", "ConvertedEndDate": "01/11/2013 05:10:00" }], "result": [{ "AllowtoComment": false, "Rank": 1, "Low": "5000.00", "DetailsID": 51, "ItemDetails": {"ID": 28, "SpecificationFile": "", "ItemDescription": "Pristine White accord. 176K miles. Runs Great", "ImageName": "http://64.151.125.199/Auction/28/Desert.jpg", "ItemName": "1986 Honda Accord"}, "Desc": "Pristine White accord. 176K miles. Runs Great", "Comment": "<null>", "DetailsID": 78, "Name": "1986 Honda Accord", "LowRank": 1 }, { "AllowtoComment": false, "Rank": 1, "Low": "7000.00", "DetailsID": 52, "ItemDetails": {"ID": 28, "SpecificationFile": "", "ItemDescription": "Black w/Tan Interior. 110K Miles. New tires", "ImageName": "http://64.151.125.199/Auction/28/Penguins.jpg", "ItemName": "1989 Isuzu Trooper"}, "Desc": "Black w/Tan Interior. 110K Miles. New tires", "Comment": "N/A", "DetailsID": 100, "Name": "1989 Isuzu Trooper", "LowRank": 1 }]}

ItemDetails.java

public class ItemDetails {

   public int ID;

   public String SpecificationFile;

   public String ItemDescription;

   public String ImageName;

   public String ItemName;
}

Result.java

public class Result {

   public boolean AllowtoComment;

   public int Rank;

   public String Low;

   public int DetailsID;

   public boolean ShowCompetingBid;

   public ItemDetails itemDetails;

   public String Desc;

   public String Comment;

   public int DetailsID;

   public String Name;

   public int LowRank;
}

Detail.java

public class Detail {

   public String EndDate;

   public String Type;

   public String StartDate;

   public String UTCDate;

   public String Min;

   public String ConvertedStartDate;

   public String ConvertedUTCDate;

   public String Name;

   public String Max;

   public String ConvertedEndDate;

 }

Responce.java

public class Responce {

   public List<Detail> details;
   public List<Result> results;
}

主要Java代码

 public class GsonParsingActivity extends Activity {

private ProgressBar bgProcess;
private String SERVER = "url";

private String TAG = "LargeJSON";

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_gson);

    bgProcess = (ProgressBar) findViewById(R.id.progressBarGson);

    new GetDetail().execute();
}

private class GetDetail extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        bgProcess.setVisibility(View.VISIBLE);
    }

    @Override
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub

        try {
            Map<String, String> mMap = new HashMap<String, String>();
            mMap.put("ID", "28");
            mMap.put("ParticipantID", "2");
            mMap.put("CompanyID", "5");

            InputStream source = getDataForSimpleMap(SERVER + "getList",
                    mMap);

            Gson gson = new Gson();

            Reader reader = new InputStreamReader(source);

            AuctionResponce responce = gson.fromJson(reader,
                    Responce.class);

            List<Result> results = responce.results;

            Log.d(TAG, ">>>>>>>>>>>>>> " + results.size());

            for (Result result : results) {
                Log.v(TAG, " ==================> "+ result.BidDetailsID);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        bgProcess.setVisibility(View.INVISIBLE);
    }
}

@SuppressWarnings("rawtypes")
private InputStream getDataForSimpleMap(String strURL,
        Map<String, String> params) {
    try {
        // JSONObject jArray = null;

        InputStream stream = null;

        Iterator iterator = params.entrySet().iterator();

        JSONObject data = new JSONObject();

        while (iterator.hasNext()) {
            Map.Entry mEntry = (Map.Entry) iterator.next();
            String key = mEntry.getKey().toString();
            String value = mEntry.getValue().toString();
            data.put(key, value);
        }

        stream = getJSONFromURL(strURL, data);

        return stream;

    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

private InputStream getJSONFromURL(String strURL, JSONObject data) {
    try {
        InputStream stream = null;

        HttpClient httpClient = new DefaultHttpClient();

        HttpConnectionParams.setConnectionTimeout(httpClient.getParams(),
                120000);

        HttpPost httpPost = new HttpPost(strURL);

        httpPost.setHeader("content-type", "application/json");

        if (data != null) {
            StringEntity entity = new StringEntity(data.toString(),
                    HTTP.UTF_8);

            httpPost.setEntity(entity);
        }

        HttpResponse response = null;

        response = httpClient.execute(httpPost);

        if (response != null) {
            stream = response.getEntity().getContent();
        } else {
            stream = null;
        }

        return stream;
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}
}

但不幸的是我收到了以下错误：

02-11 12:10:01.075: W/System.err(587): java.lang.NullPointerException
02-11 12:10:01.094: W/System.err(587):  at com.example.largejson.GsonParsingActivity$GetAuctionDetail.doInBackground(GsonParsingActivity.java:80)
02-11 12:10:01.094: W/System.err(587):  at com.example.largejson.GsonParsingActivity$GetAuctionDetail.doInBackground(GsonParsingActivity.java:1)
02-11 12:10:01.094: W/System.err(587):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
02-11 12:10:01.094: W/System.err(587):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
02-11 12:10:01.105: W/System.err(587):  at java.util.concurrent.FutureTask.run(FutureTask.java:138)
02-11 12:10:01.105: W/System.err(587):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
02-11 12:10:01.115: W/System.err(587):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
02-11 12:10:01.115: W/System.err(587):  at java.lang.Thread.run(Thread.java:1019)