java – 解析JSON时获取NullPointerException

发布时间：2020-12-15 01:02:41 所属栏目：Java 来源：网络整理

导读：对我来说一切看起来都是正确的：获取结果对象,获取系列数组,获取索引处的对象,以及获取数据数组. private void downloadAllData() throws JSONException { queryApi(); JSONObject results = mJsonResponse.getJSONObject("Results"); // NullPointerExcepti

对我来说一切看起来都是正确的：获取结果对象,获取系列数组,获取索引处的对象,以及获取数据数组.

private void downloadAllData() throws JSONException {

    queryApi();

    JSONObject results = mJsonResponse.getJSONObject("Results"); // NullPointerException here
    JSONArray seriesArray = results.getJSONArray("series");

    JSONObject DataSeries1 = seriesArray.getJSONObject(0);
    JSONArray DataArray1 = DataSeries.getJSONArray("data");

    JSONObject DataSeries2 = seriesArray.getJSONObject(1);
    JSONArray DataArray2 = DataSeries.getJSONArray("data");

JSON提要：

{"status":"REQUEST_SUCCEEDED","responseTime":36,"message":[],"Results":{
"series":
[{"seriesID":"431432","data":[{"year":"1977","period":"M12","periodName":"December","value":"160.7","footnotes":[{}]},{"year":"1977","period":"M11","periodName":"November","value":"161.3","period":"M10","periodName":"October","value":"162.2","period":"M09","periodName":"September","value":"162.5","period":"M08","periodName":"August","value":"163.4","period":"M07","periodName":"July","value":"164.0","period":"M06","periodName":"June","value":"164.6","period":"M05","periodName":"May","value":"165.8","period":"M04","periodName":"April","value":"166.7","period":"M03","periodName":"March","value":"167.9","period":"M02","periodName":"February","value":"169.1","period":"M01","periodName":"January","value":"170.6","footnotes":[{}]}]},{"seriesID":"321432","value":"50.5","value":"50.4","value":"50.6","value":"50.1","value":"49.4","value":"48.8","value":"48.3","value":"47.6","footnotes":[{}]}]}]
}}

logcat的：

04-10 22:16:59.519  10910-10937/com.learn.kent.mojito E/AndroidRuntime﹕ FATAL EXCEPTION: IntentService[DownloadService]
    Process: com.learn.kent.mojito,PID: 10910
    java.lang.NullPointerException
            at com.learn.kent.mojito.service.DownloadService.downloadAllData(DownloadService.java:151)
            at com.learn.kent.mojito.service.DownloadService.onHandleIntent(DownloadService.java:83)
            at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.os.HandlerThread.run(HandlerThread.java:61)

04-10 22:16:59.659  10910-10910/com.learn.kent.mojito D/OpenGLRenderer﹕ 
Enabling debug mode 0
04-10 22:16:59.729  10910-10910/com.learn.kent.mojito I/ActivityManager﹕ Timeline: Activity_idle id: android.os.BinderProxy@42db38a8 time:59558459
04-10 22:17:00.369  10910-10910/com.learn.kent.mojito D/DownloadService﹕ {"Results":{"series":[{"data":[{"value":"50.5","year":"1977","footnotes":[{}],"periodName":"December"},{"value":"50.4","periodName":"November"},{"value":"50.5","periodName":"October"},{"value":"50.6","periodName":"September"},"periodName":"August"},"periodName":"July"},"periodName":"June"},{"value":"50.1","periodName":"May"},{"value":"49.4","periodName":"April"},{"value":"48.8","periodName":"March"},{"value":"48.3","periodName":"February"},{"value":"47.6","periodName":"January"}],"seriesID":"21432"},{"data":[{"value":"62.1",{"value":"61.9",{"value":"61.6",{"value":"61.4",{"value":"61.2",{"value":"61.0",{"value":"60.7",{"value":"60.3",{"value":"60.0",{"value":"59.5",{"value":"59.1",{"value":"58.5","seriesID":"431432"}]},"status":"REQUEST_SUCCEEDED","responseTime":44}
04-10 22:17:01.489  10910-10937/com.learn.kent.mojito I/Process﹕ Sending signal. PID: 10910 SIG: 9

logcat中的JSON响应表示log.d(TAG,mJsonResponse.tostring)

使用Volley初始化mJsonResponse：

private void queryApi() throws JSONException {
        try {
            jsonObjectQuery.put("seriesid",seriesid);
            jsonObjectQuery.put("startyear","" + startYear);
            jsonObjectQuery.put("endyear","" + endYear);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        JsonObjectRequest jsonObjRequest = new JsonObjectRequest(Request.Method.POST,url,jsonObjectQuery,new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                mJsonResponse = response; <--------------------------------
                Log.d(TAG,mJsonResponse.toString());
            }
        },new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
            }
        }) {

            @Override
            public Map<String,String> getHeaders() throws AuthFailureError {
                HashMap<String,String> headers = new HashMap<String,String>();
                headers.put("Content-Type","application/json; charset=utf-8");
                return headers;
            }
        };
        queue.add(jsonObjRequest);
    }

解决方法

异步任务导致此错误.你必须确保mJsonResponse =响应;在JSONObject结果= mJsonResponse.getJSONObject(“Results”);之前调用.喜欢：

public void onResponse(JSONObject response) {
    mJsonResponse = response; <--------------------------------
    Log.d(TAG,mJsonResponse.toString());
    JSONObject results = mJsonResponse.getJSONObject("Results"); // NullPointerException here
    JSONArray seriesArray = results.getJSONArray("series");

    JSONObject DataSeries1 = seriesArray.getJSONObject(0);
    JSONArray DataArray1 = DataSeries.getJSONArray("data");

    JSONObject DataSeries2 = seriesArray.getJSONObject(1);
    JSONArray DataArray2 = DataSeries.getJSONArray("data");
}

（编辑：李大同）

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