java - 使用 API key 解析 JSON

Question

我是 JSON 和解析数据等方面的新手。我正在使用 GSON 并尝试拉取 JSONArray“系统”，然后显示 JSONObject 的“system_name”然后显示它。 下面是要拉取的 JSON 数据的示例。

 {
"systems": [
  {
  "city": "Petaluma",
  "country": "US",
  "postal_code": "94954",
  "state": "CA",
  "status": "normal",
  "system_id": 66,
  "system_name": "Smith Residence",
  "system_public_name": "Residential System",
  "timezone": "America/Los_Angeles"
},
{
  "city": "Atherton",
  "country": "US",
  "postal_code": "94954",
  "state": "CA",
  "status": "error",
  "system_id": 77,
  "system_name": "Jones Residence",
  "system_public_name": "Jones Residence",
  "timezone": "America/Los_Angeles"
}
 ]
}

API 使用 API_KEY 进行身份验证并像这样使用

https://api.company.com/api/systems?key=123ABC

代码

public class PullJSONData extends Activity {

TextView systemsTextView;
ProgressDialog progressDialog;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    systemsTextView = (TextView) findViewById(R.id.textView);

    this.retrieveSystems();
}
void retrieveSystems() {
    progressDialog = ProgressDialog.show(this, "Please wait...",
            "Retrieving data...", true, true);
    SystemsRetrieverAsyncTask task = new SystemsRetrieverAsyncTask();
    task.execute();
    progressDialog.setOnCancelListener(new CancelListener(task));
}

private class SystemsRetrieverAsyncTask extends AsyncTask<Void, Void, Void> {
    Response response;
    @Override
    protected Void doInBackground(Void... params) {
        String url = "https://api.company.com/api";
        HttpGet getRequest = new HttpGet(url);

        try {
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpResponse getResponse = httpClient.execute(getRequest);
            final int statusCode = getResponse.getStatusLine()
                    .getStatusCode();

            if (statusCode != HttpStatus.SC_OK) {
                Log.w(getClass().getSimpleName(), "Error " + statusCode
                        + " for URL " + url);
                return null;
            }

            HttpEntity getResponseEntity = getResponse.getEntity();
            InputStream httpResponseStream = getResponseEntity.getContent();
            Reader inputStreamReader = new InputStreamReader(
                    httpResponseStream);

            Gson gson = new Gson();
            SystemList systemList = gson.fromJson(jsonString, SystemList.class);

            for (int i = 0; i < systemList.systems.size(); i++)
            {
               System s = systemList.systems.get(i);
            }
            this.response = gson
                    .fromJson(inputStreamReader, Response.class);
        } catch (IOException e) {
            getRequest.abort();
            Log.w(getClass().getSimpleName(), "Error for URL " + url, e);
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);

        StringBuilder builder = new StringBuilder();
        for (System systems : this.response.data) {

            builder.append(String.format(
                    "<br>System: <b>%s</b><br>City: <b>%s</b><br><br>",
                    systems.getCountry(), systems.getCity()));

        }

        systemsTextView.setText(Html.fromHtml(builder.toString()));
        progressDialog.cancel();
    }

}

private class CancelListener implements OnCancelListener {

    AsyncTask<?, ?, ?> cancellableTask;

    public CancelListener(AsyncTask<?, ?, ?> task) {
        cancellableTask = task;
    }

    @Override
    public void onCancel(DialogInterface dialog) {
        cancellableTask.cancel(true);
    }

}

回应

public class Response {

ArrayList<System> data;

public Response() {
    data = new ArrayList<System>();
}

系统

public class System {

String city;
String country;

public System() {

    this.city = "";
    this.country = "";
}

public String getCity() {
    return this.city;
}

public String getCountry() {
    return this.country;
}

系统列表

public class SystemList {
public List<System> systems;

public SystemList() { systems = new ArrayList<System>(); }
}

如果您需要查看完整源代码，请查找 HERE

当前问题

• 空指针异常

• 来自 URL 的错误 401 https://api.company.com/api/systems/

  04-29 15:43:25.735: E/AndroidRuntime(3678): 致命异常: main 04-29 15:43:25.735: E/AndroidRuntime(3678): java.lang.NullPointerException 04-29 15:43:25.735:E/AndroidRuntime(3678):在 com.jaisonbrooks.enlightenme.PullJSONData$SystemsRetrieverAsyncTask.onPostExecute(PullJSONData.java:96) 04-29 15:43:25.735:E/AndroidRuntime(3678):在 com.jaisonbrooks.enlightenme.PullJSONData$SystemsRetrieverAsyncTask.onPostExecute(PullJSONData.java:1) 04-29 15:43:25.735: E/AndroidRuntime (3678): 在 android.os.AsyncTask.finish (AsyncTask.java:631) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 android.os.AsyncTask.access$600(AsyncTask.java:177) 04-29 15:43:25.735: E/AndroidRuntime (3678): 在 android.os.AsyncTask$InternalHandler.handleMessage (AsyncTask.java:644) 04-29 15:43:25.735: E/AndroidRuntime (3678): 在 android.os.Handler.dispatchMessage (Handler.java:99) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 android.os.Looper.loop(Looper.java:137) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 android.app.ActivityThread.main(ActivityThread.java:4898) 04-29 15:43:25.735:E/AndroidRuntime(3678):在 java.lang.reflect.Method.invokeNative( native 方法) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 java.lang.reflect.Method.invoke(Method.java:511) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773) 04-29 15:43:25.735: E/AndroidRuntime(3678): 在 dalvik.system.NativeStart.main(Native Method)

Answer 1

另一种选择(类似于上面的 jackson)是使用 Gson图书馆。在 json 处理方面做得很好。它也有很好的记录和理解。

编辑:

好的，在查看您的代码后，您似乎过度复杂化了 System 和 SystemList 类。

public class System {
    public String city;
    public String country;
    public String postal_code;
    public String state;
    public String status;
    public String system_id;
    public String system_name;
    public String system_public_name;
    public String timezone;
}

public class SystemsList {
    public List<System> systems;
}

您需要做的就是确保 json 中的名称映射到数据模型中的名称。

我还包含了一个完全通用的 GsonSerializer，这样它就可以重新用于其他 gson 响应

public class GsonSerializer 
{
private static final String TAG = "GsonSerializer";

public static <T> Object seralizeData (String response, T t)
{
    Gson serializer = new Gson();

    try 
    {
        return serializer.fromJson(response, t.getClass());
    } 
    catch (Exception e) 
    {
        e.printStackTrace();
        Logger.e(TAG, "deserialization failure: ".concat(response));
    }

    return null;
}

}

使用此类的方式如下。

 // Where mData is a class of type T
 mData = (T) GsonSerializer.seralizeData(Json, mData); 
 // or in a specific example
 mSystemList = (SystemList) GsonSerializer.seralizeData(Json, new SystemList());

这应该足以让您几乎可以即插即用。可能需要进行一些小调整。