从 JSON 获取数据？

Question

我想从中获取用户名 Json url。 我有这段代码，但它不能让我得到数据说

Json 解析错误

代码如下：

HttpHandler.java

public class HttpHandler {

private static final String TAG = HttpHandler.class.getSimpleName();

public HttpHandler() {
}

public String makeServiceCall(String reqUrl) {
    String response = null;
    try {
        URL url = new URL(reqUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        // read the response
        InputStream in = new BufferedInputStream(conn.getInputStream());
        response = convertStreamToString(in);
    } catch (MalformedURLException e) {
        Log.e(TAG, "MalformedURLException: " + e.getMessage());
    } catch (ProtocolException e) {
        Log.e(TAG, "ProtocolException: " + e.getMessage());
    } catch (IOException e) {
        Log.e(TAG, "IOException: " + e.getMessage());
    } catch (Exception e) {
        Log.e(TAG, "Exception: " + e.getMessage());
    }
    return response;
}

private String convertStreamToString(InputStream is) {
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();

    String line;
    try {
        while ((line = reader.readLine()) != null) {
            sb.append(line).append('\n');
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return sb.toString();
}
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

private String TAG = MainActivity.class.getSimpleName();

private ProgressDialog pDialog;
private ListView lv;

// URL to get contacts JSON
private static String url = "https://someLink";

ArrayList<HashMap<String, String>> contactList;

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

    contactList = new ArrayList<>();

    lv = (ListView) findViewById(R.id.list);

    new GetContacts().execute();
}

/**
 * Async task class to get json by making HTTP call
 */
private class GetContacts extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();

    }

    @Override
    protected Void doInBackground(Void... arg0) {
        HttpHandler sh = new HttpHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url);

        Log.e(TAG, "Response from url: " + jsonStr);

        if (jsonStr != null) {
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                JSONArray contacts = jsonObj.getJSONArray("");

                // looping through All Contacts
                for (int i = 0; i < contacts.length(); i++) {
                    JSONObject c = contacts.getJSONObject(i);

                    String name = c.getString("username");

                    // tmp hash map for single contact
                    HashMap<String, String> contact = new HashMap<>();

                    // adding each child node to HashMap key => value
                    contact.put("username", name);

                    // adding contact to contact list
                    contactList.add(contact);
                }
            } catch (final JSONException e) {
                Log.e(TAG, "Json parsing error: " + e.getMessage());
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Json parsing error: " + e.getMessage(),
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });

            }
        } else {
            Log.e(TAG, "Couldn't get json from server.");
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(getApplicationContext(),
                            "Couldn't get json from server. Check LogCat for possible errors!",
                            Toast.LENGTH_LONG)
                            .show();
                }
            });

        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        // Dismiss the progress dialog
        if (pDialog.isShowing())
            pDialog.dismiss();
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                MainActivity.this, contactList,
                R.layout.list_item, new String[]{"username"}, new int[]{R.id.name});

        lv.setAdapter(adapter);
    }

}
}

这是我在 google 上找到的一个示例，并尝试根据需要对其进行一些更改。我放了一个空的 JsonArray。我也尝试了其他示例，但我不明白出了什么问题。

**

>新问题

如果我的url是这样的？和其他的有什么区别？

**

Answer 1

您没有要在输出中解析的数组。你的 URL 给你一个对象。你的代码应该是这样的

    if (jsonStr != null) {
                    try {
                          JSONObject jsonObj = new JSONObject(jsonStr);
                          String name = jsonObj.getString("username");
                          //... now use the whereever you want
                          }
                        catch (final JSONException e) {
                         //... put your error log
                          }

Answer 2

请在 MainActivity 中编辑您的代码以从 json 字符串中获取 用户名，如下所示：

if(jsonStr!=null)
{
JSONObject jsonObj = new JSONObject(jsonStr); 
if(jsonObj !=null) 
{
String name = jsonObj .getString("username");
}
}

Answer 3

我建议你使用这个。

public class HttpGetResources extends AsyncTask<String, Void, Object> {

    @SuppressLint("StaticFieldLeak")
    private ProgressBar progressBar;
    private static final String RAW_DATE_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSSz";
    private String urlString;
    private String apiName;
    private Class Response_Class;
    private static final Gson GSON = new GsonBuilder().setDateFormat(RAW_DATE_FORMAT).create();
    private Context context;

    public HttpGetResources(Context context,Class Response_Class, String apiName, String urlString) {
        this.Response_Class = Response_Class;
        this.apiName = apiName;
        this.urlString = urlString;
        this.context=context;

    }


    @Override
    protected void onPreExecute() {
        super.onPreExecute();


    }

    @Override
    protected void onPostExecute(Object response) {
        super.onPostExecute(response);

    }
    HttpURLConnection conn = null;
    OutputStreamWriter out = null;
    Object result = null;
    BufferedReader buffer = null;
    final ExecutorService executor = Executors.newCachedThreadPool(Executors.defaultThreadFactory());
    static public Future<Object> future;

    @SuppressWarnings("unchecked")
    @Override
    protected Object doInBackground(final String... params) {

//      JsonObject res=null;

        future = executor.submit(new Callable<Object>() {
            @Override
            public Object call() throws IOException {

                try {
                    URL url = new URL(urlString + apiName);
                    conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("POST");
                    conn.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
                    conn.setConnectTimeout(3000);
                    conn.setReadTimeout(15000);
                    conn.setDoInput(true);
                    conn.setDoOutput(true);

                    out = new OutputStreamWriter(conn.getOutputStream());
                    out.write(params[0]);
                    out.flush();
                    out.close(); out=null;

                    buffer = new BufferedReader(new InputStreamReader(conn.getInputStream()));
//          res= GSON.fromJson(buffer, JsonObject.class);
//          result = new Gson().fromJson(res.toString(), Response_Class);


                    result = GSON.fromJson(buffer, Response_Class);
                    buffer.close(); buffer=null;

//          result = new Gson().fromJson(res.toString(), Response_Class);

                } catch (Exception e) {
                    //
                } finally {
                    if (buffer!=null) {
                        try {
                            buffer.close();
                        } catch (Exception e) { //
                        }
                    }
                    if (out != null) {
                        try {
                            out.close();
                        } catch (Exception e) { //
                        }
                    }
                    if (conn != null) {
                        conn.disconnect();
                    }
                }

                return result;
            }
        });

        try {
            result = future.get(10, TimeUnit.SECONDS);
        } catch (Exception ignored) {
        }
        return result;
    }
}

--以及调用方法--

public synchronized Object HttpGetRes(final Object REQUEST_CLASS, final Class RESPONSE_CLASS, final String
            API_NAME, final String URL) {
        if(isNetworkAvailable()) {
            response = null;
            try {
                Log.e(API_NAME, "url: " + URL);

                Log.e(REQUEST_CLASS.getClass().getSimpleName(), new Gson().toJson(REQUEST_CLASS));

                HttpGetResources resource = new HttpGetResources(BaseContext,RESPONSE_CLASS, API_NAME,
                        URL);
                response = resource.execute(new Gson().toJson(REQUEST_CLASS)).get();

            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }

            if (response != null) {
                String x = new Gson().toJson(response);
                Log.e(RESPONSE_CLASS.getSimpleName(), x);
                return response;
            } else {

            }
        }
            return null;
    }

Answer 4

以后尝试使用 GSON 库，它会自动为您自动将 JSON 对象转换为 java 对象。这对于避免解析复杂的 JSON 对象或 JSON 数组很有用。 https://github.com/google/gson