java - 无法使用 Android 应用通过 API 下载数据

Question

我尝试通过 API 将应用程序与我的网站链接，但发生错误并且活动中未显示任何数据。它只显示一个包含数据的 Toast 消息和一个句子： (Toast.makeText(getApplicationContext(), "Json parsing error: " + e.getMessage(), Toast.LENGTH_LONG).show();

请帮我解决这个错误或给我任何改进它的提示

注意：我在互联网上找到的带有许可证 CC4 的代码，在修改之前它可以正常工作

谢谢

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".API.Other1_1.API_Test_1_1">

    <ListView
        android:id="@+id/list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    >
    <TextView
        android:id="@+id/Name"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="2dip"
        android:textColor="@color/colorAccent" />

    <TextView
        android:id="@+id/Roll"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#5d5d5d"
        android:textStyle="bold" />
</LinearLayout>

public class API_HttpHandler_1_1 {

    private static final String TAG = API_HttpHandler_1_1.class.getSimpleName();

    public API_HttpHandler_1_1() {
    }

    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();
    }
}

public class API_Test_1_1 extends AppCompatActivity {

    private String TAG = API_Test2.class.getSimpleName();
    private ListView lv;
    ArrayList<HashMap<String, String>> contactList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.api_test_1_1);

        contactList = new ArrayList<>();
        lv = (ListView) findViewById(R.id.list);

        new API_Test_1_1.GetContacts().execute();
    }

    private class GetContacts extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Toast.makeText(API_Test_1_1.this,"Json Data is downloading",Toast.LENGTH_LONG).show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {
            API_HttpHandler_1_1 sh = new API_HttpHandler_1_1();
            // Making a request to url and getting response
            String url = "http://klmop2-001-site1.gtempurl.com/api/Students";
            String jsonStr = sh.makeServiceCall(url);

            Log.e(TAG, "Response from url: " + jsonStr);
            if (jsonStr != null) {
                try {
                    //JSONObject jsonObj = new JSONObject(jsonStr);
                    JSONObject jsonObj = new JSONObject(jsonStr);

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

                    // looping through All Contacts
                    for (int i = 0; i < contacts.length(); i++) {
                        JSONObject c = contacts.getJSONObject(i);
                        //JSONArray c = contacts.getJSONArray(i);
                        String id = c.getString("ID");
                        String name = c.getString("Name");
                        String roll = c.getString("Roll");

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

                        // adding each child node to HashMap key => value
                        contact.put("ID", id);
                        contact.put("Name", name);
                        contact.put("Roll", roll);

                        // 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);
            ListAdapter adapter = new SimpleAdapter(API_Test_1_1.this, contactList,
                    R.layout.api_list_item_1_1, new String[]{ "Name","Roll"},
                    new int[]{R.id.Name, R.id.Roll});
            lv.setAdapter(adapter);
        }
    }
}

标签： javaandroidjsonapi