具有bufferedreader.readLine（）的缓冲区意外返回null

Question

I have problems using BufferedReader when I use readLine () it returns null value. This is my code:

How can I discover the source of the problem?

BackgroundTask_GET.java

public class BackgroundTask_GET extends AsyncTask<Void, Void, Void> {
String duongdan = MainActivity.SERVER_NAME;
TextView tvResult;
String strName, strScore;
String str;
ProgressDialog pDialog;
Context context;

public String TAG = "GG";

@Override
protected void onPreExecute() {
    super.onPreExecute();
    pDialog = new ProgressDialog(context);
    pDialog.setMessage("Sending...");
    pDialog.setIndeterminate(false);
    pDialog.setCancelable(false);
    pDialog.show();
}

public BackgroundTask_GET(Context context, TextView tvResult, String 
strName, String strScore) {
    this.tvResult = tvResult;
    this.strName = strName;
    this.strScore = strScore;
    this.context = context;
}

@Override
protected Void doInBackground(Void... voids) {
    duongdan += "?name=" + this.strName + "&score=" + this.strScore;
    try {
        URL url = new URL(duongdan);
        HttpURLConnection urlConnection = (HttpURLConnection) 
url.openConnection();
        BufferedReader bfr = new BufferedReader(new 
InputStreamReader(url.openStream()));
        String line = "";
        StringBuffer sb = new StringBuffer();
        Log.d(TAG, "bfr:" + urlConnection);
        while ((line = bfr.readLine()) != null) {
            sb.append(line);
            Log.d(TAG, "append"+sb.append(line));
        }
        str = sb.toString();
        urlConnection.disconnect();
        Log.d(TAG, "doInBackground: " + str);
    } catch (MalformedURLException e) {
        e.printStackTrace();
        Log.d(TAG, "exception " + e);
    } catch (IOException e) {
        e.printStackTrace();
        Log.d(TAG, "exception " + e);
    }
    return null;
}

@Override
protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);
    if (pDialog.isShowing()) {
        pDialog.dismiss();
    }
    tvResult.setText(str);
    Log.d("RESULT", "khanh" + str);
}

}

`` `MainActivity

public class MainActivity extends AppCompatActivity implements 
View.OnClickListener {
public static final String SERVER_NAME = 
"http://192.168.1.2/AndroidNetworking_server/student_GET.php";

private EditText edtName, edtScore;
private Button btnSend;
private TextView tvResult;

String strName, strScore;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    edtName = findViewById(R.id.edtName);
    edtScore = findViewById(R.id.edtScore);
    btnSend = findViewById(R.id.btnSend);
    tvResult = findViewById(R.id.tvResult);
    btnSend.setOnClickListener(this);
}

@Override
public void onClick(View view) {
    switch(view.getId()) {
        case R.id.btnSend:
            strName = edtName.getText().toString();
            strScore = edtScore.getText().toString();
            BackgroundTask_GET backgroundTask = new 
BackgroundTask_GET(this, tvResult, strName, strScore);
            backgroundTask.execute();
            break;
     }
   }
}

Error: ~

` 1 ` 2019-07-15 14:07:58.065 24764- 28936/com.example.lab2_khanhpd02377_androidnetworkingD/GG:bfr:com.android.okhttp.internal.huc.HttpURLConnectionImpl: http://192.168.1.2/AndroidNetworking_server/student_GET.php?name=4&score=5 ~

` 2 ` 2019-07-15 14:07:58.066 24764- 28936/com.example.lab2_khanhpd02377_androidnetworking D/GG: doInBackground:

Answer 1

I can see a couple of problems with your code:

1. The readLine() method returns the line with the line separator removed . So

    while ((line = bfr.readLine()) != null) { sb.append(line); } 

   will strip line separators while reading.

2. You are not checking the HTTP response code. If the response code is not a 2xx code, then getInputStream() will throw an exception.

   The response code can be found using getResponseCode() . The error response body can be read using getErrorStream() .

3. As @user207421 says, you shouldn't call urlConnection.disconnect() unless you really need to disconnect. If you don't need to, it is better to let the HTTP client library deal with disconnection. (It may be able to keep the connection open, and use it for later requests to the same server.)

4. You should ¹ close the BufferedReader , and ideally you should do it using try-with-resources .

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^{1 - I won't say must because there are scenarios where it won't matter. However, if you don't close the stream, one way or another, you will leak file descriptors which could lead to errors later on. And, it is certainly good practice to close streams ... because you never really know if your code might be used / reused in the future in some context where the resource leak does matter.}

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UPDATE - I think you are saying that the real real cause for the null / empty stream was on the PHP side. Notwithstanding that, you probably ought to address the four issues that I mentioned: line separators, response code, disconnect and using try-with-resource.