我有一个问题。我有一个 AsyncTaskActivity
类,其中包含通过 HttpURLConnection
与服务器 php 通信的方法 downloadUrl
。与 MySql DB 通信的服务器 php 应该根据元素的类型返回字符串文本或 json 格式的字符串。当服务器返回的元素类型是字符串文本时,HttpURLConnection
返回一个空字符串。
这是类 AsyncTaskActivity
。
public class AsyncTaskActivity extends AsyncTask<String, Void, String> {
private Context context;
String serverParameters;
public AsyncResponse delegate = null;
String url = null;
private ProgressDialog pd;
public AsyncTask(Context c, String s, AsyncResponse<String> delegate) {
this.serverParameters = s;
this.context = c;
this.delegate = delegate;
}
@Override
protected String doInBackground(String... strings) {
try {
url = downloadUrl(strings[0]);
} catch (IOException e) {
e.printStackTrace();
}
return url;
}
protected void onPreExecute() {
super.onPreExecute();
pd = new ProgressDialog(context);
pd.setTitle("Please Wait...");
pd.setMessage("Loading...");
pd.show();
}
protected void onPostExecute(String result) {
super.onPostExecute(result);
System.out.println("RESULT = " + result);
delegate.processFinish(result);
pd.dismiss();
}
private String downloadUrl(String targetURL) throws IOException {
URL url;
HttpURLConnection connection = null;
try {
// Create connection
url = new URL(targetURL);
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "application/json");
connection.setRequestProperty("Accept", "application/json");
connection.setUseCaches(false);
connection.setDoInput(true);
connection.setDoOutput(true);
// Send request
OutputStreamWriter wr = new OutputStreamWriter(connection.getOutputStream());
wr.write(serverParameters);
wr.flush();
wr.close();
// Get Response
InputStream is = connection.getInputStream();
String data = convertStreamToString(is);
is.close();
return data;
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
if (connection != null) {
connection.disconnect();
}
}
}
private String convertStreamToString(InputStream inputStream) {
Scanner s = new Scanner(inputStream).useDelimiter("\\A");
return s.hasNext() ? s.next() : "";
}
这是类 AvailabilityActivity
。当我向服务器发送请求时,必须指定为参数类型元素、访问类型(读取、写入、更改、删除)和要写入的 json。
在这种情况下,当我向服务器发送请求时(type element = "expertise", access = "read", json to write = ""),我得到一个空字符串。类型元素“expertise”应返回字符串文本。
在Riepilogo.setOnClickListener
serverParameters
初始化后,sendRequest()
执行AsyncTaskActivity()
。
public class AvailabilityActivity extends ActionBarActivity implements AsyncResponse<String> {
private Spinner spinner;
private Spinner spinner1;
/* Parameters Expertise*/
private static final String TIPO_ELEMENTO = "expertise";
private static final String ACCESSO = "read";
private AsyncTaskActivity send_request;
private String serverParameters;
private JSONObject jsonObject;
private ArrayList<String> list = new ArrayList<String>();
AvailabilityEntity availabilityEntity;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_availability);
spinner1 = (Spinner) findViewById(R.id.spinner1);
spinner = (Spinner) findViewById(R.id.spinner2);
Riepilogo.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
date_ = date.getText().toString();
startTime_ = startTime.getText().toString();
endTime_ = endTime.getText().toString();
timeEditText_ = timeEditText.getText().toString();
availabilityEntity = new AvailabilityEntity(date_, startTime_, endTime_, itemSpinner, timeEditText_);
showSummary();
}
});
serverParameters = generateParameters(TIPO_ELEMENTO, ACCESSO, "");
sendRequest();
}
private String generateParameters(String tipoElementoLogin, String accesso, String s) {
String parameters = "accesso:" + accesso + ", elemento:" + tipoElementoLogin + ", jsonDaScrivere:" + s;
return parameters;
}
private void sendRequest() {
send_request = new AsyncTaskActivityString(this, serverParameters, this);
send_request.execute(getApplicationContext().getResources().getString(R.string.serverQuery));
}
@Override
public void processFinish(String output) {
System.out.println("Value: " + output);
// Aggiunge lista expertise dal server in spinner
list.add(output);
ArrayAdapter<String> array_adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, list);
array_adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner1.setAdapter(array_adapter);
}
最佳答案
您似乎忘记调用 connection.connect()。 试试这段代码:
private String downloadUrl(String targetURL) throws IOException {
...
...
// Get Response
connection.connect();
int http_code = connection.getResponseCode();
String data = null;
if (http_code == HttpURLConnection.HTTP_OK) {
data = this.convertStreamToString(connection.getInputStream());
}
关于java - Android 返回空字符串 HTTP,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30918647/