Develop Reference

Return the content of a text file on localhost

I am trying to return the content of a text file on localhost (wamp server) as a string. I can read the text file but I cannot return a string because the function run of Runnable is a void. I'm working on Android Studio (that's why I'm using thread).
public String serverToString()
{
String str;
Thread t = new Thread(new Runnable() {
public void run() {
try {
URL url = new URL("http://myIP/test.txt");
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
str = in.readLine();
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Throwable th) {
th.printStackTrace();
}
}
});
t.start();
return str;
}

Advancing the the Cricket answer, I usually create an AsyncTask and inside it I define a callback interface.
The activity executing this task should implements this interface.
As an example of part of the code:
public class TeamUpdateTask extends AsyncTask, Object, TeamUpdateResponse> {
private TeamUpdateTaskCallback mListener;
#Override
public void onPostExecute (TeamUpdateResponse result) {
if (exception == null) {
mListener.OnTeamUpdateCompleted(result);
} else {
processException();
}
}
public void setListener (TeamUpdateTaskCallback listener) {
mListener = listener;
}
public interface TeamUpdateTaskCallback {
void OnTeamUpdateCompleted (TeamUpdateResponse response);
}
}
Hope it helps.

Generally, Volley library would be preferred over raw Thread. Or AsyncTask
but I cannot return a string because the function run of Runnable is a void
You can pass the result to a new method, though.
Define an interface
public interface ServerResponse {
void onResponse(String msg);
}
Add a parameter
public void serverToString(final ServerResponse callback)
{
String str;
Thread t = new Thread(new Runnable() {
public void run() {
try {
URL url = new URL("http://myIP/test.txt");
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
callback.onResponse(in.readLine()); // This is the 'return' now
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Throwable th) {
th.printStackTrace();
}
}
});
t.start();
}
And instead of this
String response = serverToString();
Do this
serverToString(new ServerResponse() {
#Override
public void onResponse(String response) {
// handle message
}
});

JAVA: How to listen to calling of event handler/How to get returned result of an event handler?

I am creating an Android chat application wherein I am using WebSockets and on top of that I want to create a custom implementation of Application protocol.
I am stuck in a situation.
Essentially, what I want is a way to know that an event handler method has been called in another class, fire up my own method in my class based on that and then get the result of that event handler method in my class.
How is that possible?
I researched a lot and found something like binding, event emitters, etc. Can someone point me to the right direction and provide some resources from where I can learn this technique?
This is what I have done so far:
public void connect(){
try {
setUpWebSocketHandler(handler);
mConnection.connect(wsuri, handler);
}
catch (WebSocketException e) {
Log.d("exception", e.toString());
}
}
public void setUpWebSocketHandler(WebSocketHandler handler)
{
handler = new WebSocketHandler(){
//first method for websockethandler
#Override
public void onOpen() {
//here i create a json format string to be sent to my server that returns something afterwards
String output = json.toString();
Log.d("OUTPUT+" , output);
Log.d("onOpen", "Status: Connected to " + wsuri);
mConnection.sendTextMessage(output);
}
//second method for websockethandler
#Override
public void onTextMessage(final String payload) {
Log.d("onTextMessage", "Response: " + payload);
JSONObject jsonObj = null;
try {
jsonObj = new JSONObject(payload);
} catch (JSONException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
String type = jsonObj.getString("type");
switch (type) {
case "xxx":
//authEvent
System.out.println("xxx");
break;
case "yyy":
//userOnlineEvent
System.out.println("yyy");
break;
case "zzz":
System.out.println("zzz");
break;
case "userListToken":
userList = getUserList(payload);
break;
default:
System.out.println("DefaultCase");
break;
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//third method for websockethandler
#Override
public void onClose(int code, String reason) {
Log.d("onClose", "Connection lost.");
}
};
}
public String getUserList(final String payload)
{
final Thread connectthread;
connectthread = new Thread(
new Runnable()
{
public void run()
{
try {
//here i create a URL, send post request to it and i get a response with userlist
HttpClient client = new DefaultHttpClient();
HttpGet post = new HttpGet(url);
HttpResponse response = client.execute(post);
BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
while ((userList = rd.readLine()) != null) {
System.out.println(userList);
Log.d("HTTP GET RESPONSE", "Response: " + userList);
}
} catch (JSONException | IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
);
connectthread.start();
try
{
connectthread.join();
}
catch (Exception e)
{
Log.i("error","Error!!");
}
System.out.println("userListToken");
return userList;
}
I have another question. I got the userList using callbacks....The problem now is:
private class ProcessLogin extends AsyncTask<String, Void, String> {
private ProgressDialog pDialog;
String uname,password;
#Override
protected void onPreExecute() {
super.onPreExecute();
uname = txtUsername.getText().toString();
password = txtPassword.getText().toString();
pDialog = new ProgressDialog(LoginActivity.this);
pDialog.setTitle("Contacting Servers");
pDialog.setMessage("Logging in ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
#Override
protected String doInBackground(String... args) {
String user = null;
ifly.connect();
user = userList;
return user;
}
#Override
protected void onPostExecute(String user) {
try {
if(user != null){
//Intent i = new Intent("com.example.tabmainactivity");
Log.d("Got it", "Response: " + userList);
pDialog.dismiss();
//startService(new Intent(getApplicationContext(),iFlyChatMessage.class));
//startActivity(i);
//finish();
}else{
// username / password doesn't match
pDialog.dismiss();
Toast.makeText(getApplicationContext(),
"Incorrect username/password", Toast.LENGTH_SHORT).show();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
public void processMessage(String userList)
{
this.userList = userList;
}
I want the userList in postExecute so that i can send this userList to another activity. How do i stop doinbackground() to wait for callback to finish. If I use thread.sleep, the whole process stops, not even connect works.
Thanks

You can declare an interface somewhere, make your event handler accept an instance of this interface, then create an anonymous class implementing this interface while passing that instance in your handler's registration with event source.
Something like below:
public class MyClass{
...
...
component.addXXXListener(new EventHandler(new MyInterface() {
#Override
public void doSomething() {
callMethod();
}
}));
...
...
public void callMethod() {
...
...
}
I hope you got the point.

I'm not sure that I understood you correctly.
You should use callback object.
Something like:
public interface MessageProcesor{
public void processMessage(String message);
}
Your activity should implement this interface.
And you should have MessageProcesor field in your "client" class.
Your code should look something like this:
private MessageProcesor callback;
public void setUpWebSocketHandler(WebSocketHandler handler)
{
handler = new WebSocketHandler(){
//first method for websockethandler
#Override
public void onOpen() {
//here i create a json format string to be sent to my server that returns something afterwards
String output = json.toString();
Log.d("OUTPUT+" , output);
Log.d("onOpen", "Status: Connected to " + wsuri);
mConnection.sendTextMessage(output);
}
//second method for websockethandler
#Override
public void onTextMessage(final String payload) {
Log.d("onTextMessage", "Response: " + payload);
JSONObject jsonObj = null;
try {
jsonObj = new JSONObject(payload);
} catch (JSONException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
String type = jsonObj.getString("type");
switch (type) {
case "xxx":
//authEvent
System.out.println("xxx");
break;
case "yyy":
//userOnlineEvent
System.out.println("yyy");
break;
case "zzz":
System.out.println("zzz");
break;
case "userListToken":
userList = getUserList(payload);
callback.processMessage(userList);
break;
default:
System.out.println("DefaultCase");
break;
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//third method for websockethandler
#Override
public void onClose(int code, String reason) {
Log.d("onClose", "Connection lost.");
}
};
}
public String getUserList(final String payload)
{
final Thread connectthread;
connectthread = new Thread(
new Runnable()
{
public void run()
{
try {
//here i create a URL, send post request to it and i get a response with userlist
HttpClient client = new DefaultHttpClient();
HttpGet post = new HttpGet(url);
HttpResponse response = client.execute(post);
BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
while ((userList = rd.readLine()) != null) {
System.out.println(userList);
Log.d("HTTP GET RESPONSE", "Response: " + userList);
}
} catch (JSONException | IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
);
connectthread.start();
try
{
connectthread.join();
}
catch (Exception e)
{
Log.i("error","Error!!");
}
System.out.println("userListToken");
return userList;
}
You can pass "callback" as constructor param or via setter method.
Hope this helps.

Performance of Android using HttpClient with Apache server running php scripts with Memcache

I have an application in which an Android device is connected to a data acquisition system and the data is stored in a local db. I want to monitor in real time the data on a second Android as well. In order to enhance performance, I set up my own Apache server (XAMPP) on a Windows machine. I wrote two php scripts; one to store data in Memcache and one to get data from memcache. The Android devices are using HttpClient to call the scripts. I used memcache in order to eliminate some delays of writing to database. Below is the code used for sending and receiving the data... For testing, it is a simple loop (counter) with a thread delay. If I set the delay for 1 second, the textview is updated and runs smoothly. When I drop the delay to 0.1 seconds, it runs fine for a few seconds and then stutters (pauses) for 3-5 seconds. It continues this process of intermittent pausing while running. If I drop the delay to 0.01 seconds, the system crashes. My Apache server is connected to directly to my router. The Android devices are connected to my WiFi. My question is whether or not I'm doing something fundamentally wrong. I thought with memcache, I would easily be able to do 0.01 s sampling of data. Is my code properly handling the AsyncTasks? How can I prevent the Android system from apparently becoming "overloaded" with new tasks? It is as if I need a method to determine when a task is complete such that the next task can be called. I appreciate any feedback regarding php, httpclient, etc...anything that affects performance.
EDIT: My system no longer crashes when I drop the delay to 0.01 sec. I now have a catch for the null value in the onpostexecute method. However, I still get stutters/freezes.
private void startsendingdata() {
loop = 0;
if (sendingdatathread != null)
sendingdatathread.interrupt();
sendingdatathread = new Thread() {
public void run() {
while (loop < 5000) {
try {
runOnUiThread(new Runnable() {
#Ov
erride
public void run() {
new SendDataTask().execute();
loop++;
myvar = Integer.toString(loop);
}
});
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
}
};
sendingdatathread.start();
}
private class SendDataTask extends AsyncTask<String, Integer, Double> {
#Override
protected Double doInBackground(String... params) {
postData();
return null;
}
protected void onPostExecute(Double result) {
}
public void postData() {
try {
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
// put all variables here (with connection code attached)
nameValuePairs.add(new BasicNameValuePair("connectioncode",
connectioncode));
nameValuePairs.add(new BasicNameValuePair("myvar", myvar));
httppostsend
.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppostsend);
response.getEntity().consumeContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void startgettingdata() {
if (gettingdatathread != null)
gettingdatathread.interrupt();
gettingdatathread = new Thread() {
public void run() {
while (true) {
try {
runOnUiThread(new Runnable() {
#Override
public void run() {
new GetDataTask().execute();
}
});
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
}
};
gettingdatathread.start();
}
private class GetDataTask extends AsyncTask<String, Integer, Double> {
#Override
protected Double doInBackground(String... params) {
getData();
return null;
}
protected void onPostExecute(Double result) {
if (!line.isEmpty() && line!=null&&connectioncode.length() >= 6) {
tvLapTime.setText("MyVar: " + myvar);
}
}
public void getData() {
if (connectioncode.length() >= 6) {
try {
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("connectioncode",
connectioncode));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppost);
entity = response.getEntity();
is = entity.getContent();
line = convertInputStreamToString(is);
response.getEntity().consumeContent();
} catch (ClientProtocolException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
// convert inputstream to String
private static String convertInputStreamToString(InputStream inputStream)
throws IOException {
BufferedReader bufferedReader = new BufferedReader(
new InputStreamReader(inputStream));
String result = "";
while ((line = bufferedReader.readLine()) != null)
result += line;
try {
json = new JSONObject(result);
} catch (JSONException e1) {
e1.printStackTrace();
}
if (json != null) {
try {
myvar = json.getString(connectioncode + "myvar");
} catch (JSONException e) {
e.printStackTrace();
}
}
inputStream.close();
return result;
}

Do away with startsendingdata() and startgettingdata(). In the onPostExecute() of the tasks initiate the start of the next task. Now you are sure a task is finished before starting a new one. For instance you could start a timer which executes the next task.

How restart bluetooth service in bluecove?

I have desktop and android applications, which connected by bluetooth(in desktop side I use Bluecove 2.1.1 library). Desktop application create bluetooth service then android application connects to it. I want to add logout functionality from both desktop and android sides. For example in desktop app user click disconnect, both desktop and android apps reset their connections and should be able to connect again. Here is bluetoothService code for desktop side:
public class BluetoothService
{
private static final String serviceName = "btspp://localhost:"
// + new UUID("0000110100001000800000805F9B34F7", false).toString()
// + new UUID("0000110100001000800000805F9B34F8", false).toString()
+ new UUID("0000110100001000800000805F9B34F9", false).toString()
+ ";name=serviceName";
private StreamConnectionNotifier m_service = null;
private ListenerThread m_listenerThread;
private DataOutputStream m_outStream;
public BluetoothService()
{
Open();
}
public void Open()
{
try
{
assert (m_service == null);
m_service = (StreamConnectionNotifier) Connector.open(serviceName);
}
catch (IOException e)
{
e.printStackTrace();
}
}
public void Start()
{
try
{
StreamConnection connection = (StreamConnection) m_service
.acceptAndOpen();
System.out.println("Connected");
m_listenerThread = new ListenerThread(connection);
Thread listener = new Thread(m_listenerThread);
listener.start();
m_outStream = new DataOutputStream(connection.openOutputStream());
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void Send(String message)
{
assert (m_listenerThread != null);
try
{
m_outStream.writeUTF(message);
m_outStream.flush();
System.out.println("Sent: " + message);
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void Close()
{
try
{
m_service.close();
m_listenerThread.Stop();
m_listenerThread = null;
m_outStream.close();
m_outStream = null;
m_service = null;
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
class ListenerThread implements Runnable
{
private DataInputStream m_inStream;
private boolean m_isRunning;
public ListenerThread(StreamConnection connection)
{
try
{
this.m_inStream = new DataInputStream(connection.openInputStream());
m_isRunning = true;
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
;
}
public void run()
{
while (m_isRunning)
{
try
{
assert (m_inStream != null);
if (m_inStream.available() > 0)
{
String message = m_inStream.readUTF();
System.out.println("Received command: " + message);
CommandManager.getInstance().Parse(message);
}
}
catch (IOException e)
{
System.err.println(e.toString());
}
}
}
public void Stop()
{
m_isRunning = false;
try
{
m_inStream.close();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
for restarting service I do:
BluetoothService::Close();
BluetoothService::Open();
BluetoothService::Start();
but seems I cannot reconnect. Maybe I should create service with different name?

Android Http API

I am trying to write a Http API in android. I am using a AsyncTask to run the calls to my web service.I am not interested in updating the UI, instead all I want is the data to use in my application logic. This is what I have so far:
public class DataManager{
public static String result;
public DataManager ()
{
}
public String get ()
{
User user = new User ();
user.execute("http://someuri/service/users/id/21001");
return user.getResult();
}
}
public class User extends AsyncTask <String,Void,String>{
private String result;
#Override
protected String doInBackground(String... arg0)
{
HttpClient client = new DefaultHttpClient();
HttpGet get = new HttpGet (arg0[0]);
try
{
HttpResponse response = client.execute (get);
if (response.getStatusLine().getStatusCode () == 200)
{
HttpEntity entity = response.getEntity();
return EntityUtils.toString(entity);
}
}
catch (ClientProtocolException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
this.result = result;
}
public String getResult ()
{
return result;
}
}
I want a typical call to be:
DataManager manager = new DataManager ();
String value = manager.get ();
But when I run this I get back null. What is causing this and how can I refactor this code to get the desired behavior.

The whole idea of a thread is that it runs concurrently. Basically, here's what you're doing:
User user = new User (); // Create User object
user.execute("http://someuri/service/users/id/21001"); // Start thread
return user.getResult(); // Return thread result
However, there is no time for the thread to run between "start" and "return result".
I would suggest using some kind of callback; first, make get() return void, and remove the return statement. Then, you pass in some object which implements YourCallback, and then call onCallback(result) from within onPostExecute().
Your calling code would then look like this:
DataManager x = new DataManager();
x.get(new YourCallback() {
public void onCallback(String result) {
// ...
}
});
There is a much fuller example in this fantastic answer.