HttpGet funktioniert nicht

<---package--->

<---imports--->

public class MainActivity extends ActionBarActivity {
	private EditText pass;
	private Button einloggen;
	private EditText user;
	private TextView debuggingOutput;
	String username, passwort, hash, result;
	HttpConnect http;
	
	
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // Variablenzuweisung des Layouts
        pass = (EditText) findViewById(R.id.passwort);
        einloggen = (Button) findViewById(R.id.bt_einloggen);
        user = (EditText) findViewById(R.id.username);
        
        // Debug
        debuggingOutput = (TextView) findViewById(R.id.debuggingOutput);
      
        einloggen.setOnClickListener(new View.OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
            	hole_daten();
            	if (!passwort.contentEquals("") & !username.contentEquals("")) {
            		
            		try { hash = generiereHash(passwort); }          			
            		// Fehler bei der Hash Generierung abfangen	:
            		catch (NoSuchAlgorithmException e) {e.printStackTrace();}						
					catch (UnsupportedEncodingException e) {e.printStackTrace();}
					
    				http = new HttpConnect("http://my-server-url/http_get.php?user="+username+"&hash="+hash);
    				try {http.sendGet();} 
    				catch (Exception e) {e.printStackTrace();}
    				result = http.getResult();
    				
    				
    				
    				dbg("RESULT:"+result);
    				
    				
            		
        			if(result.equals("false")) Toast.makeText(getApplicationContext(), R.string.wrongPassword, Toast.LENGTH_LONG).show();    			
        			else {
        				Toast.makeText(getApplicationContext(), "PW korrekt", Toast.LENGTH_LONG).show();
        				//TODO: OPEN NEW ACTIVITY!
        			}
        			
              	}
            	// Leere Eingaben abfangen
            	else if(passwort.contentEquals("") & username.contentEquals("")) Toast.makeText(getApplicationContext(), R.string.invalidInput, Toast.LENGTH_LONG).show();
            	else if(passwort.contentEquals("") & !username.contentEquals("")) Toast.makeText(getApplicationContext(), R.string.invalidInputNoPassword, Toast.LENGTH_LONG).show();
            	else if(!passwort.contentEquals("") & username.contentEquals("")) Toast.makeText(getApplicationContext(), R.string.invalidInputNoUsername, Toast.LENGTH_LONG).show();
            	}
          });
    }
    public String generiereHash(String passwort) throws NoSuchAlgorithmException, UnsupportedEncodingException{
        
          <.....>
       
     }
     
     private static String convertToHex(byte[] data)
     {
           <.....>
     }

    public void hole_daten(){
        username = user.getText().toString();
        passwort = pass.getText().toString();
      }    

    public void dbg(String s){
    	debuggingOutput.setText(debuggingOutput.getText().toString() + "\n" + s);
    }
    
    public void dbg(String s, boolean clear){
    	debuggingOutput.setText("DEBUG OUT: \n" + s);
    }  
    
    
    
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
<.....>
 }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
<.....>
    }
}

<-- package -->

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpConnect {
	
	private final String USER_AGENT = "Mozilla/5.0";
	public String url;
	public String result;
	
	public HttpConnect(String Url){
		url = Url;
		result = "";
	}
	
	public String getResult(){
		return result;
	}
	 
	// HTTP GET request
	public void sendGet() throws Exception {				 
		URL obj = new URL(url);
		HttpURLConnection con = (HttpURLConnection) obj.openConnection();
 
		con.setRequestMethod("GET");
 
		con.setRequestProperty("User-Agent", USER_AGENT);
 
		BufferedReader in = new BufferedReader(
		        new InputStreamReader(con.getInputStream()));
		String inputLine;
		StringBuffer response = new StringBuffer();
 
		while ((inputLine = in.readLine()) != null) {
			response.append(inputLine);
		}
		in.close();
 
		result = response.toString(); 
	}	
}

<?php			 
$db = mysqli_connect("**","**","**","**");
if(!$db){
	exit("Verbindungsfehler: ".mysqli_connect_error());
}

$user     = urldecode($_GET['user']);
$hash    = urldecode($_GET['hash']);

$query = "SELECT * FROM test WHERE user='".$user."'";

$get = mysqli_query($db, $query);

while($row = mysqli_fetch_object($get))
{
	$validHash = $row->password;
}

if($hash == $validHash) $valid="true";
else $valid="false";

print $valid; 
 
?>