问使用文件的URL检查远程服务器上是否存在该文件

EN

public static boolean exists(String URLName){
    try {
      HttpURLConnection.setFollowRedirects(false);
      // note : you may also need
      //        HttpURLConnection.setInstanceFollowRedirects(false)
      HttpURLConnection con =
         (HttpURLConnection) new URL(URLName).openConnection();
      con.setRequestMethod("HEAD");
      return (con.getResponseCode() == HttpURLConnection.HTTP_OK);
    }
    catch (Exception e) {
       e.printStackTrace();
       return false;
    }
  }  

public class MainActivity extends Activity {

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

    String customURL = "http://www.desicomments.com/dc3/08/273858/273858.jpg";

    MyTask task = new MyTask();
    task.execute(customURL);
}


private class MyTask extends AsyncTask<String, Void, Boolean> {

    @Override
    protected void onPreExecute() {

    }

    @Override
    protected Boolean doInBackground(String... params) {

         try {
                HttpURLConnection.setFollowRedirects(false);
                HttpURLConnection con =  (HttpURLConnection) new URL(params[0]).openConnection();
                con.setRequestMethod("HEAD");
                System.out.println(con.getResponseCode()); 
                return (con.getResponseCode() == HttpURLConnection.HTTP_OK);
            }
            catch (Exception e) {   
                e.printStackTrace();    
                return false;
            }
    }

    @Override
    protected void onPostExecute(Boolean result) {
        boolean bResponse = result;
         if (bResponse==true)
            {
                Toast.makeText(MainActivity.this, "File exists!", Toast.LENGTH_SHORT).show();      
            }
            else
            {           
                Toast.makeText(MainActivity.this, "File does not exist!", Toast.LENGTH_SHORT).show();
            }                  
    }           
}
}