Android - How to download a file from a webserver

Question

In my app I am downloading a kml file from a webserver. I have set the permission for external storage and internet in my android manifest file. I am new to Android, your help is greatly appreciated.

MainActivity.java

package com.example.demo;  import java.io.DataInputStream; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.net.MalformedURLException; import java.net.URL;  import android.app.Activity; import android.os.Bundle; import android.os.Environment; import android.util.Log; import android.view.Menu;  public class MainActivity extends Activity {      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          DownloadFiles();     }      public void DownloadFiles(){         try {             URL u = new URL("http://www.qwikisoft.com/demo/ashade/20001.kml");             InputStream is = u.openStream();             DataInputStream dis = new DataInputStream(is);              byte[] buffer = new byte[1024];             int length;              FileOutputStream fos = new FileOutputStream(new File(Environment.getExternalStorageDirectory() + "/" + "data/test.kml"));             while ((length = dis.read(buffer)) > 0) {                 fos.write(buffer, 0, length);             }          } catch (MalformedURLException mue) {             Log.e("SYNC getUpdate", "malformed url error", mue);         } catch (IOException ioe) {             Log.e("SYNC getUpdate", "io error", ioe);         } catch (SecurityException se) {             Log.e("SYNC getUpdate", "security error", se);         }     } } 

Android Manifest File

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.example.demo"     android:versionCode="1"     android:versionName="1.0" >      <uses-sdk         android:minSdkVersion="8"         android:targetSdkVersion="16" />     <uses-permission android:name="android.permission.INTERNET"/>     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>      <application         android:allowBackup="true"         android:icon="@drawable/ic_launcher"         android:label="@string/app_name"         android:theme="@style/AppTheme" >          <activity             android:name="com.example.demo.MainActivity"             android:label="@string/app_name" >             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                  <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>     </application> </manifest> 

Logcat error:

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.demo/com.example.demo.MainActivity}: android.os.NetworkOnMainThreadException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) at android.app.ActivityThread.access$600(ActivityThread.java:123) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4424) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) at dalvik.system.NativeStart.main(Native Method) Caused by: android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099) at java.net.InetAddress.lookupHostByName(InetAddress.java:391) at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242) at java.net.InetAddress.getAllByName(InetAddress.java:220) at libcore.net.http.HttpConnection.(HttpConnection.java:71) at libcore.net.http.HttpConnection.(HttpConnection.java:50) at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351) at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86) at libcore.net.http.HttpConnection.connect(HttpConnection.java:128) at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308) at libcore.net.http.HttpEngine.connect(HttpEngine.java:303) at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282) at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232) at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273) at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168) at java.net.URL.openStream(URL.java:462) at com.example.demo.MainActivity.DownloadFiles(MainActivity.java:30) at com.example.demo.MainActivity.onCreate(MainActivity.java:24) at android.app.Activity.performCreate(Activity.java:4465) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

EDIT

package com.example.demo;  import java.io.BufferedInputStream; import java.io.FileOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.net.URL; import java.net.URLConnection;  import android.app.Activity; import android.app.Dialog; import android.app.ProgressDialog; import android.os.AsyncTask; import android.os.Bundle; import android.os.Environment; import android.util.Log;  public class MainActivity extends Activity {      private ProgressDialog pDialog;     public static final int progress_bar_type = 0;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          new DownloadFileFromURL().execute("http://www.qwikisoft.com/demo/ashade/20001.kml");     }      @Override     protected Dialog onCreateDialog(int id) {         switch (id) {             case progress_bar_type: // we set this to 0                 pDialog = new ProgressDialog(this);                 pDialog.setMessage("Downloading file. Please wait...");                 pDialog.setIndeterminate(false);                 pDialog.setMax(100);                 pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);                 pDialog.setCancelable(true);                 pDialog.show();                 return pDialog;             default:                 return null;         }     }      class DownloadFileFromURL extends AsyncTask<String, String, String> {          /**          * Before starting background thread Show Progress Bar Dialog          **/         @Override         protected void onPreExecute() {             super.onPreExecute();             showDialog(progress_bar_type);         }          /**          * Downloading file in background thread          **/         @Override         protected String doInBackground(String... f_url) {             int count;             try {                 URL url = new URL(f_url[0]);                 URLConnection conection = url.openConnection();                 conection.connect();                  // this will be useful so that you can show a tipical 0-100%                 // progress bar                 int lenghtOfFile = conection.getContentLength();                  // download the file                 InputStream input = new BufferedInputStream(url.openStream(),                         8192);                  // Output stream                 OutputStream output = new FileOutputStream(Environment                         .getExternalStorageDirectory().toString()                         + "/data/downloadedfile.kml");                  byte data[] = new byte[1024];                  long total = 0;                  while ((count = input.read(data)) != -1) {                     total += count;                     // publishing the progress....                     // After this onProgressUpdate will be called                     publishProgress("" + (int) ((total * 100) / lenghtOfFile));                      // writing data to file                     output.write(data, 0, count);                 }                  // flushing output                 output.flush();                  // closing streams                 output.close();                 input.close();             } catch (Exception e) {                 Log.e("Error: ", e.getMessage());             }              return null;         }          /**          * Updating progress bar          **/         protected void onProgressUpdate(String... progress) {             // setting progress percentage             pDialog.setProgress(Integer.parseInt(progress[0]));         }          /**          * After completing background task Dismiss the progress dialog          **/         @Override         protected void onPostExecute(String file_url) {             // dismiss the dialog after the file was downloaded             dismissDialog(progress_bar_type);         }     } } 

When I run this code in the emulator the code still does not work - the file is not getting downloaded.

Answer 1

Using Async task

call when you want to download file : new DownloadFileFromURL().execute(file_url);

public class MainActivity extends Activity {      // Progress Dialog     private ProgressDialog pDialog;     public static final int progress_bar_type = 0;      // File url to download     private static String file_url = "http://www.qwikisoft.com/demo/ashade/20001.kml";      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);          setContentView(R.layout.activity_main);          new DownloadFileFromURL().execute(file_url);      }      /**      * Showing Dialog      * */      @Override     protected Dialog onCreateDialog(int id) {         switch (id) {         case progress_bar_type: // we set this to 0             pDialog = new ProgressDialog(this);             pDialog.setMessage("Downloading file. Please wait...");             pDialog.setIndeterminate(false);             pDialog.setMax(100);             pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);             pDialog.setCancelable(true);             pDialog.show();             return pDialog;         default:             return null;         }     }      /**      * Background Async Task to download file      * */     class DownloadFileFromURL extends AsyncTask<String, String, String> {          /**          * Before starting background thread Show Progress Bar Dialog          * */         @Override         protected void onPreExecute() {             super.onPreExecute();             showDialog(progress_bar_type);         }          /**          * Downloading file in background thread          * */         @Override         protected String doInBackground(String... f_url) {             int count;             try {                 URL url = new URL(f_url[0]);                 URLConnection connection = url.openConnection();                 connection.connect();                  // this will be useful so that you can show a tipical 0-100%                 // progress bar                 int lenghtOfFile = connection.getContentLength();                  // download the file                 InputStream input = new BufferedInputStream(url.openStream(),                         8192);                  // Output stream                 OutputStream output = new FileOutputStream(Environment                         .getExternalStorageDirectory().toString()                         + "/2011.kml");                  byte data[] = new byte[1024];                  long total = 0;                  while ((count = input.read(data)) != -1) {                     total += count;                     // publishing the progress....                     // After this onProgressUpdate will be called                     publishProgress("" + (int) ((total * 100) / lenghtOfFile));                      // writing data to file                     output.write(data, 0, count);                 }                  // flushing output                 output.flush();                  // closing streams                 output.close();                 input.close();              } catch (Exception e) {                 Log.e("Error: ", e.getMessage());             }              return null;         }          /**          * Updating progress bar          * */         protected void onProgressUpdate(String... progress) {             // setting progress percentage             pDialog.setProgress(Integer.parseInt(progress[0]));         }          /**          * After completing background task Dismiss the progress dialog          * **/         @Override         protected void onPostExecute(String file_url) {             // dismiss the dialog after the file was downloaded             dismissDialog(progress_bar_type);          }      } } 

if not working in 4.0 then add:

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); StrictMode.setThreadPolicy(policy);  

Answer 2

Simple kotlin version

fun download(link: String, path: String) {     URL(link).openStream().use { input ->         FileOutputStream(File(path)).use { output ->             input.copyTo(output)         }     } } 

is there anyway to get the download progress or downloaded size from this method ?

This is the same realization as defined in InputStream.copyTo, but with progress

/*inline*/ fun download(link: String, path: String, progress: ((Long, Long) -> Unit)? = null): Long {     val url = URL(link)     val connection = url.openConnection()     connection.connect()     val length = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) connection.contentLengthLong else         connection.contentLength.toLong()     url.openStream().use { input ->         FileOutputStream(File(path)).use { output ->             val buffer = ByteArray(DEFAULT_BUFFER_SIZE)             var bytesRead = input.read(buffer)             var bytesCopied = 0L             while (bytesRead >= 0) {                 output.write(buffer, 0, bytesRead)                 bytesCopied += bytesRead                 progress?.invoke(bytesCopied, length)                 bytesRead = input.read(buffer)             }             return bytesCopied         }     } } 

An example of usage:

val handler = object : Handler(Looper.getMainLooper()) {      override fun handleMessage(msg: Message) {         // length may be negative because it is based on http header         val (progress, length) = msg.obj as Pair<Long, Long>     } }  // call this outside of main thread val totalSize = download("http://example.site/path/to/file", "path/to/file") { progress, length ->     // handling the result on main thread     handler.sendMessage(handler.obtainMessage(0, progress to length)) }