问题
How do you download and save an image from a given url in Android?
回答1:
Edit as of 30.12.2015 - The Ultimate Guide to image downloading
last major update: Mar 31 2016
TL;DR a.k.a. stop talking, just give me the code!!
Skip to the bottom of this post, copy the
BasicImageDownloader(javadoc version here) into your project, implement theOnImageLoaderListenerinterface and you're done.Note: though the
BasicImageDownloaderhandles possible errors and will prevent your app from crashing in case anything goes wrong, it will not perform any post-processing (e.g. downsizing) on the downloadedBitmaps.
Since this post has received quite a lot of attention, I have decided to completely rework it to prevent the folks from using deprecated technologies, bad programming practices or just doing silly things - like looking for "hacks" to run network on the main thread or accept all SSL certs.
I've created a demo project named "Image Downloader" that demonstrates how to download (and save) an image using my own downloader implementation, the Android's built-in DownloadManager as well as some popular open-source libraries. You can view the complete source code or download the project on GitHub.
Note: I have not adjusted the permission management for SDK 23+ (Marshmallow) yet, thus the project is targeting SDK 22 (Lollipop).
In my conclusion at the end of this post I will share my humble opinion about the proper use-case for each particular way of image downloading I've mentioned.
Let's start with an own implementation (you can find the code at the end of the post). First of all, this is a BasicImageDownloader and that's it. All it does is connecting to the given url, reading the data and trying to decode it as a Bitmap, triggering the OnImageLoaderListener interface callbacks when appropriate.
The advantage of this approach - it is simple and you have a clear overview of what's going on. A good way to go if all you need is downloading/displaying and saving some images, whilst you don't care about maintaining a memory/disk cache.
Note: in case of large images, you might need to scale them down.
--
Android DownloadManager is a way to let the system handle the download for you. It's actually capable of downloading any kind of files, not just images. You may let your download happen silently and invisible to the user, or you can enable the user to see the download in the notification area. You can also register a BroadcastReceiver to get notified after you download is complete. The setup is pretty much straightforward, refer to the linked project for sample code.
Using the DownloadManager is generally not a good idea if you also want to display the image, since you'd need to read and decode the saved file instead of just setting the downloaded Bitmap into an ImageView. The DownloadManager also does not provide any API for you app to track the download progress.
--
Now the introduction of the great stuff - the libraries. They can do much more than just downloading and displaying images, including: creating and managing the memory/disk cache, resizing images, transforming them and more.
I will start with Volley, a powerful library created by Google and covered by the official documentation. While being a general-purpose networking library not specializing on images, Volley features quite a powerful API for managing images.
You will need to implement a Singleton class for managing Volley requests and you are good to go.
You might want to replace your ImageView with Volley's NetworkImageView, so the download basically becomes a one-liner:
((NetworkImageView) findViewById(R.id.myNIV)).setImageUrl(url, MySingleton.getInstance(this).getImageLoader());
If you need more control, this is what it looks like to create an ImageRequest with Volley:
ImageRequest imgRequest = new ImageRequest(url, new Response.Listener<Bitmap>() {
@Override
public void onResponse(Bitmap response) {
//do stuff
}
}, 0, 0, ImageView.ScaleType.CENTER_CROP, Bitmap.Config.ARGB_8888,
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
//do stuff
}
});
It is worth mentioning that Volley features an excellent error handling mechanism by providing the VolleyError class that helps you to determine the exact cause of an error. If your app does a lot of networking and managing images isn't its main purpose, then Volley it a perfect fit for you.
--
Square's Picasso is a well-known library which will do all of the image loading stuff for you. Just displaying an image using Picasso is as simple as:
Picasso.with(myContext)
.load(url)
.into(myImageView);
By default, Picasso manages the disk/memory cache so you don't need to worry about that. For more control you can implement the Target interface and use it to load your image into - this will provide callbacks similar to the Volley example. Check the demo project for examples.
Picasso also lets you apply transformations to the downloaded image and there are even other libraries around that extend those API. Also works very well in a RecyclerView/ListView/GridView.
--
Universal Image Loader is an another very popular library serving the purpose of image management. It uses its own ImageLoader that (once initialized) has a global instance which can be used to download images in a single line of code:
ImageLoader.getInstance().displayImage(url, myImageView);
If you want to track the download progress or access the downloaded Bitmap:
ImageLoader.getInstance().displayImage(url, myImageView, opts,
new ImageLoadingListener() {
@Override
public void onLoadingStarted(String imageUri, View view) {
//do stuff
}
@Override
public void onLoadingFailed(String imageUri, View view, FailReason failReason) {
//do stuff
}
@Override
public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
//do stuff
}
@Override
public void onLoadingCancelled(String imageUri, View view) {
//do stuff
}
}, new ImageLoadingProgressListener() {
@Override
public void onProgressUpdate(String imageUri, View view, int current, int total) {
//do stuff
}
});
The opts argument in this example is a DisplayImageOptions object. Refer to the demo project to learn more.
Similar to Volley, UIL provides the FailReason class that enables you to check what went wrong on download failure. By default, UIL maintains a memory/disk cache if you don't explicitly tell it not to do so.
Note: the author has mentioned that he is no longer maintaining the project as of Nov 27th, 2015. But since there are many contributors, we can hope that the Universal Image Loader will live on.
--
Facebook's Fresco is the newest and (IMO) the most advanced library that takes image management to a new level: from keeping Bitmaps off the java heap (prior to Lollipop) to supporting animated formats and progressive JPEG streaming.
To learn more about ideas and techniques behind Fresco, refer to this post.
The basic usage is quite simple. Note that you'll need to call Fresco.initialize(Context); only once, preferable in the Application class. Initializing Fresco more than once may lead to unpredictable behavior and OOM errors.
Fresco uses Drawees to display images, you can think of them as of ImageViews:
<com.facebook.drawee.view.SimpleDraweeView
android:id="@+id/drawee"
android:layout_width="match_parent"
android:layout_height="match_parent"
fresco:fadeDuration="500"
fresco:actualImageScaleType="centerCrop"
fresco:placeholderImage="@drawable/placeholder_grey"
fresco:failureImage="@drawable/error_orange"
fresco:placeholderImageScaleType="fitCenter"
fresco:failureImageScaleType="centerInside"
fresco:retryImageScaleType="centerCrop"
fresco:progressBarImageScaleType="centerInside"
fresco:progressBarAutoRotateInterval="1000"
fresco:roundAsCircle="false" />
As you can see, a lot of stuff (including transformation options) gets already defined in XML, so all you need to do to display an image is a one-liner:
mDrawee.setImageURI(Uri.parse(url));
Fresco provides an extended customization API, which, under circumstances, can be quite complex and requires the user to read the docs carefully (yes, sometimes you need to RTFM).
I have included examples for progressive JPEG's and animated images into the sample project.
Conclusion - "I have learned about the great stuff, what should I use now?"
Note that the following text reflects my personal opinion and should not be taken as a postulate.
- If you only need to download/save/display some images, don't plan to use them in a
Recycler-/Grid-/ListViewand don't need a whole bunch of images to be display-ready, the BasicImageDownloader should fit your needs. - If your app saves images (or other files) as a result of a user or an automated action and you don't need the images to be displayed often, use the Android DownloadManager.
- In case your app does a lot of networking, transmits/receives
JSONdata, works with images, but those are not the main purpose of the app, go with Volley. - Your app is image/media-focused, you'd like to apply some transformations to images and don't want to bother with complex API: use Picasso (Note: does not provide any API to track the intermediate download status) or Universal Image Loader
- If your app is all about images, you need advanced features like displaying animated formats and you are ready to read the docs, go with Fresco.
In case you missed that, the Github link for the demo project.
And here's the BasicImageDownloader.java
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.support.annotation.NonNull;
import android.util.Log;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.HashSet;
import java.util.Set;
public class BasicImageDownloader {
private OnImageLoaderListener mImageLoaderListener;
private Set<String> mUrlsInProgress = new HashSet<>();
private final String TAG = this.getClass().getSimpleName();
public BasicImageDownloader(@NonNull OnImageLoaderListener listener) {
this.mImageLoaderListener = listener;
}
public interface OnImageLoaderListener {
void onError(ImageError error);
void onProgressChange(int percent);
void onComplete(Bitmap result);
}
public void download(@NonNull final String imageUrl, final boolean displayProgress) {
if (mUrlsInProgress.contains(imageUrl)) {
Log.w(TAG, "a download for this url is already running, " +
"no further download will be started");
return;
}
new AsyncTask<Void, Integer, Bitmap>() {
private ImageError error;
@Override
protected void onPreExecute() {
mUrlsInProgress.add(imageUrl);
Log.d(TAG, "starting download");
}
@Override
protected void onCancelled() {
mUrlsInProgress.remove(imageUrl);
mImageLoaderListener.onError(error);
}
@Override
protected void onProgressUpdate(Integer... values) {
mImageLoaderListener.onProgressChange(values[0]);
}
@Override
protected Bitmap doInBackground(Void... params) {
Bitmap bitmap = null;
HttpURLConnection connection = null;
InputStream is = null;
ByteArrayOutputStream out = null;
try {
connection = (HttpURLConnection) new URL(imageUrl).openConnection();
if (displayProgress) {
connection.connect();
final int length = connection.getContentLength();
if (length <= 0) {
error = new ImageError("Invalid content length. The URL is probably not pointing to a file")
.setErrorCode(ImageError.ERROR_INVALID_FILE);
this.cancel(true);
}
is = new BufferedInputStream(connection.getInputStream(), 8192);
out = new ByteArrayOutputStream();
byte bytes[] = new byte[8192];
int count;
long read = 0;
while ((count = is.read(bytes)) != -1) {
read += count;
out.write(bytes, 0, count);
publishProgress((int) ((read * 100) / length));
}
bitmap = BitmapFactory.decodeByteArray(out.toByteArray(), 0, out.size());
} else {
is = connection.getInputStream();
bitmap = BitmapFactory.decodeStream(is);
}
} catch (Throwable e) {
if (!this.isCancelled()) {
error = new ImageError(e).setErrorCode(ImageError.ERROR_GENERAL_EXCEPTION);
this.cancel(true);
}
} finally {
try {
if (connection != null)
connection.disconnect();
if (out != null) {
out.flush();
out.close();
}
if (is != null)
is.close();
} catch (Exception e) {
e.printStackTrace();
}
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap result) {
if (result == null) {
Log.e(TAG, "factory returned a null result");
mImageLoaderListener.onError(new ImageError("downloaded file could not be decoded as bitmap")
.setErrorCode(ImageError.ERROR_DECODE_FAILED));
} else {
Log.d(TAG, "download complete, " + result.getByteCount() +
" bytes transferred");
mImageLoaderListener.onComplete(result);
}
mUrlsInProgress.remove(imageUrl);
System.gc();
}
}.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
public interface OnBitmapSaveListener {
void onBitmapSaved();
void onBitmapSaveError(ImageError error);
}
public static void writeToDisk(@NonNull final File imageFile, @NonNull final Bitmap image,
@NonNull final OnBitmapSaveListener listener,
@NonNull final Bitmap.CompressFormat format, boolean shouldOverwrite) {
if (imageFile.isDirectory()) {
listener.onBitmapSaveError(new ImageError("the specified path points to a directory, " +
"should be a file").setErrorCode(ImageError.ERROR_IS_DIRECTORY));
return;
}
if (imageFile.exists()) {
if (!shouldOverwrite) {
listener.onBitmapSaveError(new ImageError("file already exists, " +
"write operation cancelled").setErrorCode(ImageError.ERROR_FILE_EXISTS));
return;
} else if (!imageFile.delete()) {
listener.onBitmapSaveError(new ImageError("could not delete existing file, " +
"most likely the write permission was denied")
.setErrorCode(ImageError.ERROR_PERMISSION_DENIED));
return;
}
}
File parent = imageFile.getParentFile();
if (!parent.exists() && !parent.mkdirs()) {
listener.onBitmapSaveError(new ImageError("could not create parent directory")
.setErrorCode(ImageError.ERROR_PERMISSION_DENIED));
return;
}
try {
if (!imageFile.createNewFile()) {
listener.onBitmapSaveError(new ImageError("could not create file")
.setErrorCode(ImageError.ERROR_PERMISSION_DENIED));
return;
}
} catch (IOException e) {
listener.onBitmapSaveError(new ImageError(e).setErrorCode(ImageError.ERROR_GENERAL_EXCEPTION));
return;
}
new AsyncTask<Void, Void, Void>() {
private ImageError error;
@Override
protected Void doInBackground(Void... params) {
FileOutputStream fos = null;
try {
fos = new FileOutputStream(imageFile);
image.compress(format, 100, fos);
} catch (IOException e) {
error = new ImageError(e).setErrorCode(ImageError.ERROR_GENERAL_EXCEPTION);
this.cancel(true);
} finally {
if (fos != null) {
try {
fos.flush();
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return null;
}
@Override
protected void onCancelled() {
listener.onBitmapSaveError(error);
}
@Override
protected void onPostExecute(Void result) {
listener.onBitmapSaved();
}
}.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
public static Bitmap readFromDisk(@NonNull File imageFile) {
if (!imageFile.exists() || imageFile.isDirectory()) return null;
return BitmapFactory.decodeFile(imageFile.getAbsolutePath());
}
public interface OnImageReadListener {
void onImageRead(Bitmap bitmap);
void onReadFailed();
}
public static void readFromDiskAsync(@NonNull File imageFile, @NonNull final OnImageReadListener listener) {
new AsyncTask<String, Void, Bitmap>() {
@Override
protected Bitmap doInBackground(String... params) {
return BitmapFactory.decodeFile(params[0]);
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if (bitmap != null)
listener.onImageRead(bitmap);
else
listener.onReadFailed();
}
}.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, imageFile.getAbsolutePath());
}
public static final class ImageError extends Throwable {
private int errorCode;
public static final int ERROR_GENERAL_EXCEPTION = -1;
public static final int ERROR_INVALID_FILE = 0;
public static final int ERROR_DECODE_FAILED = 1;
public static final int ERROR_FILE_EXISTS = 2;
public static final int ERROR_PERMISSION_DENIED = 3;
public static final int ERROR_IS_DIRECTORY = 4;
public ImageError(@NonNull String message) {
super(message);
}
public ImageError(@NonNull Throwable error) {
super(error.getMessage(), error.getCause());
this.setStackTrace(error.getStackTrace());
}
public ImageError setErrorCode(int code) {
this.errorCode = code;
return this;
}
public int getErrorCode() {
return errorCode;
}
}
}
回答2:
I have just came from solving this problem on and I would like to share the complete code that can download, save to the sdcard (and hide the filename) and retrieve the images and finally it checks if the image is already there. The url comes from the database so the filename can be uniquely easily using id.
first download images
private class GetImages extends AsyncTask<Object, Object, Object> {
private String requestUrl, imagename_;
private ImageView view;
private Bitmap bitmap ;
private FileOutputStream fos;
private GetImages(String requestUrl, ImageView view, String _imagename_) {
this.requestUrl = requestUrl;
this.view = view;
this.imagename_ = _imagename_ ;
}
@Override
protected Object doInBackground(Object... objects) {
try {
URL url = new URL(requestUrl);
URLConnection conn = url.openConnection();
bitmap = BitmapFactory.decodeStream(conn.getInputStream());
} catch (Exception ex) {
}
return null;
}
@Override
protected void onPostExecute(Object o) {
if(!ImageStorage.checkifImageExists(imagename_))
{
view.setImageBitmap(bitmap);
ImageStorage.saveToSdCard(bitmap, imagename_);
}
}
}
Then create a class for saving and retrieving the files
public class ImageStorage {
public static String saveToSdCard(Bitmap bitmap, String filename) {
String stored = null;
File sdcard = Environment.getExternalStorageDirectory() ;
File folder = new File(sdcard.getAbsoluteFile(), ".your_specific_directory");//the dot makes this directory hidden to the user
folder.mkdir();
File file = new File(folder.getAbsoluteFile(), filename + ".jpg") ;
if (file.exists())
return stored ;
try {
FileOutputStream out = new FileOutputStream(file);
bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
out.flush();
out.close();
stored = "success";
} catch (Exception e) {
e.printStackTrace();
}
return stored;
}
public static File getImage(String imagename) {
File mediaImage = null;
try {
String root = Environment.getExternalStorageDirectory().toString();
File myDir = new File(root);
if (!myDir.exists())
return null;
mediaImage = new File(myDir.getPath() + "/.your_specific_directory/"+imagename);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return mediaImage;
}
public static boolean checkifImageExists(String imagename)
{
Bitmap b = null ;
File file = ImageStorage.getImage("/"+imagename+".jpg");
String path = file.getAbsolutePath();
if (path != null)
b = BitmapFactory.decodeFile(path);
if(b == null || b.equals(""))
{
return false ;
}
return true ;
}
}
Then To access the images first check if it is already there if not then download
if(ImageStorage.checkifImageExists(imagename))
{
File file = ImageStorage.getImage("/"+imagename+".jpg");
String path = file.getAbsolutePath();
if (path != null){
b = BitmapFactory.decodeFile(path);
imageView.setImageBitmap(b);
}
} else {
new GetImages(imgurl, imageView, imagename).execute() ;
}
回答3:
Why do you really need your own code to download it? How about just passing your URI to Download manager?
public void downloadFile(String uRl) {
File direct = new File(Environment.getExternalStorageDirectory()
+ "/AnhsirkDasarp");
if (!direct.exists()) {
direct.mkdirs();
}
DownloadManager mgr = (DownloadManager) getActivity().getSystemService(Context.DOWNLOAD_SERVICE);
Uri downloadUri = Uri.parse(uRl);
DownloadManager.Request request = new DownloadManager.Request(
downloadUri);
request.setAllowedNetworkTypes(
DownloadManager.Request.NETWORK_WIFI
| DownloadManager.Request.NETWORK_MOBILE)
.setAllowedOverRoaming(false).setTitle("Demo")
.setDescription("Something useful. No, really.")
.setDestinationInExternalPublicDir("/AnhsirkDasarp", "fileName.jpg");
mgr.enqueue(request);
}
回答4:
it might help you..
Button download_image = (Button)bigimagedialog.findViewById(R.id.btn_downloadimage);
download_image.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
boolean success = (new File("/sdcard/dirname")).mkdir();
if (!success)
{
Log.w("directory not created", "directory not created");
}
try
{
URL url = new URL("YOUR_URL");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(input);
String data1 = String.valueOf(String.format("/sdcard/dirname/%d.jpg",System.currentTimeMillis()));
FileOutputStream stream = new FileOutputStream(data1);
ByteArrayOutputStream outstream = new ByteArrayOutputStream();
myBitmap.compress(Bitmap.CompressFormat.JPEG, 85, outstream);
byte[] byteArray = outstream.toByteArray();
stream.write(byteArray);
stream.close();
Toast.makeText(getApplicationContext(), "Downloading Completed", Toast.LENGTH_SHORT).show();
}
catch (Exception e)
{
e.printStackTrace();
}
}
});
回答5:
I have a simple solution which is working perfectly. The code is not mine, I found it on this link. Here are the steps to follow:
1. Before downloading the image, let’s write a method for saving bitmap into an image file in the internal storage in android. It needs a context, better to use the pass in the application context by getApplicationContext(). This method can be dumped into your Activity class or other util classes.
public void saveImage(Context context, Bitmap b, String imageName)
{
FileOutputStream foStream;
try
{
foStream = context.openFileOutput(imageName, Context.MODE_PRIVATE);
b.compress(Bitmap.CompressFormat.PNG, 100, foStream);
foStream.close();
}
catch (Exception e)
{
Log.d("saveImage", "Exception 2, Something went wrong!");
e.printStackTrace();
}
}
2. Now we have a method to save bitmap into an image file in andorid, let’s write the AsyncTask for downloading images by url. This private class need to be placed in your Activity class as a subclass. After the image is downloaded, in the onPostExecute method, it calls the saveImage method defined above to save the image. Note, the image name is hardcoded as “my_image.png”.
private class DownloadImage extends AsyncTask<String, Void, Bitmap> {
private String TAG = "DownloadImage";
private Bitmap downloadImageBitmap(String sUrl) {
Bitmap bitmap = null;
try {
InputStream inputStream = new URL(sUrl).openStream(); // Download Image from URL
bitmap = BitmapFactory.decodeStream(inputStream); // Decode Bitmap
inputStream.close();
} catch (Exception e) {
Log.d(TAG, "Exception 1, Something went wrong!");
e.printStackTrace();
}
return bitmap;
}
@Override
protected Bitmap doInBackground(String... params) {
return downloadImageBitmap(params[0]);
}
protected void onPostExecute(Bitmap result) {
saveImage(getApplicationContext(), result, "my_image.png");
}
}
3. The AsyncTask for downloading the image is defined, but we need to execute it in order to run that AsyncTask. To do so, write this line in your onCreate method in your Activity class, or in an onClick method of a button or other places you see fit.
new DownloadImage().execute("http://developer.android.com/images/activity_lifecycle.png");
The image should be saved in /data/data/your.app.packagename/files/my_image.jpeg, check this post for accessing this directory from your device.
IMO this solves the issue! If you want further steps such as load the image you can follow these extra steps:
4. After the image is downloaded, we need a way to load the image bitmap from the internal storage, so we can use it. Let’s write the method for loading the image bitmap. This method takes two paramethers, a context and an image file name, without the full path, the context.openFileInput(imageName) will look up the file at the save directory when this file name was saved in the above saveImage method.
public Bitmap loadImageBitmap(Context context, String imageName) {
Bitmap bitmap = null;
FileInputStream fiStream;
try {
fiStream = context.openFileInput(imageName);
bitmap = BitmapFactory.decodeStream(fiStream);
fiStream.close();
} catch (Exception e) {
Log.d("saveImage", "Exception 3, Something went wrong!");
e.printStackTrace();
}
return bitmap;
}
5. Now we have everything we needed for setting the image of an ImageView or any other Views that you like to use the image on. When we save the image, we hardcoded the image name as “my_image.jpeg”, now we can pass this image name to the above loadImageBitmap method to get the bitmap and set it to an ImageView.
someImageView.setImageBitmap(loadImageBitmap(getApplicationContext(), "my_image.jpeg"));
6. To get the image full path by image name.
File file = getApplicationContext().getFileStreamPath("my_image.jpeg");
String imageFullPath = file.getAbsolutePath();
7. Check if the image file exists.
File file =
getApplicationContext().getFileStreamPath("my_image.jpeg");
if (file.exists()) Log.d("file", "my_image.jpeg exists!");
To delete the image file.
File file = getApplicationContext().getFileStreamPath("my_image.jpeg"); if (file.delete()) Log.d("file", "my_image.jpeg deleted!");
回答6:
this code perfectly run in my project
downloadImagesToSdCard(imagepath,imagepath);
private void downloadImagesToSdCard(String downloadUrl,String imageName)
{
try
{
URL url = new URL("www.xxx.com"+downloadUrl);
/* making a directory in sdcard */
// String sdCard=Environment.getExternalStorageDirectory().toString();
ContextWrapper cw = new ContextWrapper(getActivity());
// path to /data/data/yourapp/app_data/imageDir
File directory = cw.getDir("files", Context.MODE_PRIVATE);
File myDir = new File(directory,"folder");
/* if specified not exist create new */
if(!myDir.exists())
{
myDir.mkdir();
Log.v("", "inside mkdir");
}
/* checks the file and if it already exist delete */
String fname = imageName;
File file = new File (myDir, fname);
Log.d("file===========path", ""+file);
if (file.exists ())
file.delete ();
/* Open a connection */
URLConnection ucon = url.openConnection();
InputStream inputStream = null;
HttpURLConnection httpConn = (HttpURLConnection)ucon;
httpConn.setRequestMethod("GET");
httpConn.connect();
inputStream = httpConn.getInputStream();
/*if (httpConn.getResponseCode() == HttpURLConnection.HTTP_OK)
{
inputStream = httpConn.getInputStream();
}*/
FileOutputStream fos = new FileOutputStream(file);
int totalSize = httpConn.getContentLength();
int downloadedSize = 0;
byte[] buffer = new byte[1024];
int bufferLength = 0;
while ( (bufferLength = inputStream.read(buffer)) >0 )
{
fos.write(buffer, 0, bufferLength);
downloadedSize += bufferLength;
Log.i("Progress:","downloadedSize:"+downloadedSize+"totalSize:"+ totalSize) ;
}
fos.close();
Log.d("test", "Image Saved in sdcard..");
viewimage();
}
catch(IOException io)
{
io.printStackTrace();
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void viewimage()
{
String path = serialnumber+".png";
ContextWrapper cw = new ContextWrapper(getActivity());
//path to /data/data/yourapp/app_data/dirName
File directory = cw.getDir("files", Context.MODE_PRIVATE);
File mypath=new File(directory,"folder/"+path);
Bitmap b;
try {
b = BitmapFactory.decodeStream(new FileInputStream(mypath));
// b.compress(format, quality, stream)
profile_image.setImageBitmap(Bitmap.createScaledBitmap(b, 120, 120, false));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
回答7:
Try this
try
{
Bitmap bmp = null;
URL url = new URL("Your_URL");
URLConnection conn = url.openConnection();
bmp = BitmapFactory.decodeStream(conn.getInputStream());
File f = new File(Environment.getExternalStorageDirectory(),System.currentTimeMillis() + ".jpg");
if(f.exists())
f.delete();
f.createNewFile();
Bitmap bitmap = bmp;
ByteArrayOutputStream bos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 0 /*ignored for PNG*/, bos);
byte[] bitmapdata = bos.toByteArray();
FileOutputStream fos = new FileOutputStream(f);
fos.write(bitmapdata);
fos.flush();
fos.close();
Log.e(TAG, "imagepath: "+f );
}
catch (Exception e)
{
e.printStackTrace();
}
回答8:
public class testCrop extends AppCompatActivity {
ImageView iv;
String imagePath = "https://style.pk/wp-content/uploads/2015/07/omer-Shahzad-performed-umrah-600x548.jpg";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.testcrpop);
iv = (ImageView) findViewById(R.id.testCrop);
imageDownload image = new imageDownload(testCrop.this, iv);
image.execute(imagePath);
}
class imageDownload extends AsyncTask<String, Integer, Bitmap> {
Context context;
ImageView imageView;
Bitmap bitmap;
InputStream in = null;
int responseCode = -1;
//constructor.
public imageDownload(Context context, ImageView imageView) {
this.context = context;
this.imageView = imageView;
}
@Override
protected void onPreExecute() {
}
@Override
protected Bitmap doInBackground(String... params) {
try {
URL url = new URL(params[0]);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setDoOutput(true);
httpURLConnection.connect();
responseCode = httpURLConnection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
in = httpURLConnection.getInputStream();
bitmap = BitmapFactory.decodeStream(in);
in.close();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap data) {
imageView.setImageBitmap(data);
saveImage(data);
}
private void saveImage(Bitmap data) {
File createFolder = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),"test");
createFolder.mkdir();
File saveImage = new File(createFolder,"downloadimage.jpg");
try {
OutputStream outputStream = new FileOutputStream(saveImage);
data.compress(Bitmap.CompressFormat.JPEG,100,outputStream);
outputStream.flush();
outputStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
OUTPUT
Make sure you added permission to write data in memory
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
回答9:
As Google tells, for now, don't forget to add also readable on external storage in the manifest :
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
Source : http://developer.android.com/training/basics/data-storage/files.html#GetWritePermission
来源：https://stackoverflow.com/questions/15549421/how-to-download-and-save-an-image-in-android