方法一、直接通过Android官方提供的Http类访来问远程服务器,这里AndroidHttpClient是SDK 2.2中新出的方法,API Level为8,大家需要注意下,静态访问可以直接调用,如果SDK版本较低可以考虑Apache的Http库,当然HttpURLConnection或URLConnection也可以。
- static Bitmap downloadBitmapByCwj(String url) {
- final AndroidHttpClient client = AndroidHttpClient.newInstance("linux初学三月");
- final HttpGet getRequest = new HttpGet(url);
- try {
- HttpResponse response = client.execute(getRequest);
- final int statusCode = response.getStatusLine().getStatusCode();
- if (statusCode != HttpStatus.SC_OK) {
- Log.e("cwjDebug", "Error " + statusCode + " while retrieving bitmap from " + url);
- return null;
- }
-
- final HttpEntity entity = response.getEntity();
- if (entity != null) {
- InputStream inputStream = null;
- try {
- inputStream = entity.getContent();
- final Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
- return bitmap;
- } finally {
- if (inputStream != null) {
- inputStream.close();
- }
- entity.consumeContent();
- }
- }
- } catch (Exception e) {
- getRequest.abort();
- Log.e("Debug", "Error while retrieving bitmap from " + url, e.toString());
- } finally {
- if (client != null) {
- client.close();
- }
- }
- return null;
- }
- static class FlushedInputStream extends FilterInputStream {
- public FlushedInputStream(InputStream inputStream) {
- super(inputStream);
- }
- @Override
- public long skip(long n) throws IOException {
- long totalBytesSkipped = 0L;
- while (totalBytesSkipped < n) {
- long bytesSkipped = in.skip(n - totalBytesSkipped);
- if (bytesSkipped == 0L) {
- int byte = read();
- if (byte < 0) {
- break; // we reached EOF
- } else {
- bytesSkipped = 1; // we read one byte
- }
- }
- totalBytesSkipped += bytesSkipped;
- }
- return totalBytesSkipped;
- }
- }
从Android 1.5固件开发平台开始Google提供了一个AsyncTask类来帮助开发者处理异步下载的实现,相对于Thread线程而言他可以运行在UI线程中,其内部的实现是从Java 5开始的并发包concurrent中派生而来的,总体实现比较可靠就是资源占用略大了些。不过使用起来比简单。这里下载图片类ImageDownloader类的download方法可以很好的处理实现UI显示等操作,参数一url为远程server上文件的url,第二个参数为imageview对象,可以直接让imageview显示出下载的远程图片。
- public class ImageDownloader {
- public void download(String url, ImageView imageView) {
- BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
- task.execute(url);
- }
- }
- }
- class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
- private String url;
- private final WeakReference<ImageView> imageViewReference; //使用WeakReference解决内存问题
- public BitmapDownloaderTask(ImageView imageView) {
- imageViewReference = new WeakReference<ImageView>(imageView);
- }
- @Override
- protected Bitmap doInBackground(String... params) { //实际的下载线程,内部其实是concurrent线程,所以不会阻塞
-
- return downloadBitmap(params[0]);
- }
- @Override
- protected void onPostExecute(Bitmap bitmap) { //下载完后执行的
- if (isCancelled()) {
- bitmap = null;
- }
- if (imageViewReference != null) {
- ImageView imageView = imageViewReference.get();
- if (imageView != null) {
- imageView.setImageBitmap(bitmap); //下载完设置imageview为刚才下载的bitmap对象
- }
- }
- }
- }