Android 远程图片获取和本地缓存（三）

从缓存中获取数据：

java代码：

/**

* 从缓存中获取图片

*/

private Bitmap getBitmapFromCache(Stringurl) {

// 先从mHardBitmapCache缓存中获取

synchronized (mHardBitmapCache) {

final Bitmap bitmap =mHardBitmapCache.get(url);

if (bitmap != null) {

//如果找到的话，把元素移到linkedhashmap的最前面，从而保证在LRU算法中是最后被删除

mHardBitmapCache.remove(url);

mHardBitmapCache.put(url,bitmap);

return bitmap;

}

}

//如果mHardBitmapCache中找不到，到mSoftBitmapCache中找

SoftReference<Bitmap>bitmapReference = mSoftBitmapCache.get(url);

if (bitmapReference != null) {

final Bitmap bitmap =bitmapReference.get();

if (bitmap != null) {

return bitmap;

} else {

mSoftBitmapCache.remove(url);

}

}

return null;

}

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如果缓存中不存在，那么就只能去服务器端去下载：

java代码：

/**

* 异步下载图片

*/

class ImageDownloaderTask extendsAsyncTask<String, Void, Bitmap> {

private static final int IO_BUFFER_SIZE= 4 * 1024;

private String url;

private finalWeakReference<ImageView> imageViewReference;

public ImageDownloaderTask(ImageViewimageView) {

imageViewReference = newWeakReference<ImageView>(imageView);

}

@Override

protected BitmapdoInBackground(String... params) {

final AndroidHttpClient client =AndroidHttpClient.newInstance("Android");

url = params[0];

final HttpGet getRequest = newHttpGet(url);

try {

HttpResponse response =client.execute(getRequest);

final int statusCode =response.getStatusLine().getStatusCode();

if (statusCode !=HttpStatus.SC_OK) {

Log.w(TAG, "从" +url + "中下载图片时出错!,错误码:" + statusCode);

return null;

}

final HttpEntity entity =response.getEntity();

if (entity != null) {

InputStream inputStream =null;

OutputStream outputStream =null;

try {

inputStream =entity.getContent();

finalByteArrayOutputStream dataStream = new ByteArrayOutputStream();

outputStream = newBufferedOutputStream(dataStream, IO_BUFFER_SIZE);

copy(inputStream,outputStream);

outputStream.flush();

final byte[] data =dataStream.toByteArray();

final Bitmap bitmap =BitmapFactory.decodeByteArray(data, 0, data.length);

return bitmap;

} finally {

if (inputStream !=null) {

inputStream.close();

}

if (outputStream !=null) {

outputStream.close();

}

entity.consumeContent();

}

}

} catch (IOException e) {

getRequest.abort();

Log.w(TAG, "I/O errorwhile retrieving bitmap from " + url, e);

} catch (IllegalStateException e) {

getRequest.abort();

Log.w(TAG, "Incorrect URL:" + url);

} catch (Exception e) {

getRequest.abort();

Log.w(TAG, "Error whileretrieving bitmap from " + url, e);

} finally {

if (client != null) {

client.close();

}

}

return null;

}

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系列之Android 远程图片获取和本地缓存（一）的帖子链接http://www.eoeandroid.com/thread-98446-1-1.html
系列之Android 远程图片获取和本地缓存（二）的帖子链接http://www.eoeandroid.com/thread-98449-1-1.html