AsyncImageLoader的思路:
1. 自定义RejectedExecutionHandler, 当线程任务被拒绝时,使其等待线程管理池空余后继续被调用。
2. 自定义线程管理池ThreadPoolExecutor替代ExecutorService
3. 线程的主要任务DownloadThreadTask,加载图片
4. 所有任务完成后,关闭自定义的ThreadPoolExecutor
源码:
自定义的RejectedExecutionHandler
public class RejectedExcutionHandlerImpl implements RejectedExecutionHandler { @Override public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) { Log.i("test", ((DownloadThreadTask)r).getTask() + " is rejected"); // 如果出现线程任务被拒绝,则等待一段时间后,再次创建并提交到线程池中 try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } executor.execute(r); Log.i("test",((DownloadThreadTask)r).getTask() + "再次创建并提交"); } }
自定义的ThreadPoolExecutor
public class CustomThreadPoolExecutor extends ThreadPoolExecutor { public CustomThreadPoolExecutor( int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler){ super(corePoolSize,maximumPoolSize, keepAliveTime, unit, workQueue, handler); } // beforeExecute, afterExecute方法一般用于日志中,记录任务被调用前和完成后的状态 @Override protected void beforeExecute(Thread t, Runnable r) { super.beforeExecute(t, r); Log.i("test","perform before execute logic" + ((DownloadThreadTask)r).getTask()); } @Override protected void afterExecute(Runnable r, Throwable t) { super.afterExecute(r, t); if (t != null) { Log.i("test","Perform exception handler logic" + ((DownloadThreadTask)r).getTask()); } Log.i("test","Perform afterExecute() logic" + ((DownloadThreadTask)r).getTask()); } }
线程任务DownloadThreadTask
public class DownloadThreadTask implements Runnable { public Map<String, SoftReference<Drawable>> imageCache = new HashMap<String,SoftReference<Drawable>>(); private String task; // 任务名称 private String url; // 加载URL private Handler handler; private ImageCallback callback; public DownloadThreadTask(String task, String url, Handler handler, ImageCallback callback){ this.task = task; this.url = url; this.handler = handler; this.callback = callback; } public String getTask() { return task; } public void setTask(String task) { this.task = task; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public Handler getHandler() { return handler; } public void setHandler(Handler handler) { this.handler = handler; } @Override public void run() { try { try{ Thread.sleep(10); }catch(InterruptedException e){ e.printStackTrace(); } final Drawable drawable = loadImageFromUrl(url); imageCache.put(url, new SoftReference<Drawable>(drawable)); handler.post(new Runnable() { public void run() { callback.imageLoader(drawable); } }); Log.i("test", "加载图片任务完成" + this.task); } catch (Exception e) { throw new RuntimeException(e); } } protected Drawable loadImageFromUrl(String imageUrl){ try { return Drawable.createFromStream(new URL(imageUrl).openStream(), "image.png"); } catch (Exception e) { throw new RuntimeException(e); } } }
AsyncImageLoader
public class AsyncImageLoader { public Map<String, SoftReference<Drawable>> imageCache = new HashMap<String,SoftReference<Drawable>>(); private BlockingQueue<Runnable> blockingQueue = new ArrayBlockingQueue<Runnable>(2); private RejectedExecutionHandler myReject = new RejectedExcutionHandlerImpl(); CustomThreadPoolExecutor executor = new CustomThreadPoolExecutor(1,2,5,TimeUnit.MILLISECONDS, blockingQueue, myReject); private final Handler handler = new Handler(); public Drawable loadDrawable(final String task, final String imageUrl, final ImageCallback callback){ if(imageCache.containsKey(imageUrl)){ SoftReference<Drawable> softReference = imageCache.get(imageUrl); if(softReference.get()!=null){ return softReference.get(); } } Log.i("test","创建任务并提交到线程池中:" + task); executor.execute(new DownloadThreadTask(task, imageUrl, handler, callback)); try { Thread.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } return null; } public void shutdownAndAwaitTermination() { executor.shutdown(); // Disable new tasks from being submitted try { // Wait a while for existing tasks to terminate if (!executor.awaitTermination(60, TimeUnit.SECONDS)) { executor.shutdownNow(); // Cancel currently executing tasks // Wait a while for tasks to respond to being cancelled Log.i("test", "i am shutting down..."); if (!executor.awaitTermination(60, TimeUnit.SECONDS)) System.err.println("Pool did not terminate"); } }catch (InterruptedException ie) { // (Re-)Cancel if current thread also interrupted Log.e("test","something interrupted happend, and i am shutting down...."); executor.shutdownNow(); // Preserve interrupt status //Thread.currentThread().interrupt(); } } }
下载的Activity对AsyncImageLoader的调用
public class BatchDownloadActivity extends Activity { private static final String fileRealName = "我的图片1.gif"; private String url; private int id; private List<String> urls = new ArrayList<String>(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.batch_download); String fileName = fileRealName; String url = ""; try { url = ToolsUtil.getIpAddress() + URLEncoder.encode(fileRealName,"UTF-8"); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } Log.i("test","url=" + url); loadImage("task@1", url, R.id.imageView1); loadImage("task@2", url, R.id.imageView2); loadImage("task@3", url, R.id.imageView3); loadImage("task@4", url,R.id.imageView4); loadImage("task$5", url,R.id.imageView5); loader.shutdownAndAwaitTermination(); } private AsyncImageLoader loader = new AsyncImageLoader(); private void loadImage(final String task, final String url, final int id) { Drawable cacheImage = loader.loadDrawable(task, url,new ImageCallback() { @Override public void imageLoader(Drawable imageDrawable) { ((ImageView) findViewById(id)).setImageDrawable(imageDrawable); Log.i(task, "loading new pic:" +url); } }); if (cacheImage != null) { ((ImageView) findViewById(id)).setImageDrawable(cacheImage); Log.i("test", "loading existing pic"); } } }
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以下使用 Callable 替代Runnable来进行图片的加载。 思路如上述所,只是修改一些源码。
1. 加载图片的 Callable
public class DownloadCallableTask implements Callable<Drawable> { public Map<String, SoftReference<Drawable>> imageCache = new HashMap<String,SoftReference<Drawable>>(); private String task; private String url; public DownloadCallableTask(String task, String url){ this.task = task; this.url = url; } public String getTask(){ return this.task; } @Override public Drawable call() throws Exception { try{ Thread.sleep(10); }catch(InterruptedException e){ e.printStackTrace(); } if(imageCache.containsKey(url)){ SoftReference<Drawable> softReference = imageCache.get(url); if(softReference.get()!=null){ return softReference.get(); } } final Drawable drawable = loadImageFromUrl(url); imageCache.put(url, new SoftReference<Drawable>(drawable)); Log.i("test", "加载图片任务完成" + this.task); return drawable; } protected Drawable loadImageFromUrl(String imageUrl){ try { return Drawable.createFromStream(new URL(imageUrl).openStream(), "image.png"); } catch (Exception e) { throw new RuntimeException(e); } } }
2. AsyncCallableLoader 替代 AsyncImageLoader
public class AsyncCallableLoader { private BlockingQueue<Runnable> blockingQueue = new ArrayBlockingQueue<Runnable>(2); ThreadPoolExecutor executor = new ThreadPoolExecutor(1,2,5,TimeUnit.MILLISECONDS, blockingQueue); private final Handler handler = new Handler(); public Drawable loadDrawable(final String task, final String imageUrl) throws InterruptedException, ExecutionException{ Log.i("test","创建任务并提交到线程池中:" + task); final Future<Drawable> future = executor.submit(new DownloadCallableTask(task,imageUrl)); try { Thread.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } return future.get(); } public void shutdownAndAwaitTermination() { executor.shutdown(); // Disable new tasks from being submitted try { // Wait a while for existing tasks to terminate if (!executor.awaitTermination(60, TimeUnit.SECONDS)) { executor.shutdownNow(); // Cancel currently executing tasks // Wait a while for tasks to respond to being cancelled Log.i("test", "i am shutting down..."); if (!executor.awaitTermination(60, TimeUnit.SECONDS)) System.err.println("Pool did not terminate"); } }catch (InterruptedException ie) { // (Re-)Cancel if current thread also interrupted Log.e("test","something interrupted happend, and i am shutting down...."); executor.shutdownNow(); // Preserve interrupt status //Thread.currentThread().interrupt(); } } }
3. Activity调用AsnycCallableLoader
private AsyncCallableLoader loader = new AsyncCallableLoader(); private void loadImage(final String task, final String url, final int id) { Drawable cacheImage; try { cacheImage = loader.loadDrawable(task, url); if (cacheImage != null) { ((ImageView) findViewById(id)).setImageDrawable(cacheImage); Log.i("test", "loading pic"); } } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } }