关于ExecutorService的使用

ExecutorService： 线程池， 顾名思义是一个调度线程运行的管理池。 我预制了一个场景： 在界面上，有5个图片需要进行异步加载， 我们使用了一个线程池管理类 AsyncImageLoader来控制加载图片的线程个数，如果加载的图片原本已经存在，则从系统中调出已有图片进行加载； 如果图片是首次加载，则通过连接加载图片。

1. 需要加载5个图片的界面：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical" android:layout_width="fill_parent"
 android:layout_height="fill_parent">
 
 	<TextView 
 	    android:text="图片区域开始" 
 	    android:id="@+id/textView2"
 		android:layout_width="wrap_content" 
 		android:layout_height="wrap_content">
 	</TextView>

 	<ImageView 
 	    android:id="@+id/imageView1"
 		android:layout_height="wrap_content" 
 		android:src="@drawable/ic_launcher"
 		android:layout_width="wrap_content">
 	</ImageView>
	
	<ImageView 
	    android:id="@+id/imageView2"
 		android:layout_height="wrap_content" 
 		android:src="@drawable/ic_launcher"
 		android:layout_width="wrap_content">
	</ImageView>

	<ImageView 
	    android:id="@+id/imageView3"
 		android:layout_height="wrap_content" 
 		android:src="@drawable/ic_launcher"
 		android:layout_width="wrap_content">
	</ImageView>

	<ImageView 
	    android:id="@+id/imageView4"
 		android:layout_height="wrap_content" 
 		android:src="@drawable/ic_launcher"
 		android:layout_width="wrap_content">
	</ImageView>

	<ImageView 
	    android:id="@+id/imageView5"
 		android:layout_height="wrap_content" 
 		android:src="@drawable/ic_launcher"
 		android:layout_width="wrap_content">
	</ImageView>
 	
 	<TextView 
 	    android:text="图片区域结束" 
 	    android:id="@+id/textView1"
 		android:layout_width="wrap_content" 
 		android:layout_height="wrap_content">
 	</TextView>
</LinearLayout>

2. AsyncImageLoader类

public class AsyncImageLoader {
	
	public Map<String, SoftReference<Drawable>> imageCache = new HashMap<String,SoftReference<Drawable>>();

        // 线程池的数量设置：在次，设置同时运行3个线程。 
	private ExecutorService executorService = Executors.newFixedThreadPool(3);
	
	private final Handler handler = new Handler();
	
	public ExecutorService getExecutorService() {
		return executorService;
	}

	public void setExecutorService(ExecutorService executorService) {
		this.executorService = executorService;
	}

	public Drawable loadDrawable(final String imageUrl, final ImageCallback callback){
		// 如果缓存中已经加载过该图片，则调用缓存中的图片加载
		if(imageCache.containsKey(imageUrl)){
			SoftReference<Drawable> softReference = imageCache.get(imageUrl);
			
			if(softReference.get()!=null){
				return softReference.get();
			}
		}
		
                // 首次加载图片的方法，使用线程池调用加载图片的线程
		executorService.submit(new Runnable(){

			@Override
			public void run() {
			
				try {  
                    // 加载图片
                    final Drawable drawable = loadImageFromUrl(imageUrl);
                    // 将图片的加载路径保存到缓存中
                    imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
                    // 图片加载完成后， 在界面中显示被加载的图片
                    handler.post(new Runnable() {  
                        public void run() {  
                            callback.imageLoader(drawable);
                        }  
                    });  
                } catch (Exception e) {  
                    throw new RuntimeException(e);  
                }  
			}
			
		});
		
		
		return null;
	}
	
	protected Drawable loadImageFromUrl(String imageUrl){
		 try {  
            return Drawable.createFromStream(new URL(imageUrl).openStream(), "image.png");  
     } catch (Exception e) {  
             throw new RuntimeException(e);  
     }  
		
	}
	public interface ImageCallback{
		public void imageLoader(Drawable imageDrawable);
	}

        // 关闭线程池	
	public void shutdownAndAwaitTermination(ExecutorService pool) {
                   // 关闭线程池，新的任务就不再运行
		   pool.shutdown(); // Disable new tasks from being submitted

		   try {
		     // Wait a while for existing tasks to terminate
                     // 设置一个等待时间，使原来已经存在的任务完成其工作
		     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
                    
		    	 pool.shutdownNow(); // Cancel currently executing tasks
			       // Wait a while for tasks to respond to being cancelled
		    	 Log.i("test", "i am shutting down...");
			       if (!pool.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....");
		     pool.shutdownNow();
		     // Preserve interrupt status
		     Thread.currentThread().interrupt();
		  }
	 }
}

3. 对AsyncImageLoader的调用异步加载这5个图片

public class BatchDownloadActivity extends Activity {

       //需要加载的图片名称	
	private static final String fileRealName = "我的图片1.gif";
	private String url;
	private int id;
	

	@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();
		}
                // url： http://xx.xx.xx.xx:port/webapp/filename.gif
		
		Log.i("test","url=" + url);
		
                // 调用加载图片方法
		loadImage(url, R.id.imageView1);
		loadImage(url, R.id.imageView2);
		loadImage(url, R.id.imageView3);
		loadImage(url,R.id.imageView4);
		loadImage(url,R.id.imageView5);
		
                //加载完成后，关闭线程管理池
		loader.shutdownAndAwaitTermination(loader.getExecutorService());
	
	}
	
	private AsyncImageLoader loader = new AsyncImageLoader();

	private void loadImage(final String url, final int id) {
		
		Drawable cacheImage = loader.loadDrawable(url,new AsyncImageLoader.ImageCallback() {  
				@Override
					public void imageLoader(Drawable imageDrawable) {
						
					     ((ImageView) findViewById(id)).setImageDrawable(imageDrawable);
					     Log.i("test", "loading new pic");
					}  
        });  

		if (cacheImage != null) {  
			((ImageView) findViewById(id)).setImageDrawable(cacheImage);  
			Log.i("test", "loading existing pic");
		}  
		
	}

}