Android Asynchronous HTTPClient的实现和优化

bobboy00

2011-11-02

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大家知道Android对UI线程的反应时间要求很高，超过5秒钟直接ANR掉，根本不给你机会多等。

而Android应用与后端系统的交互是最基本的需求之一，如何实现高效的Asynchronous HTTPClient，确保UI线程在启动任务后交由后端异步处理与服务器端的通信，尤为关键。

Google过几个方案，要么太复杂要么不符合要求，基本都淘汰了，最后发现这一版本的实现不错，就拿来用了。

链接：Android Asynchronous HTTPClient tutorial

后来发现了几个严重的问题，罗列如下：

1. 启用单独的线程后，简直如脱缰的野马，难以驾驭。

现象是：在调试的时候经常发现某个线程死掉（比如在服务器down掉的时候，由于线程无法连接而挂掉）

后果是：只能关掉模拟器，甚至还要重启eclipse，否者两者通信出现问题，再也不能继续联机调试

2. 异常的处理非常弱，Activity层难以捕捉并加以处理。

这个问题跟实现的机制有一定的关系，此实现根本就没提供好的异常处理机制，以便捕捉、反馈、处理合理的可预见性的异常，诸如：

1）UnknownHostException – 谁能确保手机的网络连接一直正常，信号一直满格？

2）HttpResponseException – 后端500的错误，说不定就蹦出来了

3）SocketTimeoutException – 超时也是太正常不过了，如果人家在荒山野岭（no 3G）摆弄超大的通信请求

4）诸如此类吧

所以改造就再说难免了。下面我贴出相关代码（import就省了吧这里），并加以简单注释说明，方面大家的理解。

首先定义AsyncHttpClient.java。这里的重点是超时的设置。另外我加了个cancelRequest，用以在切换Activity后取消掉原有Activity发出的所有的异步请求，因为一般情况下，切换了Activity后是不能再更新那个UI了，否则会抛出异常，直接导致应用crash掉，不过话说回来，这个cancel我发现好像不是那么给力(any feedback?)。

public class AsyncHttpClient {
	private static DefaultHttpClient httpClient;
	
	public static int CONNECTION_TIMEOUT = 2*60*1000;
	public static int SOCKET_TIMEOUT  = 2*60*1000;
	
	private static ConcurrentHashMap<Activity,AsyncHttpSender> tasks = new ConcurrentHashMap<Activity,AsyncHttpSender>();
		
	public static void sendRequest(
			final Activity currentActitity,
			final HttpRequest request,
			AsyncResponseListener callback) {
		
		sendRequest(currentActitity, request, callback, CONNECTION_TIMEOUT, SOCKET_TIMEOUT);
	}
	
	public static void sendRequest(
			final Activity currentActitity,
			final HttpRequest request,
			AsyncResponseListener callback,
			int timeoutConnection,
			int timeoutSocket) {
		
		InputHolder input = new InputHolder(request, callback);
		AsyncHttpSender sender = new AsyncHttpSender();
		sender.execute(input);
		tasks.put(currentActitity, sender);
	}
	
	public static void cancelRequest(final Activity currentActitity){
		if(tasks==null || tasks.size()==0) return;
		for (Activity key : tasks.keySet()) {
		    if(currentActitity == key){
		    	AsyncTask<?,?,?> task = tasks.get(key);
		    	if(task.getStatus()!=null && task.getStatus()!=AsyncTask.Status.FINISHED){
			    	Log.i(TAG, "AsyncTask of " + task + " cancelled.");
		    		task.cancel(true);
		    	}
		    	tasks.remove(key);
		    }
		}
	}
 
	public static synchronized HttpClient getClient() {
		if (httpClient == null){			
			//use following code to solve Adapter is detached error
			//refer: http://stackoverflow.com/questions/5317882/android-handling-back-button-during-asynctask
			BasicHttpParams params = new BasicHttpParams();
			
			SchemeRegistry schemeRegistry = new SchemeRegistry();
			schemeRegistry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
			final SSLSocketFactory sslSocketFactory = SSLSocketFactory.getSocketFactory();
			schemeRegistry.register(new Scheme("https", sslSocketFactory, 443));
			
			// Set the timeout in milliseconds until a connection is established.
			HttpConnectionParams.setConnectionTimeout(params, CONNECTION_TIMEOUT);
			// Set the default socket timeout (SO_TIMEOUT) 
			// in milliseconds which is the timeout for waiting for data.
			HttpConnectionParams.setSoTimeout(params, SOCKET_TIMEOUT);
			
			ClientConnectionManager cm = new ThreadSafeClientConnManager(params, schemeRegistry);
			httpClient = new DefaultHttpClient(cm, params);	
		}
		return httpClient;
	}
 
}

然后是AsyncHttpSender。这里我用了InputHolder和OutputHolder来进行对象传递，简单包装了下：

/**
 * AsyncHttpSender is the AsyncTask implementation
 * 
 * @author bright_zheng
 *
 */
public class AsyncHttpSender extends AsyncTask<InputHolder, Void, OutputHolder> {

	@Override
	protected OutputHolder doInBackground(InputHolder... params) {
		HttpEntity entity = null;
		InputHolder input = params[0];
		try {
			HttpResponse response = AsyncHttpClient.getClient().execute((HttpUriRequest) input.getRequest());
			StatusLine status = response.getStatusLine();
			
	        if(status.getStatusCode() >= 300) {
	        	return new OutputHolder(
	        			new HttpResponseException(status.getStatusCode(), status.getReasonPhrase()),
	        			input.getResponseListener());
	        }
	        
			entity = response.getEntity();
			Log.i(TAG, "isChunked:" + entity.isChunked());
            if(entity != null) {
            	try{
            		entity = new BufferedHttpEntity(entity);
            	}catch(Exception e){
            		Log.e(TAG, e.getMessage(), e);
            		//ignore?
            	}
            }			
		} catch (ClientProtocolException e) {
			Log.e(TAG, e.getMessage(), e);
			return new OutputHolder(e, input.getResponseListener());
		} catch (IOException e) {
			Log.e(TAG, e.getMessage(), e);
			return new OutputHolder(e, input.getResponseListener());
		}
		return new OutputHolder(entity, input.getResponseListener());
	}
	
	@Override
    protected void onPreExecute(){
		Log.i(TAG, "AsyncHttpSender.onPreExecute()");
		super.onPreExecute();
	}
	
	@Override
	protected void onPostExecute(OutputHolder result) {
		Log.i(TAG, "AsyncHttpSender.onPostExecute()");
		super.onPostExecute(result);
		
		if(isCancelled()){
			Log.i(TAG, "AsyncHttpSender.onPostExecute(): isCancelled() is true");
			return; //Canceled, do nothing
		}
		
		AsyncResponseListener listener = result.getResponseListener();
		HttpEntity response = result.getResponse();
		Throwable exception = result.getException();
		if(response!=null){
			Log.i(TAG, "AsyncHttpSender.onResponseReceived(response)");
			listener.onResponseReceived(response);
		}else{
			Log.i(TAG, "AsyncHttpSender.onResponseReceived(exception)");
			listener.onResponseReceived(exception);
		}
	}
	
	@Override
    protected void onCancelled(){
		Log.i(TAG, "AsyncHttpSender.onCancelled()");
		super.onCancelled();
		//this.isCancelled = true;
	}
}

/**
 * Input holder
 * 
 * @author bright_zheng
 *
 */
public class InputHolder{
	private HttpRequest request;
	private AsyncResponseListener responseListener;
	
	public InputHolder(HttpRequest request, AsyncResponseListener responseListener){
		this.request = request;
		this.responseListener = responseListener;
	}
	
	
	public HttpRequest getRequest() {
		return request;
	}

	public AsyncResponseListener getResponseListener() {
		return responseListener;
	}
}

public class OutputHolder{
	private HttpEntity response;
	private Throwable exception;
	private AsyncResponseListener responseListener;
	
	public OutputHolder(HttpEntity response, AsyncResponseListener responseListener){
		this.response = response;
		this.responseListener = responseListener;
	}
	
	public OutputHolder(Throwable exception, AsyncResponseListener responseListener){
		this.exception = exception;
		this.responseListener = responseListener;
	}

	public HttpEntity getResponse() {
		return response;
	}

	public Throwable getException() {
		return exception;
	}
	
	public AsyncResponseListener getResponseListener() {
		return responseListener;
	}
	
}

再来看看我们的Call back接口定义, AsyncResponseListener.java：

/**
 * The call back interface for  
 * 
 * @author bright_zheng
 *
 */
public interface AsyncResponseListener {
	/** Handle successful response */
	public void onResponseReceived(HttpEntity response);
	
	/** Handle exception */
	public void onResponseReceived(Throwable response);
}

以及抽象Call back的实现，AbstractAsyncResponseListener.java：

/**
 * Abstract Async Response Listener implementation
 * 
 * Subclass should implement at lease two methods.
 * 1. onSuccess() to handle the corresponding successful response object
 * 2. onFailure() to handle the exception if any
 * 
 * @author bright_zheng
 *
 */
public abstract class AbstractAsyncResponseListener implements AsyncResponseListener{
	public static final int RESPONSE_TYPE_STRING = 1;
	public static final int RESPONSE_TYPE_JSON_ARRAY = 2;
	public static final int RESPONSE_TYPE_JSON_OBJECT = 3;
	public static final int RESPONSE_TYPE_STREAM = 4;
	private int responseType;
	
	public AbstractAsyncResponseListener(){
		this.responseType = RESPONSE_TYPE_STRING; // default type
	}
	
	public AbstractAsyncResponseListener(int responseType){
		this.responseType = responseType;
	}
	
	public void onResponseReceived(HttpEntity response){
		try {
			switch(this.responseType){
		        case RESPONSE_TYPE_JSON_ARRAY:{
		        	String responseBody = EntityUtils.toString(response);	
		        	Log.i(TAG, "Return JSON String: " + responseBody);
		        	JSONArray json = null;
		        	if(responseBody!=null && responseBody.trim().length()>0){
		        		json = (JSONArray) new JSONTokener(responseBody).nextValue();
		        	}
		    		onSuccess(json);
		        	break;
		        }
		        case RESPONSE_TYPE_JSON_OBJECT:{
		        	String responseBody = EntityUtils.toString(response);	
		        	Log.i(TAG, "Return JSON String: " + responseBody);
		        	JSONObject json = null;
		        	if(responseBody!=null && responseBody.trim().length()>0){
		        		json = (JSONObject) new JSONTokener(responseBody).nextValue();
		        	}
		    		onSuccess(json);	
		        	break;
		        }
		        case RESPONSE_TYPE_STREAM:{
		        	onSuccess(response.getContent());
		        	break;
		        }
		        default:{
		        	String responseBody = EntityUtils.toString(response);
		        	onSuccess(responseBody);
		        }         
			}
	    } catch(IOException e) {
	    	onFailure(e);
	    } catch (JSONException e) {
	    	onFailure(e);
		}	
	}
	
	public void onResponseReceived(Throwable response){
		onFailure(response);
	}
	
	protected void onSuccess(JSONArray response){}
	
	protected void onSuccess(JSONObject response){}
	
	protected void onSuccess(InputStream response){}
	
	protected void onSuccess(String response) {}

	protected void onFailure(Throwable e) {}
}

这样我们使用起来就非常清晰、简单了。

下面贴个简单的客户端用法代码片段：

1、这个是把服务器端响应当stream用的，用以诸如文件、图片下载之类的场景：

AsyncHttpClient.sendRequest(this, request,  
        		new AbstractAsyncResponseListener(AbstractAsyncResponseListener.RESPONSE_TYPE_STREAM){
			
			@Override
			protected void onSuccess(InputStream response){
				Bitmap bmp = null;
				try {
					//bmp = decodeFile(response, _facial.getWidth());
					bmp = BitmapFactory.decodeStream(response);
					
					//resize to fit screen
					bmp = resizeImage(bmp, _facial.getWidth(), true);
	        		
					candidateCache.put(candidate_id, bmp);
	        		((ImageView) v).setImageBitmap(bmp);
	        		
	        		dialog.dismiss();
				} catch (Exception e) {
					onFailure(e);
				}
			}
			
			@Override
			protected void onFailure(Throwable e) {
				Log.i(TAG, "Error: " + e.getMessage(), e);
				updateErrorMessage(e);
				
				dialog.dismiss();
			}
			
		});

2、这个是把服务器端响应当JSON用的，用以诸如获取基本文本信息之类的场景：

// Async mode to get hit result
AsyncHttpClient.sendRequest(this, request, 
        		new AbstractAsyncResponseListener(AbstractAsyncResponseListener.RESPONSE_TYPE_JSON_ARRAY){

			@Override
			protected void onSuccess(JSONArray response){
				Log.i(TAG, "UploadAndMatch.onSuccess()...");
				candidates = response;
				if(candidates!=null && candidates.length()>0){
	        		hit_count = candidates.length();
	    	        Log.i(TAG, "HIT: " + hit_count);
	    	        updateStatus(String.format(context.getString(R.string.msg_got_hit), hit_count));
		        	
					//update UI
		        	refreshCurrentUI(1);
	        	}else{
	    	        Log.i(TAG, "No HIT!");
	    	        updateStatus(context.getString(R.string.msg_no_hit));
		        	
					//update UI
		        	refreshCurrentUI(0);
	        	}
			}
			
			@Override
			protected void onFailure(Throwable e) {
				Log.e(TAG, "UploadAndMatch.onFailure(), error: " + e.getMessage(), e);
				updateErrorMessage(e);
				//update UI
	        	refreshCurrentUI(-1);
			}
			
		});

欢迎拍砖，谢谢！

httpclient 线程