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[转载]Android Asynchronous HTTPClient的实现和优化-Android开发实例教程-eoe Android开发者社区_Android开发论坛.
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 (如果链接错误，请到网上搜索一下)
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: [url=http://stackoverflow.com/questions/5317882/android-handling-back-button-during-asynctask]http://stackoverflow.com/questions/5317882/android-handling-back-button-during-asynctask[/url]
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> {[/size]
@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(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, e.getMessage(), e);
//ignore?
}
}
} catch (ClientProtocolException e) {
Log.e(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, e.getMessage(), e);
return new OutputHolder(e, input.getResponseListener());
} catch (IOException e) {
Log.e(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, e.getMessage(), e);
return new OutputHolder(e, input.getResponseListener());
}
return new OutputHolder(entity, input.getResponseListener());
}
@Override
protected void onPreExecute(){
Log.i(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "AsyncHttpSender.onPreExecute()");
super.onPreExecute();
}
@Override
protected void onPostExecute(OutputHolder result) {
Log.i(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "AsyncHttpSender.onPostExecute()");
super.onPostExecute(result);
if(isCancelled()){
Log.i(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "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(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "AsyncHttpSender.onResponseReceived(response)");
listener.onResponseReceived(response);
}else{
Log.i(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "AsyncHttpSender.onResponseReceived(exception)");
listener.onResponseReceived(exception);
}
}
@Override
protected void onCancelled(){
Log.i(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "AsyncHttpSender.onCancelled()");
super.onCancelled();
//this.isCancelled = true;
}
}
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(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "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(<SPAN style="BACKGROUND-COLOR: #ffffff">TAG</SPAN>, "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) {}[/size]
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);
}
});
取自：http://www.iteye.com/topic/1117362
