AsyncHttpClient 源碼分析，asynchttpclient源碼

AsyncHttpClient 源碼分析，asynchttpclient源碼

開源的AsyncHttp是基於Apache HTTP Client封裝的一個庫，比較簡單，回調進行擷取資料，不用自己處理線程和執行個體化Handler

上一篇寫了個 AsyncHttpClient 擷取圖片和網頁資料示範 簡單用法

AsyncHttpClient.java 是暴露的介面，最主要的就是Post和Get 2種,還有其他的HTTP請求方式 比如還有Delete，Patch操作，不是很常用

線程池用的是 Executors.newCachedThreadPool() 這個源碼裡面顯示 核心線程是0，建立的線程60秒後不用就銷毀，感覺比較符合網路頻繁操作一段時間，

比如ListView非同步下載Bitmap圖片

  public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
  }
    
RequestHandle 返回的請求運行對象，可以cancel一個請求 ,但不一定能成功。

建立非同步請求用於任務執行

protected AsyncHttpRequest newAsyncHttpRequest(DefaultHttpClient client, HttpContext httpContext, HttpUriRequest uriRequest, String contentType, ResponseHandlerInterface responseHandler, Context context) {     return new AsyncHttpRequest(client, httpContext, uriRequest, responseHandler);}//發送請求    protected RequestHandle sendRequest(DefaultHttpClient client, HttpContext httpContext, HttpUriRequest uriRequest, String contentType, ResponseHandlerInterface responseHandler, Context context) {        //判斷代碼省去。。。。。只看關鍵的        if (contentType != null) {            if (uriRequest instanceof HttpEntityEnclosingRequestBase && ((HttpEntityEnclosingRequestBase) uriRequest).getEntity() != null) {                Log.w(LOG_TAG, "Passed contentType will be ignored because HttpEntity sets content type");            } else {                uriRequest.setHeader(HEADER_CONTENT_TYPE, contentType);            }        }        responseHandler.setRequestHeaders(uriRequest.getAllHeaders());        responseHandler.setRequestURI(uriRequest.getURI());     //構造一個請求對象，線程運行        AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest, contentType, responseHandler, context);        threadPool.submit(request);//提交任務                RequestHandle requestHandle = new RequestHandle(request);                   //這個地方用來判斷之前是否有請求，回收不必要的請求對象,因為RequestHandle可以取消任務，用的是Weak對象        if (context != null) {            // Add request to request map            List<RequestHandle> requestList = requestMap.get(context);            synchronized (requestMap) {                if (requestList == null) {                    requestList = Collections.synchronizedList(new LinkedList<RequestHandle>());                    requestMap.put(context, requestList);                }            }            requestList.add(requestHandle);            Iterator<RequestHandle> iterator = requestList.iterator();            while (iterator.hasNext()) {                if (iterator.next().shouldBeGarbageCollected()) { //清理不用的Weak對象                    iterator.remove();                }            }        }        return requestHandle;    }

構造請求返回對象,可以取消請求
RequestHandle requestHandle = new RequestHandle(request);


ResponseHandlerInterface 回調介面定義了 任務的開始，過程，結束還有錯誤訊息
UI訊息在哪裡發送？ 在抽象類別AsyncHttpResponseHandler建構函式裡面

  //UI線程裡面的Handler執行個體化是在建構函式裡面,預設就是myLooper，預設建構函式是傳null的  public AsyncHttpResponseHandler(Looper looper) {        this.looper = looper == null ? Looper.myLooper() : looper;        // Use asynchronous mode by default.預設非同步        setUseSynchronousMode(false);        // Do not use the pool's thread to fire callbacks by default.        setUsePoolThread(false);    }        @Override    public void setUseSynchronousMode(boolean sync) {        // A looper must be prepared before setting asynchronous mode.        if (!sync && looper == null) {            sync = true;            Log.w(LOG_TAG, "Current thread has not called Looper.prepare(). Forcing synchronous mode.");        }        // If using asynchronous mode.        if (!sync && handler == null) {            // Create a handler on current thread to submit tasks            handler = new ResponderHandler(this, looper);//初始化,看ResponderHandler        } else if (sync && handler != null) {            // TODO: Consider adding a flag to remove all queued messages.            handler = null;        }        useSynchronousMode = sync;    }                 private static class ResponderHandler extends Handler {        private final AsyncHttpResponseHandler mResponder;        ResponderHandler(AsyncHttpResponseHandler mResponder, Looper looper) {            super(looper);            this.mResponder = mResponder;        }        @Override        public void handleMessage(Message msg) {            mResponder.handleMessage(msg); //最終提交訊息處理的地方        }    }

AsyncHttpResponseHandler 的子類有多個，包括Binary,Text,JSON 回調

UML 簡單的類圖