android-async-http框架库源码走读
开源项目链接
android-async-http仓库：git clone https://github.com/loopj/android-async-http
android-async-http主页：http://loopj.com/android-async-http/
开始走读分析
依据前一篇的基础使用教程可以发现，首先得到的是AsyncHttpClient实例，所以从这里入手分析一下：
/** * Creates a new AsyncHttpClient with default constructor arguments values */ public AsyncHttpClient() { this(false, 80, 443); } AsyncHttpClient类的这个默认构造函数最终调运了如下AsyncHttpClient(boolean fixNoHttpResponseException, int httpPort, int httpsPort)构造函数，对于默认值设置了HTTP协议的默认端口为80，HTTPS协议的默认端口为443。同时发现可以通过其他构造函数来实例化AsyncHttpClient对象。
/** * Creates new AsyncHttpClient using given params * * @param fixNoHttpResponseException Whether to fix issue or not, by omitting SSL verification * @param httpPort HTTP port to be used, must be greater than 0 * @param httpsPort HTTPS port to be used, must be greater than 0 */ public AsyncHttpClient(boolean fixNoHttpResponseException, int httpPort, int httpsPort) { this(getDefaultSchemeRegistry(fixNoHttpResponseException, httpPort, httpsPort)); } 在该函数中调用了AsyncHttpClient(SchemeRegistry schemeRegistry)构造函数，而真正的实例化获取逻辑过程就在AsyncHttpClient(SchemeRegistry schemeRegistry)方法中，如下所示：
/** * Creates a new AsyncHttpClient. * * @param schemeRegistry SchemeRegistry to be used */ public AsyncHttpClient(SchemeRegistry schemeRegistry) { BasicHttpParams httpParams = new BasicHttpParams(); ConnManagerParams.setTimeout(httpParams, connectTimeout); ConnManagerParams.setMaxConnectionsPerRoute(httpParams, new ConnPerRouteBean(maxConnections)); ConnManagerParams.setMaxTotalConnections(httpParams, DEFAULT_MAX_CONNECTIONS); HttpConnectionParams.setSoTimeout(httpParams, responseTimeout); HttpConnectionParams.setConnectionTimeout(httpParams, connectTimeout); HttpConnectionParams.setTcpNoDelay(httpParams, true); HttpConnectionParams.setSocketBufferSize(httpParams, DEFAULT_SOCKET_BUFFER_SIZE); HttpProtocolParams.setVersion(httpParams, HttpVersion.HTTP_1_1); ClientConnectionManager cm = createConnectionManager(schemeRegistry, httpParams); Utils.asserts(cm != null, "Custom implementation of #createConnectionManager(SchemeRegistry, BasicHttpParams) returned null"); threadPool = getDefaultThreadPool(); requestMap = Collections.synchronizedMap(new WeakHashMap<Context, List<RequestHandle>>()); clientHeaderMap = new HashMap<String, String>(); httpContext = new SyncBasicHttpContext(new BasicHttpContext()); httpClient = new DefaultHttpClient(cm, httpParams); httpClient.addRequestInterceptor(new HttpRequestInterceptor() { @Override public void process(HttpRequest request, HttpContext context) { if (!request.containsHeader(HEADER_ACCEPT_ENCODING)) { request.addHeader(HEADER_ACCEPT_ENCODING, ENCODING_GZIP); } for (String header : clientHeaderMap.keySet()) { if (request.containsHeader(header)) { Header overwritten = request.getFirstHeader(header); Log.d(LOG_TAG, String.format("Headers were overwritten! (%s | %s) overwrites (%s | %s)", header, clientHeaderMap.get(header), overwritten.getName(), overwritten.getValue()) ); //remove the overwritten header request.removeHeader(overwritten); } request.addHeader(header, clientHeaderMap.get(header)); } } }); httpClient.addResponseInterceptor(new HttpResponseInterceptor() { @Override public void process(HttpResponse response, HttpContext context) { final HttpEntity entity = response.getEntity(); if (entity == null) { return; } final Header encoding = entity.getContentEncoding(); if (encoding != null) { for (HeaderElement element : encoding.getElements()) { if (element.getName().equalsIgnoreCase(ENCODING_GZIP)) { response.setEntity(new InflatingEntity(entity)); break; } } } } }); httpClient.addRequestInterceptor(new HttpRequestInterceptor() { @Override public void process(final HttpRequest request, final HttpContext context) throws HttpException, IOException { AuthState authState = (AuthState) context.getAttribute(ClientContext.TARGET_AUTH_STATE); CredentialsProvider credsProvider = (CredentialsProvider) context.getAttribute( ClientContext.CREDS_PROVIDER); HttpHost targetHost = (HttpHost) context.getAttribute(ExecutionContext.HTTP_TARGET_HOST); if (authState.getAuthScheme() == null) { AuthScope authScope = new AuthScope(targetHost.getHostName(), targetHost.getPort()); Credentials creds = credsProvider.getCredentials(authScope); if (creds != null) { authState.setAuthScheme(new BasicScheme()); authState.setCredentials(creds); } } } }, 0); httpClient.setHttpRequestRetryHandler(new RetryHandler(DEFAULT_MAX_RETRIES, DEFAULT_RETRY_SLEEP_TIME_MILLIS)); } 首先通过ConnManagerParams和HttpConnectionParams及HttpProtocolParams设置一些基本参数，譬如版本，timeout时间，max connect count等。接着通过createConnectionManager(schemeRegistry, httpParams);方法创建了一个ClientConnectionManager，其实现类ThreadSafeClientConnManager是一个复杂的实现来管理客户端连接池，它也可以从多个执行线程中服务连接请求。对每个基本的路由，连接都是池管理的。接着通过threadPool = getDefaultThreadPool();初始化网络请求的线程池。接着初始化requestMap，用来与Android Context对应的请求map。初始化clientHeaderMap，用来与放置客户端的请求header map。接着也是一对初始化，完事通过httpClient.setHttpRequestRetryHandler(new RetryHandler(DEFAULT_MAX_RETRIES, DEFAULT_RETRY_SLEEP_TIME_MILLIS));设置重试Handler，会在合适的情况下自动重试。
接下来我们调运的就是AsyncHttpClient里面的各种get、post、delete等方法，通过看代码可以发现它们最终调用的都是sendRequest方法，如下：
/** * Puts a new request in queue as a new thread in pool to be executed * * @param client HttpClient to be used for request, can differ in single requests * @param contentType MIME body type, for POST and PUT requests, may be null * @param context Context of Android application, to hold the reference of request * @param httpContext HttpContext in which the request will be executed * @param responseHandler ResponseHandler or its subclass to put the response into * @param uriRequest instance of HttpUriRequest, which means it must be of HttpDelete, * HttpPost, HttpGet, HttpPut, etc. * @return RequestHandle of future request process */ protected RequestHandle sendRequest(DefaultHttpClient client, HttpContext httpContext, HttpUriRequest uriRequest, String contentType, ResponseHandlerInterface responseHandler, Context context) { if (uriRequest == null) { throw new IllegalArgumentException("HttpUriRequest must not be null"); } if (responseHandler == null) { throw new IllegalArgumentException("ResponseHandler must not be null"); } if (responseHandler.getUseSynchronousMode() && !responseHandler.getUsePoolThread()) { throw new IllegalArgumentException("Synchronous ResponseHandler used in AsyncHttpClient. You should create your response handler in a looper thread or use SyncHttpClient instead."); } 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()); AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest, contentType, responseHandler, context); threadPool.submit(request); RequestHandle requestHandle = new RequestHandle(request); 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()) { iterator.remove(); } } } return requestHandle; } 这个方法的主要作用是将一个新的请求添加到队列线程池中执行。
AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest,contentType, responseHandler, context);这行开始是主要的逻辑，其创建了请求，接着通过threadPool.submit(request);把请求提交到线程池，接着通过RequestHandle requestHandle = new RequestHandle(request);把请求包装到RequestHandle用于之后的取消、管理等操作。
现在来看，发送请求的过程其实重点是创建请求，然后submit到线程池，剩下的事情就交给线程池自己处理了，我们只需要坐等被调用。
现在来看下newAsyncHttpRequest这个逻辑实现：
/** * Instantiate a new asynchronous HTTP request for the passed parameters. * * @param client HttpClient to be used for request, can differ in single requests * @param contentType MIME body type, for POST and PUT requests, may be null * @param context Context of Android application, to hold the reference of request * @param httpContext HttpContext in which the request will be executed * @param responseHandler ResponseHandler or its subclass to put the response into * @param uriRequest instance of HttpUriRequest, which means it must be of HttpDelete, * HttpPost, HttpGet, HttpPut, etc. * @return AsyncHttpRequest ready to be dispatched */ protected AsyncHttpRequest newAsyncHttpRequest(DefaultHttpClient client, HttpContexthttpContext, HttpUriRequest uriRequest, String contentType,ResponseHandlerInterface responseHandler, Context context) { return new AsyncHttpRequest(client, httpContext, uriRequest, responseHandler); } 实质就是得到了一个AsyncHttpRequest的实例，继续看下会发现AsyncHttpRequest implements Runnable，这就是submit到线程池的Runnable了。
至此发送请求过程就结束了。
接收过程更容易，所以不做分析。
总结几句
回过头会发现在我们的请求中最好都加上Context参数，因为这样可以在Activity pause或stop时取消掉没用的请求。
再来整理下整个类功能：
AsyncHttpClient 核心类，使用HttpClient执行网络请求，提供了get，put，post，delete，head等请求方法，使用起来很简单，只需以url及RequestParams调用相应的方法即可，还可以选择性地传入Context，用于取消Content相关的请求，同时必须提供ResponseHandlerInterface（AsyncHttpResponseHandler继承自ResponseHandlerInterface）的实现类，一般为AsyncHttpResponseHandler的子类，AsyncHttpClient内部有一个线程池，当使用AsyncHttpClient执行网络请求时，最终都会调用sendRequest方法，在这个方法内部将请求参数封装成AsyncHttpRequest（继承自Runnable）交由内部的线程池执行。
SyncHttpClient 继承自AsyncHttpClient，同步执行网络请求，AsyncHttpClient把请求封装成AsyncHttpRequest后提交至线程池，SyncHttpClient把请求封装成AsyncHttpRequest后直接调用它的run方法。
AsyncHttpRequest 继承自Runnabler，被submit至线程池执行网络请求并发送start，success等消息。
AsyncHttpResponseHandler 接收请求结果，一般重写onSuccess及onFailure接收请求成功或失败的消息，还有onStart，onFinish等消息。
TextHttpResponseHandler、JsonHttpResponseHandler、BaseJsonHttpResponseHandler这些类都继承自AsyncHttpResponseHandler，只是重写了AsyncHttpResponseHandler的onSuccess和onFailure方法，将请求结果进行了转换而已。
RequestParams 请求参数，可以添加普通的字符串参数，并可添加File，InputStream上传文件。
最近不在状态，深入分析待日后补充。。。