在Android开发中，发送、处理http请求简直太常见了，以至于我们的代码里到处充斥着各种HttpClient和与之相关又臭又长的代码，
它们存在于你代码的各个角落，每次看见都令人作呕，而你仅仅是为了server能返回一个string或者json给你。每次当我自己写这样
的代码时，我都会想能不能简化下这个流程，可能2、3行代码就能搞定。因为针对最简单的case，我只需要提供request url，成功时的
callback和（或）失败时的callback，仅此而已。针对这一类问题（需求），可以说android-async-http提供了几乎完美的解决方案。
通过使用它可以大大简化你的代码，不仅如此，你的代码看上去也优雅多了。
当我第一眼看到它时就被吸引住了，特别是async关键字，干我们这行的都知道，这是异步执行，也就是说它的网络请求自动在非UI
线程里执行，你不需要任何额外的操作（比如手动new一个Thread之类）。项目的官方网站：
http://loopj.com/android-async-http/，对应的github地址：https://github.com/loopj/android-async-http
我这里简要介绍下：它是专门针对Android在Apache的HttpClient基础上构建的异步的callback-based http client。所有的请求
全在UI线程之外发生，而callback发生在创建它的线程中，应用了Android的Handler发送消息机制。你也可以把AsyncHttpClient应用在
Service中或者后台线程中，库代码会自动识别出它所运行的context。它的feature包括：
1. 发送异步http请求，在匿名callback对象中处理response；
2. http请求发生在UI线程之外；
3. 内部采用线程池来处理并发请求；
4. GET/POST 参数构造，通过RequestParams类。
5. 内置多部分文件上传，不需要第三方库支持；
6. 流式Json上传，不需要额外的库；
7. 能处理环行和相对重定向；
8. 和你的app大小相比来说，库的size很小，所有的一切只有90kb；
9. 自动智能的请求重试机制在各种各样的移动连接环境中；
10. 自动的gzip响应解码；
11. 内置多种形式的响应解析，有原生的字节流，string，json对象，甚至可以将response写到文件中；
12. 永久的cookie保存，内部实现用的是Android的SharedPreferences；
13. 通过BaseJsonHttpResponseHandler和各种json库集成；
14. 支持SAX解析器；
15. 支持各种语言和content编码，不仅仅是UTF-8。
大概翻译了下，这些只是大体的概览，具体的细节还得在使用过程中慢慢感受、学习。
接下来，带领大家看看应用android-async-http来写代码是个啥样子。简单来说你只需要3步，
1. 创建一个AsyncHttpClient；
2. （可选的）通过RequestParams对象设置请求参数；
3. 调用AsyncHttpClient的某个get方法，传递你需要的（成功和失败时）callback接口实现，一般都是匿名内部类
，实现了AsyncHttpResponseHandler，类库自己也提供了好些现成的response handler，你一般不需要自己创建一个。
来看看代码如何写：
AsyncHttpClient client = new AsyncHttpClient();
client.get("http://www.google.com", new AsyncHttpResponseHandler() {
@Override
public void onStart() {
// called before request is started
}
@Override
public void onSuccess(int statusCode, Header[] headers, byte[] response) {
// called when response HTTP status is "200 OK"
}
@Override
public void onFailure(int statusCode, Header[] headers, byte[] errorResponse, Throwable e) {
// called when response HTTP status is "4XX" (eg. 401, 403, 404)
}
@Override
public void onRetry(int retryNo) {
// called when request is retried
}
});
是不是很简洁，有没有被震撼到？反正我自己第一次看到的时候有种相见恨晚的感觉，这简直就是我日思夜想的方式啊！这里你只需要通过
匿名内部类的方式实现AsyncHttpResponseHandler，而且更棒的是你只需要override感兴趣的方法，比如一般都是onSuccess和onFailure。
这个版本的get方法没有为请求传递任何参数，当然你也可以通过RequestParams来传递各种参数，如下：
AsyncHttpClient client = new AsyncHttpClient();
RequestParams params = new RequestParams();
params.put("key", "value");
params.put("more", "data");
client.get("http://www.google.com", params, new
AsyncHttpResponseHandler() {
@Override
public void onSuccess(int statusCode, Header[] headers, byte[] response） {
System.out.println(response);
}
@Override
public void onFailure(int statusCode, Header[] headers, byte[] responseBody, Throwable error） {
Log.d("ERROR", error);
}
}
);
以上的例子是返回的response直接是原生字节流的情况，如果你需要把返回的结果当一个String对待，这时只需要匿名实现一个
TextHttpResponseHandler就行，其继承自AsyncHttpResponse，并将原生的字节流根据指定的encoding转化成了string对象，
代码如下：
AsyncHttpClient client = new AsyncHttpClient();
RequestParams params = new RequestParams();
params.put("key", "value");
params.put("more", "data");
client.get("http://www.google.com", params, new
TextHttpResponseHandler() {
@Override
public void onSuccess(int statusCode, Header[] headers, String response） {
System.out.println(response);
}
@Override
public void onFailure(int statusCode, Header[] headers, String responseBody, Throwable error） {
Log.d("ERROR", error);
}
}
);
同样的方式，你可以发送json请求，代码如下：
String url = "https://ajax.googleapis.com/ajax/services/search/images";
AsyncHttpClient client = new AsyncHttpClient();
RequestParams params = new RequestParams();
params.put("q", "android");
params.put("rsz", "8");
client.get(url, params, new JsonHttpResponseHandler() {
@Override
public void onSuccess(int statusCode, Header[] headers, JSONObject response) {
// Handle resulting parsed JSON response here
}
@Override
public void onSuccess(int statusCode, Header[] headers, JSONArray response) {
// Handle resulting parsed JSON response here
}
});
看到了没，返回的response已经自动转化成JSONObject了，当然也支持JSONArray类型，override你需要的那个版本就行。
有了AsyncHttpClient，要实现这些功能是不是很简单呢？当然这里只是很初级的介绍和使用，剩下的还需要开发者自己参考官方
文档、源码（官方甚至提供了一个Sample使用的集合），在实际项目中实践。最后，强烈建议大家使用，是时候和冗长乏味的代码说
我大概浏览了下其代码，关键部分可以分为这4个模块：
1. AsyncHttpClient自己一个模块；
2. AsyncHttpRequest和RequestHandler一个模块；
3. AsyncHttpResponseHandler及其各种特定子类一个模块；
4. RetryHandler，自动重试机制。
我们可以很清楚的看出门道来，大体是按照client、request、response，这样的方式组织的。接下来我们的代码分析也就按照这个顺序进行。
先来说AsyncHttpClient，来看其关键字段和ctor，代码如下：
public static final String LOG_TAG = "AsyncHttpClient";
public static final String HEADER_CONTENT_TYPE = "Content-Type";
public static final String HEADER_CONTENT_RANGE = "Content-Range";
public static final String HEADER_CONTENT_ENCODING = "Content-Encoding";
public static final String HEADER_CONTENT_DISPOSITION = "Content-Disposition";
public static final String HEADER_ACCEPT_ENCODING = "Accept-Encoding";
public static final String ENCODING_GZIP = "gzip";
public static final int DEFAULT_MAX_CONNECTIONS = 10;
public static final int DEFAULT_SOCKET_TIMEOUT = 10 * 1000;
public static final int DEFAULT_MAX_RETRIES = 5;
public static final int DEFAULT_RETRY_SLEEP_TIME_MILLIS = 1500;
public static final int DEFAULT_SOCKET_BUFFER_SIZE = 8192;
private int maxConnections = DEFAULT_MAX_CONNECTIONS;
private int connectTimeout = DEFAULT_SOCKET_TIMEOUT;
private int responseTimeout = DEFAULT_SOCKET_TIMEOUT; // 各种参数设置
private final DefaultHttpClient httpClient; // 包装的Apache DefaultHttpClient
private final HttpContext httpContext;
private ExecutorService threadPool; // 执行网络请求的线程池
private final Map<Context, List<RequestHandle>> requestMap; // 与Android Context对应的请求map
private final Map<String, String> clientHeaderMap; // 客户端的请求header map
private boolean isUrlEncodingEnabled = true; // 允许url encoding
接下来看看各种ctor，如下：
/**
* Creates a new AsyncHttpClient with default constructor arguments values
*/
public AsyncHttpClient() { // 一般客户端代码中都直接调用这个版本的ctor
this(false, 80, 443);
}
/**
* Creates a new AsyncHttpClient.
*
* @param httpPort non-standard HTTP-only port
*/
public AsyncHttpClient(int httpPort) {
this(false, httpPort, 443);
}
/**
* Creates a new AsyncHttpClient.
*
* @param httpPort non-standard HTTP-only port
* @param httpsPort non-standard HTTPS-only port
*/
public AsyncHttpClient(int httpPort, int httpsPort) {
this(false, httpPort, httpsPort);
}
/**
* Creates new AsyncHttpClient using given params
*
* @param fixNoHttpResponseException Whether to fix or not issue, 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));
}
/**
* Returns default instance of SchemeRegistry
*
* @param fixNoHttpResponseException Whether to fix or not issue, 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
*/
private static SchemeRegistry getDefaultSchemeRegistry(boolean fixNoHttpResponseException, int httpPort, int httpsPort) {
if (fixNoHttpResponseException) { // 如果你请求的url是https的，并且遇到了SSL验证之类的错误，那么你应该将此值设为true试试
Log.d(LOG_TAG, "Beware! Using the fix is insecure, as it doesn't verify SSL certificates.");
}
if (httpPort < 1) {
httpPort = 80;
Log.d(LOG_TAG, "Invalid HTTP port number specified, defaulting to 80");
}
if (httpsPort < 1) {
httpsPort = 443;
Log.d(LOG_TAG, "Invalid HTTPS port number specified, defaulting to 443");
}
// Fix to SSL flaw in API < ICS
// See https://code.google.com/p/android/issues/detail?id=13117
SSLSocketFactory sslSocketFactory;
if (fixNoHttpResponseException) { // 感兴趣的同学可自行看看MySSLSocketFactory的实现，基本上是省略了SSL验证环节
sslSocketFactory = MySSLSocketFactory.getFixedSocketFactory();
} else {
sslSocketFactory = SSLSocketFactory.getSocketFactory();
}
SchemeRegistry schemeRegistry = new SchemeRegistry();
schemeRegistry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), httpPort));
schemeRegistry.register(new Scheme("https", sslSocketFactory, httpsPort));
return schemeRegistry;
}
/**
* Creates a new AsyncHttpClient.
*
* @param schemeRegistry SchemeRegistry to be used
*/
public AsyncHttpClient(SchemeRegistry schemeRegistry) { // 最终调到的是这个版本。。。
BasicHttpParams httpParams = new BasicHttpParams();
// 接下来是设置各种参数。。。
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);
ThreadSafeClientConnManager cm = new ThreadSafeClientConnManager(httpParams, schemeRegistry);
// 初始化关键字段
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);
// 设置重试Handler，会在合适的情况下自动重试
httpClient.setHttpRequestRetryHandler(new RetryHandler(DEFAULT_MAX_RETRIES, DEFAULT_RETRY_SLEEP_TIME_MILLIS));
}
接下来重要的就是各种HTTP head、get、post、delete方法，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()) {
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) {
uriRequest.setHeader(HEADER_CONTENT_TYPE, contentType);
}
responseHandler.setRequestHeaders(uriRequest.getAllHeaders());
responseHandler.setRequestURI(uriRequest.getURI());
// 下面的这3行是重点，创建请求，提交请求到线程池，将请求包装到RequestHandle用于之后的取消、管理
AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest, contentType, responseHandler, context);
threadPool.submit(request); // 能submit说明request至少是个Runnable
RequestHandle requestHandle = new RequestHandle(request);
if (context != null) { // 如果Android context非空的话，做一些关联操作，后面可以通过context来取消request的执行
// 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);
}
}
if (responseHandler instanceof RangeFileAsyncHttpResponseHandler)
((RangeFileAsyncHttpResponseHandler) responseHandler).updateRequestHeaders(uriRequest);
requestList.add(requestHandle);
Iterator<RequestHandle> iterator = requestList.iterator();
while (iterator.hasNext()) {
if (iterator.next().shouldBeGarbageCollected()) {
iterator.remove(); // 清理已经完成/取消了的请求
}
}
}
return requestHandle;
}
看到了吧，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。
来看看创建请求的方法，代码如下：
/**
* 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, HttpContext httpContext, HttpUriRequest uriRequest, String contentType, ResponseHandlerInterface responseHandler, Context context) {
return new AsyncHttpRequest(client, httpContext, uriRequest, responseHandler);
}
紧接着我们看看AsyncHttpRequest的实现：
/**
* Internal class, representing the HttpRequest, done in asynchronous manner
*/
public class AsyncHttpRequest implements Runnable { // 这就是submit到线程池的Runnable
private final AbstractHttpClient client;
private final HttpContext context;
private final HttpUriRequest request;
private final ResponseHandlerInterface responseHandler;
private int executionCount;
private boolean isCancelled;
private boolean cancelIsNotified;
private boolean isFinished;
private boolean isRequestPreProcessed;
public AsyncHttpRequest(AbstractHttpClient client, HttpContext context, HttpUriRequest request, ResponseHandlerInterface responseHandler) {
this.client = client;
this.context = context;
this.request = request;
this.responseHandler = responseHandler;
}
/**
* This method is called once by the system when the request is about to be
* processed by the system. The library makes sure that a single request
* is pre-processed only once.
*
* Please note: pre-processing does NOT run on the main thread, and thus
* any UI activities that you must perform should be properly dispatched to
* the app's UI thread.
*
* @param request The request to pre-process
*/
public void onPreProcessRequest(AsyncHttpRequest request) {
// default action is to do nothing...
}
/**
* This method is called once by the system when the request has been fully
* sent, handled and finished. The library makes sure that a single request
* is post-processed only once.
*
* Please note: post-processing does NOT run on the main thread, and thus
* any UI activities that you must perform should be properly dispatched to
* the app's UI thread.
*
* @param request The request to post-process
*/
public void onPostProcessRequest(AsyncHttpRequest request) {
// default action is to do nothing...
}
@Override
public void run() { // 这是在线程池中执行的方法，我们重点看看
if (isCancelled()) { // 检测，如果已经取消了则直接返回，下面的代码有好多次做这个检测，因为你永远不知道什么时候会被取消
return; // 同时也说明了我们的Request是支持取消的
}
// Carry out pre-processing for this request only once.
if (!isRequestPreProcessed) {
isRequestPreProcessed = true;
onPreProcessRequest(this); // callback接口，在一次请求中只调用一次
}
if (isCancelled()) { // 再次检查
return;
}
if (responseHandler != null) {
responseHandler.sendStartMessage(); // 发送开始请求消息
}
if (isCancelled()) { // 检查
return;
}
try {
makeRequestWithRetries(); // 带自动retry机制的请求
} catch (IOException e) {
if (!isCancelled() && responseHandler != null) {
responseHandler.sendFailureMessage(0, null, null, e); // 在没取消的情况下，发送失败消息
} else {
Log.e("AsyncHttpRequest", "makeRequestWithRetries returned error, but handler is null", e);
}
}
if (isCancelled()) { // 检查again
return;
}
if (responseHandler != null) { // 没取消的情况下，发送完成消息
responseHandler.sendFinishMessage();
}
if (isCancelled()) {
return;
}
// Carry out post-processing for this request.
onPostProcessRequest(this); // 处理了请求之后的callback
isFinished = true; // 设置为true表示这个请求执行完毕了
}
private void makeRequest() throws IOException { // 发送一次请求
if (isCancelled()) {
return;
}
// Fixes #115
if (request.getURI().getScheme() == null) {
// subclass of IOException so processed in the caller
throw new MalformedURLException("No valid URI scheme was provided");
}
// 执行请求获得response
HttpResponse response = client.execute(request, context);
if (isCancelled() || responseHandler == null) {
return;
}
// Carry out pre-processing for this response.
responseHandler.onPreProcessResponse(responseHandler, response); // 处理response前
if (isCancelled()) {
return;
}
// The response is ready, handle it.
responseHandler.sendResponseMessage(response); // 发送获得的response
if (isCancelled()) {
return;
}
// Carry out post-processing for this response.
responseHandler.onPostProcessResponse(responseHandler, response); // 处理response后
}
private void makeRequestWithRetries() throws IOException {
boolean retry = true;
IOException cause = null;
HttpRequestRetryHandler retryHandler = client.getHttpRequestRetryHandler();
try {
while (retry) { // 注意这个循环，当retry为false的时候退出
try {
makeRequest();
return; // 请求成功的话，直接返回
} catch (UnknownHostException e) {
// switching between WI-FI and mobile data networks can cause a retry which then results in an UnknownHostException
// while the WI-FI is initialising. The retry logic will be invoked here, if this is NOT the first retry
// (to assist in genuine cases of unknown host) which seems better than outright failure
cause = new IOException("UnknownHostException exception: " + e.getMessage());
retry = (executionCount > 0) && retryHandler.retryRequest(cause, ++executionCount, context);
} catch (NullPointerException e) {
// there's a bug in HttpClient 4.0.x that on some occasions causes
// DefaultRequestExecutor to throw an NPE, see
// http://code.google.com/p/android/issues/detail?id=5255
cause = new IOException("NPE in HttpClient: " + e.getMessage());
retry = retryHandler.retryRequest(cause, ++executionCount, context);
} catch (IOException e) {
if (isCancelled()) {
// Eating exception, as the request was cancelled
return;
}
cause = e;
retry = retryHandler.retryRequest(cause, ++executionCount, context);
}
// 各种异常的情况下，计算retry，看还是否需要retry
if (retry && (responseHandler != null)) { // 需要retry的时候，发送retry消息并附带第几次retry了
responseHandler.sendRetryMessage(executionCount);
}
}
} catch (Exception e) {
// catch anything else to ensure failure message is propagated
Log.e("AsyncHttpRequest", "Unhandled exception origin cause", e);
// 其他的所有不在上述catch里的异常都在这里统一包装成IOException，在最后抛出
cause = new IOException("Unhandled exception: " + e.getMessage());
}
// cleaned up to throw IOException
throw (cause); // 抛出，以便上层代码知道发生了什么
}
public boolean isCancelled() {
if (isCancelled) {
sendCancelNotification();
}
return isCancelled;
}
private synchronized void sendCancelNotification() {
if (!isFinished && isCancelled && !cancelIsNotified) {
cancelIsNotified = true;
if (responseHandler != null)
responseHandler.sendCancelMessage();
}
}
public boolean isDone() {
return isCancelled() || isFinished;
}
public boolean cancel(boolean mayInterruptIfRunning) {
isCancelled = true;
request.abort();
return isCancelled();
}
}
紧接着，我们大概提下RequestHandle，它只是一个持有AsyncHttpRequest对象的弱引用，其方法内部都delegate给了AsyncHttpRequest，
非常简单，感兴趣的同学可自行阅读。
看完了Request，接下来该看看各种Response了，他们都实现了ResponseHandlerInterface接口，这里我们重点看下AsyncHttpResponseHandler，
因为它是后面所有更具体的子类的基础，其ctor代码如下：
/**
* Creates a new AsyncHttpResponseHandler
*/
public AsyncHttpResponseHandler() { // 不指定looper
this(null);
}
/**
* Creates a new AsyncHttpResponseHandler with a user-supplied looper. If
* the passed looper is null, the looper attached to the current thread will
* be used.
*
* @param looper The looper to work with
*/
public AsyncHttpResponseHandler(Looper looper) { // 如果没指定looper的话，会用当前线程的looper顶替
this.looper = looper == null ? Looper.myLooper() : looper;
// Use asynchronous mode by default.
setUseSynchronousMode(false); // 默认是异步的方式，这里异步的意思是指对response的处理发生在与looper
} // 关联的线程中，而不是请求发生的线程池里的线程中
@Override
public void setUseSynchronousMode(boolean sync) {
// A looper must be prepared before setting asynchronous mode.
if (!sync && this.looper == null) {
sync = true; // 一种错误的情况，强制使用同步mode
Log.w(LOG_TAG, "Current thread has not called Looper.prepare(). Forcing synchronous mode.");
}
// If using asynchronous mode.
if (!sync && handler == null) { // 初始化handler
// Create a handler on current thread to submit tasks
handler = new ResponderHandler(this, this.looper);
} else if (sync && handler != null) {
// TODO: Consider adding a flag to remove all queued messages.
handler = null;
}
useSynchronousMode = sync;
}
一般来说，我们会直接在UI线程中调用无参版本的ctor，也就是说response是和UI线程关联的，所有对其的处理handleMessage是发生
在UI线程中的。如果你想用response的结果来更新UI则这是正确的方式。
接着我们看看和处理response相关的代码：
/**
* Avoid leaks by using a non-anonymous handler class.
*/
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) { // 一个简单的Handler，其handleMessage delegate给了mResponder
mResponder.handleMessage(msg);
}
}
// Methods which emulate android's Handler and Message methods
protected void handleMessage(Message message) { // 对各种message的处理，回调各种onXXX方法
Object[] response;
switch (message.what) {
case SUCCESS_MESSAGE:
response = (Object[]) message.obj;
if (response != null && response.length >= 3) {
onSuccess((Integer) response[0], (Header[]) response[1], (byte[]) response[2]);
} else {
Log.e(LOG_TAG, "SUCCESS_MESSAGE didn't got enough params");
}
break;
case FAILURE_MESSAGE:
response = (Object[]) message.obj;
if (response != null && response.length >= 4) {
onFailure((Integer) response[0], (Header[]) response[1], (byte[]) response[2], (Throwable) response[3]);
} else {
Log.e(LOG_TAG, "FAILURE_MESSAGE didn't got enough params");
}
break;
case START_MESSAGE:
onStart();
break;
case FINISH_MESSAGE:
onFinish();
break;
case PROGRESS_MESSAGE:
response = (Object[]) message.obj;
if (response != null && response.length >= 2) {
try {
onProgress((Integer) response[0], (Integer) response[1]);
} catch (Throwable t) {
Log.e(LOG_TAG, "custom onProgress contains an error", t);
}
} else {
Log.e(LOG_TAG, "PROGRESS_MESSAGE didn't got enough params");
}
break;
case RETRY_MESSAGE:
response = (Object[]) message.obj;
if (response != null && response.length == 1) {
onRetry((Integer) response[0]);
} else {
Log.e(LOG_TAG, "RETRY_MESSAGE didn't get enough params");
}
break;
case CANCEL_MESSAGE:
onCancel();
break;
}
}
protected void sendMessage(Message msg) {
if (getUseSynchronousMode() || handler == null) {
handleMessage(msg); // 如果是同步的方式，则handleMessage发生在调用sendMessage的线程中
} else if (!Thread.currentThread().isInterrupted()) { // do not send messages if request has been cancelled
handler.sendMessage(msg); // 否则发生在与handler关联的线程中，一般多为UI线程
}
}
代码中各种sendXXXMessage都会调用这里的sendMessage方法，只是构造的msg的what、obj不同而已。而sendXXXMessage方法
会在request的不同阶段自动被调用，详见AsyncHttpRequest中。下一步我们看眼对response的解析过程，代码如下：
@Override
public void sendResponseMessage(HttpResponse response) throws IOException {
// do not process if request has been cancelled
if (!Thread.currentThread().isInterrupted()) {
StatusLine status = response.getStatusLine();
byte[] responseBody;
responseBody = getResponseData(response.getEntity()); // 将response解析成字节数组
// additional cancellation check as getResponseData() can take non-zero time to process
if (!Thread.currentThread().isInterrupted()) {
if (status.getStatusCode() >= 300) { // 标志失败的情况
sendFailureMessage(status.getStatusCode(), response.getAllHeaders(), responseBody, new HttpResponseException(status.getStatusCode(), status.getReasonPhrase()));
} else { // 成功的情况
sendSuccessMessage(status.getStatusCode(), response.getAllHeaders(), responseBody);
}
}
}
}
/**
* Returns byte array of response HttpEntity contents
*
* @param entity can be null
* @return response entity body or null
* @throws java.io.IOException if reading entity or creating byte array failed
*/
byte[] getResponseData(HttpEntity entity) throws IOException {
byte[] responseBody = null;
if (entity != null) {
InputStream instream = entity.getContent(); // 从entity中读取字节流
if (instream != null) {
long contentLength = entity.getContentLength();
if (contentLength > Integer.MAX_VALUE) {
throw new IllegalArgumentException("HTTP entity too large to be buffered in memory");
}
int buffersize = (contentLength <= 0) ? BUFFER_SIZE : (int) contentLength;
try {
ByteArrayBuffer buffer = new ByteArrayBuffer(buffersize);
try {
byte[] tmp = new byte[BUFFER_SIZE];
int l, count = 0;
// do not send messages if request has been cancelled
while ((l = instream.read(tmp)) != -1 && !Thread.currentThread().isInterrupted()) {
count += l;
buffer.append(tmp, 0, l);
sendProgressMessage(count, (int) (contentLength <= 0 ? 1 : contentLength));
}
} finally {
AsyncHttpClient.silentCloseInputStream(instream);
AsyncHttpClient.endEntityViaReflection(entity);
}
responseBody = buffer.toByteArray();
} catch (OutOfMemoryError e) {
System.gc();
throw new IOException("File too large to fit into available memory");
}
}
}
return responseBody;
}
onXXX方法除了onSuccess和onFailure外都做了默认实现即啥也不做，所以继承至它的子类至少要实现这2个方法，其他的方法你可以选择性实现。
接下来我们看看TextHttpResponseHandler子类的实现，关键代码如下：
@Override // 对上述2个方法的重载，其中将byte[]通过getResponseString方法转化成了String对象
public void onSuccess(int statusCode, Header[] headers, byte[] responseBytes) {
onSuccess(statusCode, headers, getResponseString(responseBytes, getCharset()));
}
@Override
public void onFailure(int statusCode, Header[] headers, byte[] responseBytes, Throwable throwable) {
onFailure(statusCode, headers, getResponseString(responseBytes, getCharset()), throwable);
}
/**
* Attempts to encode response bytes as string of set encoding
*
* @param charset charset to create string with
* @param stringBytes response bytes
* @return String of set encoding or null
*/
public static String getResponseString(byte[] stringBytes, String charset) {
try {
String toReturn = (stringBytes == null) ? null : new String(stringBytes, charset);
if (toReturn != null && toReturn.startsWith(UTF8_BOM)) {
return toReturn.substring(1);
}
return toReturn;
} catch (UnsupportedEncodingException e) {
Log.e(LOG_TAG, "Encoding response into string failed", e);
return null;
}
}
说白了，也就是在父类基础上多了一层处理，将byte[]根据特定的编码转化成String而已，类似的JsonHttpResponseHandler又在此基础上
将String转化成JSONObject或JSONArray，细节不赘述。
ResponseHandler介绍完了，这里我们提下RetryHandler，这个类也很简单，根据内部的白/黑名单等规则来确定是否要retry。
AsyncHttpClient当然也提供了对Cookie的支持，默认是保存在Android的SharedPreferences中，具体代码见PersistentCookieStore。
还有一个功能丰富的RequestParams类，据此你不仅可以为GET/POST方法提供参数，甚至你可以上传本地文件到server端。