[视频教程] 【框架解读】android-async-http-master 源码解读

本帖最后由 Android_Robot 于 2016-10-26 15:16 编辑

先介绍一下android-async-http-master。这个是安卓上的一个开源项目，这个网络请求库是基于Apache HttpClient库之上的一个异步网络请求处理库，网络处理均基于Android的非UI线程，通过回调方法处理请求结果。

使用方法：

先将项目内年jar包引用到工程中。然后将项目中com.loopj.android.http放到工程中，然后就可以使用了。一开始的时候不知道。还是弄了一会儿才发现还得copy一个包进来。

工程调试好之后运行工程。这个开源项目自带了一个如何调用接口的一个demo。

效果如图

里面包括了在开发中常用的几种网络请求类型。

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Class<?> targetClass;
switch (position) {
case 0:
default:
targetClass = GetSample.class;
break;
case 1:
targetClass = PostSample.class;
break;
case 2:
targetClass = DeleteSample.class;
break;
case 3:
targetClass = PutSample.class;
break;
case 4:
targetClass = JsonSample.class;
break;
case 5:
targetClass = FileSample.class;
break;
case 6:
targetClass = BinarySample.class;
break;
case 7:
targetClass = ThreadingTimeoutSample.class;
break;
case 8:
targetClass = CancelAllRequestsSample.class;
break;
case 9:
targetClass = CancelRequestHandleSample.class;
break;
case 10:
targetClass = SynchronousClientSample.class;
break;
}
if (targetClass != null)
startActivity(new Intent(this, targetClass));
}

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在主界面中通过实现onListItemClick()方法调用各个示例类。这个编码风格很好。

先看最常用的get例子

执行一下get操作

getsample代码如下

package com.loopj.android.http.sample;
import org.apache.http.Header;
import org.apache.http.HttpEntity;
import android.util.Log;
import com.loopj.android.http.AsyncHttpClient;
import com.loopj.android.http.AsyncHttpResponseHandler;
import com.loopj.android.http.RequestHandle;
import com.loopj.android.http.ResponseHandlerInterface;
public class GetSample extends SampleParentActivity {
private static final String LOG_TAG = "GetSample";
@Override
public RequestHandle executeSample(AsyncHttpClient client, String URL, Header[] headers, HttpEntity entity, ResponseHandlerInterface responseHandler) {
return client.get(this, URL, headers, null, responseHandler);
}
@Override
public int getSampleTitle() {
return R.string.title_get_sample;
}
@Override
public boolean isRequestBodyAllowed() {
return false;
}
@Override
public boolean isRequestHeadersAllowed() {
return true;
}
@Override
public String getDefaultURL() {
return "https://httpbin.org/get";
}
@Override
public ResponseHandlerInterface getResponseHandler() {
return new AsyncHttpResponseHandler() {
@Override
public void onStart() {
clearOutputs();
}
@Override
public void onSuccess(int statusCode, Header[] headers,
byte[] response) {
debugHeaders(LOG_TAG, headers);
debugStatusCode(LOG_TAG, statusCode);
debugResponse(LOG_TAG, new String(response));
}
@Override
public void onFailure(int statusCode, Header[] headers,
byte[] errorResponse, Throwable e) {
debugHeaders(LOG_TAG, headers);
debugStatusCode(LOG_TAG, statusCode);
debugThrowable(LOG_TAG, e);
if (errorResponse != null) {
debugResponse(LOG_TAG, new String(errorResponse));
}
}
};
}
}

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还是比较简短的。他继承了SampleParentActivity。在SampleParentActivity里已经为主界面设置了主要布局和监听。所以这使得getsample代码很简短。以下是SampleParentActivity中的主要代码和调用步骤。

public void onRunButtonPressed() {
addRequestHandle(executeSample(getAsyncHttpClient(),
(urlEditText == null || urlEditText.getText() == null) ? getDefaultURL() : urlEditText.getText().toString(),
getRequestHeaders(),
getRequestEntity(),
getResponseHandler()));
}

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在SampleParentActivity里已经为run这个button添加了监听，点击后执行上面这个方法。其中addRequestHandle()使子类可以通过重载executeSample()方法而实现不同的功能。

@Override
public void addRequestHandle(RequestHandle handle) {
if (null != handle) {
requestHandles.add(handle);
}
}

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然后是getAsyncHttpClient()方法，得到异步的http链接。是这个开源项目中的核心部分了。在SampleParentActivity类里一开头就声明好了这一个属性。

再看getsample里实现的这个executeSample方法

@Override
public RequestHandle executeSample(AsyncHttpClient client, String URL, Header[] headers, HttpEntity entity, ResponseHandlerInterface responseHandler) {
return client.get(this, URL, headers, null, responseHandler);
}

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主要就是调用AsyncHttpClient类内封装的方法完成操作。
下面主要分析一下AsyncHttpClient类。这个类有1159行代码。所以复制上来不太便于分析，这里根据get的调用及执行步骤进行分析。

当getSamlpe执行AsyncHttpClient的get方法时。调用如下代码。

/**
* Perform a HTTP GET request and track the Android Context which initiated the request with
* customized headers
*
* @param context Context to execute request against
* @param url the URL to send the request to.
* @param headers set headers only for this request
* @param params additional GET parameters to send with the request.
* @param responseHandler the response handler instance that should handle the response.
* @return RequestHandle of future request process
*/
public RequestHandle get(Context context, String url, Header[] headers, RequestParams params, ResponseHandlerInterface responseHandler) {
HttpUriRequest request = new HttpGet(getUrlWithQueryString(isUrlEncodingEnabled, url, params));
if (headers != null) request.setHeaders(headers);
return sendRequest(httpClient, httpContext, request, null, responseHandler,
context);
}

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Context：参数是上下文，这里说一下，android系统中的activity中继承于Context的，所以我们经常在Context参数中传入XXXactivity.this：实际上就是传入本activity的超类。

url ：就不用说了，是请求的地址。在这里是"https://httpbin.org/get";

headers

HTTP是“Hypertext Transfer Protocol”的所写，整个万维网都在使用这种协议，几乎你在浏览器里看到的大部分内容都是通过http协议来传输的，比如这篇文章。

HTTP Headers是HTTP请求和相应的核心，它承载了关于客户端浏览器，请求页面，服务器等相关的信息。

示例当你在浏览器地址栏里键入一个url，你的浏览器将会类似如下的http请求：

GET /tutorials/other/top-20-mysql-best-practices/ HTTP/1.1
Host: net.tutsplus.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Cookie: PHPSESSID=r2t5uvjq435r4q7ib3vtdjq120
Pragma: no-cache
Cache-Control: no-cache

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HttpEntity 翻译过来是http实体，我的理解是http请求的主要内容，如我们如果是post操作那么这个实体内应该是需要post的内容，如果是get操作，那这个实就是服务器内返回过来的数据。所以在getSample里传入为null

ResponseHandlerInterface 这个是项目中自定义的一个handler用于编写在请求开始成功失败，三种情况后需要执行的操作。

继续看。在 AsyncHttpClient的get方法中httpget的构造参数执行了getUrlWithQueryString()方法，这个方法将返回一个String 类型的uri.主要是将参数进行整合最后返回一个带请求参数的uri。下面这个方法的代码

/**

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第一个参数是否转化字符编码把空格替换成%20, 有时候在网址中经常发现原来的空格会被变成%20就是这个道理。
然后参数会被以？参数名=值添加在url后面。RequestParams类型本是一个map表，这里执行了一个getParamString方法将map表转化成字符串并去了空格，根据深度优先的思路进行分析。

protected String getParamString() {

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第二个参数是默认编码类型初值为ut8

protected String contentEncoding = HTTP.UTF_8;

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那么再看getParamsList();

protected List<BasicNameValuePair> getParamsList() {
List<BasicNameValuePair> lparams = new LinkedList();
for (ConcurrentHashMap.Entry<String, String> entry : urlParams.entrySet()) {
lparams.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
}
lparams.addAll(getParamsList(null, urlParamsWithObjects));
return lparams;
}

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返回值是一个链表，类型是基本键值对。是http.message的一个类型。当将所有参数以键值对的方式放在链表里之后又执行了一个addall方法。由于这个不常用所以还是看了一个代码

/**
* Adds the objects in the specified Collection to this {@code LinkedList}.
*
* @param collection
* the collection of objects.
* @return {@code true} if this {@code LinkedList} is modified,
* {@code false} otherwise.
*/
@Override
public boolean addAll(Collection<? extends E> collection) {
int adding = collection.size();
if (adding == 0) {
return false;
}
Collection<? extends E> elements = (collection == this) ?
new ArrayList<E>(collection) : collection;
Link<E> previous = voidLink.previous;
for (E e : elements) {
Link<E> newLink = new Link<E>(e, previous, null);
previous.next = newLink;
previous = newLink;
}
previous.next = voidLink;
voidLink.previous = previous;
size += adding;
modCount++;
return true;
}

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看完就明白了，是将一个集合加在了整个链表上。
那么再看getParamsList方法中的getParamsList(String key, Object value)方法

private List<BasicNameValuePair> getParamsList(String key, Object value) {
List<BasicNameValuePair> params = new LinkedList();
if (value instanceof Map) {
Map map = (Map) value;
List list = new ArrayList<Object>(map.keySet());
// Ensure consistent ordering in query string
Collections.sort(list);
for (Object nestedKey : list) {
if (nestedKey instanceof String) {
Object nestedValue = map.get(nestedKey);
if (nestedValue != null) {
params.addAll(getParamsList(key == null ? (String) nestedKey : String.format("%s[%s]", key, nestedKey),
nestedValue));
}
}
}
} else if (value instanceof List) {
List list = (List) value;
for (Object nestedValue : list) {
params.addAll(getParamsList(String.format("%s[]", key), nestedValue));
}
} else if (value instanceof Object[]) {
Object[] array = (Object[]) value;
for (Object nestedValue : array) {
params.addAll(getParamsList(String.format("%s[]", key), nestedValue));
}
} else if (value instanceof Set) {
Set set = (Set) value;
for (Object nestedValue : set) {
params.addAll(getParamsList(key, nestedValue));
}
} else if (value instanceof String) {
params.add(new BasicNameValuePair(key, (String) value));
}
return params;
}

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这里看到其实是根据value参数的类型提供了不同的构造 List<BasicNameValuePair> 返回值的方法
那么在getParamsList(String key, Object value)的参数urlParamsWithObjects 就是传说中httpentity的数据承载了吧。

protected final ConcurrentHashMap<String, String> urlParams = new ConcurrentHashMap();
protected final ConcurrentHashMap<String, StreamWrapper> streamParams = new ConcurrentHashMap();
protected final ConcurrentHashMap<String, FileWrapper> fileParams = new ConcurrentHashMap();
protected final ConcurrentHashMap<String, Object> urlParamsWithObjects = new ConcurrentHashMap();

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我们看到这个RequestParams类内有四种这样的hashmap用于放数据的变量。所以它应该是根据不同的参数类型选择不同的数据载体.
之前的return URLEncodedUtils.format(getParamsList(), contentEncoding);
是对整个字符串进行编码转换工作，转换成了utf8
那么分析完毕。回到AsyncHttpClient类的get方法

public RequestHandle get(Context context, String url, Header[] headers, RequestParams params, ResponseHandlerInterface responseHandler) {
HttpUriRequest request = new HttpGet(getUrlWithQueryString(isUrlEncodingEnabled, url, params));
if (headers != null) request.setHeaders(headers);
return sendRequest(httpClient, httpContext, request, null, responseHandler,
context);
}

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设置了headers之后执行发送请求

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("Content-Type", contentType);
}
responseHandler.setRequestHeaders(uriRequest.getAllHeaders());
responseHandler.setRequestURI(uriRequest.getURI());
AsyncHttpRequest request = new AsyncHttpRequest(client, httpContext, uriRequest, responseHandler);
threadPool.submit(request);
RequestHandle requestHandle = new RequestHandle(request);
if (context != null) {
// Add request to request map
List<RequestHandle> requestList = requestMap.get(context);
if (requestList == null) {
requestList = new LinkedList();
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();
}
}
}
return requestHandle;
}

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又是好长一段前面包括的是各种错误处理、
在这个方法中看到了

public class AsyncHttpRequest implements Runnable

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这个类实现了runnable接口，这就是为什么这个开源项目可以执行异步请求并且可以控制取消了

@Override
public void run() {
if (isCancelled()) {
return;
}
if (responseHandler != null) {
responseHandler.sendStartMessage();
}
if (isCancelled()) {
return;
}
try {
makeRequestWithRetries();
} catch (IOException e) {
if (!isCancelled() && responseHandler != null) {
responseHandler.sendFailureMessage(0, null, null, e);
} else {
Log.e("AsyncHttpRequest", "makeRequestWithRetries returned error, but handler is null", e);
}
}
if (isCancelled()) {
return;
}
if (responseHandler != null) {
responseHandler.sendFinishMessage();
}
isFinished = true;
}

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在run方法内我们看到。如果responseHandler不为null那么就向它发送开始消息，我们之前看到过这个项目可以对开始成功失败三个状态执行不同的自定义操作就是通过它来实现的。之后开始发送请求

在请求开始之前和开始之后各有一个取消的检查，这就是说如果在请求之前取消请求将不会被执行，为了减少操作。在请求之后取消将不会发送finish消息，避免执行我们自定义的finish方法

在用AsyncHttpRequest声明好runnable对象之后提交到线程池里

threadPool.submit(request);

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这个线程池应该在AsyncHttpClient的构造函数里进行了初值的设置

/**
* Creates a new AsyncHttpClient with default constructor arguments values
*/
public AsyncHttpClient() {
this(false, 80, 443);
}

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这是他的无参构造函数，也就是我们最常用的那个。、
将调用第二个构造函数

public AsyncHttpClient(boolean fixNoHttpResponseException, int httpPort, int httpsPort) {
this(getDefaultSchemeRegistry(fixNoHttpResponseException, httpPort, httpsPort));
}

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getDefaultSchemeRegistry方法用于获得默认的协议模式。比如“http”或“https”同时包含一些协议属性，比如默认端口，用来为给定协议创建java.net.Socket实例的套接字工厂。SchemeRegistry类用来维持一组Scheme，当去通过请求URI建立连接时，HttpClient可以从中选择：

private static SchemeRegistry getDefaultSchemeRegistry(boolean fixNoHttpResponseException, int httpPort, int httpsPort) {
if (fixNoHttpResponseException) {
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)
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;
}

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第一个布尔型参数设置了是否验证其ssl证书。ssl是一种加密协议，

第二个参数是http协议的端口

第三个参数是https使用的端口

然后又将调用Asynchttpclient的第三个构造参数

public AsyncHttpClient(SchemeRegistry schemeRegistry) {
BasicHttpParams httpParams = new BasicHttpParams();
ConnManagerParams.setTimeout(httpParams, timeout);
ConnManagerParams.setMaxConnectionsPerRoute(httpParams, new ConnPerRouteBean(maxConnections));
ConnManagerParams.setMaxTotalConnections(httpParams, DEFAULT_MAX_CONNECTIONS);
HttpConnectionParams.setSoTimeout(httpParams, timeout);
HttpConnectionParams.setConnectionTimeout(httpParams, timeout);
HttpConnectionParams.setTcpNoDelay(httpParams, true);
HttpConnectionParams.setSocketBufferSize(httpParams, DEFAULT_SOCKET_BUFFER_SIZE);
HttpProtocolParams.setVersion(httpParams, HttpVersion.HTTP_1_1);
HttpProtocolParams.setUserAgent(httpParams, String.format("android-async-http/%s (http://loopj.com/android-async-http)", VERSION));
ThreadSafeClientConnManager cm = new ThreadSafeClientConnManager(httpParams, schemeRegistry);
threadPool = Executors.newCachedThreadPool();
requestMap = new WeakHashMap();
clientHeaderMap = new HashMap();
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())
);
}
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));
}