OKHttp作为现在Android常用的网络三方框架，为AndroidCoders提供了极大的便利，在使用它的同时，我们也要去深入理解它的工作原理及机制。
概述
一些常用的状态码
- 100~199：指示信息，表示请求已接收，继续处理
- 200~299：请求成功，表示请求已被成功接收、理解
- 300~399：重定向，要完成请求必须进行更进一步的操作
- 400~499：客户端错误，请求有语法错误或请求无法实现
- 500~599：服务器端错误，服务器未能实现合法的请求
基本用法
- 创建OkHttpClient对象
//创建一个OkHttpClient对象
OkHttpClient client = new OkHttpClient();
我们根据源码构造器可以看到，它是一个Builder对象，如下：
public OkHttpClient() {
this(new Builder());
}
public Builder() {
dispatcher = new Dispatcher();
protocols = DEFAULT_PROTOCOLS;
connectionSpecs = DEFAULT_CONNECTION_SPECS;
eventListenerFactory = EventListener.factory(EventListener.NONE);
proxySelector = ProxySelector.getDefault();
cookieJar = CookieJar.NO_COOKIES;
socketFactory = SocketFactory.getDefault();
hostnameVerifier = OkHostnameVerifier.INSTANCE;
certificatePinner = CertificatePinner.DEFAULT;
proxyAuthenticator = Authenticator.NONE;
authenticator = Authenticator.NONE;
connectionPool = new ConnectionPool();
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
- 发起Http请求
//创建Request对象
Request request = new Request.Builder()
.url(url)
.build();
Response response = client.newCall(request).execute();
这里调用response.body().string()方法，获取从服务器上请求下来的结果。
同步网络请求
源码：
@Override public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
try {
client.dispatcher().executed(this);
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
} catch (IOException e) {
eventListener.callFailed(this, e);
throw e;
} finally {
client.dispatcher().finished(this);
}
}
具体用法：
try {
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url("http://www.baidu.com/")
.build();
Response response = client.newCall(request).execute();
String result = response.body().string();
} catch (IOException e) {
e.printStackTrace();
}
这里的execute方法，是Call接口里面的方法，源码就是RealCall实现类里面的execute()方法的具体实现。
/**
* Invokes the request immediately, and blocks until the response can be processed or is in
* error.
*
* <p>To avoid leaking resources callers should close the {@link Response} which in turn will
* close the underlying {@link ResponseBody}.
*
* <pre>@{code
*
* // ensure the response (and underlying response body) is closed
* try (Response response = client.newCall(request).execute()) {
* ...
* }
*
* }</pre>
*
* <p>The caller may read the response body with the response's {@link Response#body} method. To
* avoid leaking resources callers must {@linkplain ResponseBody close the response body} or the
* Response.
*
* <p>Note that transport-layer success (receiving a HTTP response code, headers and body) does
* not necessarily indicate application-layer success: {@code response} may still indicate an
* unhappy HTTP response code like 404 or 500.
*
* @throws IOException if the request could not be executed due to cancellation, a connectivity
* problem or timeout. Because networks can fail during an exchange, it is possible that the
* remote server accepted the request before the failure.
* @throws IllegalStateException when the call has already been executed.
*/
Response execute() throws IOException;
异步网络请求
源码：
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
然后我们去看dispatcher分发器里面的enqueue方法具体实现。
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
具体用法：
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url("http://www.baidu.com/")
.build();
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
e.printStackTrace();
}
@Override
public void onResponse(Call call, Response response) throws IOException {
if (!response.isSuccessful()) {
throw new IOException("Unexpected code " + response);
}
String str = response.body().string();
//TODO 这里得到的str就是返回的数据，而且这里还是子线程，要更新UI请在主线程里面更新
} catch (JSONException e) {
e.printStackTrace();
}
}
});
这里的enqueue方法，是Call接口里面的方法，源码就是RealCall实现类里面的enqueue()方法的具体实现。
/**
* Schedules the request to be executed at some point in the future.
*
* <p>The {@link OkHttpClient#dispatcher dispatcher} defines when the request will run: usually
* immediately unless there are several other requests currently being executed.
*
* <p>This client will later call back {@code responseCallback} with either an HTTP response or a
* failure exception.
*
* @throws IllegalStateException when the call has already been executed.
*/
void enqueue(Callback responseCallback);