源碼地址：https://github.com/square/okhtt
實例：
okHttpClient = new OkHttpClient.Builder()
.connectTimeout(5*1000, TimeUnit.MILLISECONDS) //鏈接超時
.readTimeout(10*1000,TimeUnit.MILLISECONDS) //讀取超時
.writeTimeout(10*1000,TimeUnit.MILLISECONDS) //寫入超時
.addInterceptor(new HttpHeadInterceptor()) //應用攔截器：統一添加消息頭
.addNetworkInterceptor(new NetworkspaceInterceptor())//網絡攔截器
.addInterceptor(loggingInterceptor)//應用攔截器：打印日誌
.cache(cache) //設置緩存
.build(); Request req = new Request.Builder().url(url).build();
Call call=okHttpClient.newCall(req);//同步調用 Response response = call.execute(); //異步調用 call.enqueue(new CallBack(){ ....});OkHttp構造方法：
OkHttpClient(Builder builder) {
this.dispatcher = builder.dispatcher;
this.proxy = builder.proxy;
this.protocols = builder.protocols;
this.connectionSpecs = builder.connectionSpecs;
//不可變集合
this.interceptors = Util.immutableList(builder.interceptors);
this.networkInterceptors = Util.immutableList(builder.networkInterceptors);
this.eventListenerFactory = builder.eventListenerFactory;
this.proxySelector = builder.proxySelector;
this.cookieJar = builder.cookieJar;
this.cache = builder.cache;
this.internalCache = builder.internalCache;
this.socketFactory = builder.socketFactory;
boolean isTLS = false;
for (ConnectionSpec spec : connectionSpecs) {
isTLS = isTLS || spec.isTls();
}
if (builder.sslSocketFactory != null || !isTLS) {
this.sslSocketFactory = builder.sslSocketFactory;
this.certificateChainCleaner = builder.certificateChainCleaner;
} else {
X509TrustManager trustManager = systemDefaultTrustManager();
this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
}
if (sslSocketFactory != null) {
Platform.get().configureSslSocketFactory(sslSocketFactory);
}
this.hostnameVerifier = builder.hostnameVerifier;
this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(
certificateChainCleaner);
this.proxyAuthenticator = builder.proxyAuthenticator;
this.authenticator = builder.authenticator;
this.connectionPool = builder.connectionPool;
this.dns = builder.dns;
this.followSslRedirects = builder.followSslRedirects;
this.followRedirects = builder.followRedirects;
this.retryOnConnectionFailure = builder.retryOnConnectionFailure;
this.connectTimeout = builder.connectTimeout;
this.readTimeout = builder.readTimeout;
this.writeTimeout = builder.writeTimeout;
this.pingInterval = builder.pingInterval;
if (interceptors.contains(null)) {
throw new IllegalStateException("Null interceptor: " + interceptors);
}
if (networkInterceptors.contains(null)) {
throw new IllegalStateException("Null network interceptor: " + networkInterceptors);
}
} @Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}RealCall.newRealCallOkhttp newCall方法：
@Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}RealCall.newRealCall方法：
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
// Safely publish the Call instance to the EventListener.
RealCall call = new RealCall(client, originalRequest, forWebSocket);
//爲RealCall的成員變量eventListener 賦值
call.eventListener = client.eventListenerFactory().create(call);
return call;
}RealCall execute方法：
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
//設置retryAndFollowUpInterceptor 打印日誌
captureCallStackTrace();
//調用eventListener監聽器，call開始調用了
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}Dispatcher equeue方法：
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
//將call添加到線程池，AsyncCall實現NamedRunnable接口
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}AsynCall run方法：
@Override public final void run() {
String oldName = Thread.currentThread().getName();
Thread.currentThread().setName(name);
try {
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}AsynCall execute方法：
@Override protected void execute() {
boolean signalledCallback = false;
try {
//進入Interceptor遞歸調用返回response
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
signalledCallback = true;
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
}
} catch (IOException e) {
if (signalledCallback) {
// Do not signal the callback twice!
Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
} else {
eventListener.callFailed(RealCall.this, e);
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
}RealCall getResponseWithInterceptorChain()方法：
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>();
//添加用戶攔截器
interceptors.addAll(client.interceptors());
//添加系統攔截器
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
//不是websocket請求就添加，網絡攔截器
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
//真實的網絡請求操作，後續詳細講
interceptors.add(new CallServerInterceptor(forWebSocket));
//實例化RealInterceptorChain，調用proceed方法做遞歸調用
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
return chain.proceed(originalRequest);
}
}RealInterceptorChain 怎麼實現遞歸調用的，proceed()方法：
@Override public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection);
} public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
// If we already have a stream, confirm that the incoming request will use it.
if (this.httpCodec != null && !this.connection.supportsUrl(request.url())) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must retain the same host and port");
}
// If we already have a stream, confirm that this is the only call to chain.proceed().
if (this.httpCodec != null && calls > 1) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must call proceed() exactly once");
}
// Call the next interceptor in the chain.
//實例化下一次調用的InterceptorChain,關鍵點index+1指向interceptors列表的下一項
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//調用當前index指向的interceptors中的攔截器的intercept方法，intercept方法中會再次調用next的proceed方法
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
// Confirm that the next interceptor made its required call to chain.proceed().
if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException("network interceptor " + interceptor
+ " must call proceed() exactly once");
}
// Confirm that the intercepted response isn't null.
if (response == null) {
throw new NullPointerException("interceptor " + interceptor + " returned null");
}
if (response.body() == null) {
throw new IllegalStateException(
"interceptor " + interceptor + " returned a response with no body");
}
return response;
}