/** Opens a connection to the target server and proceeds to the next interceptor. */// 打开一个和目标服务器的连接，并把处理交个下一个拦截器public final class ConnectInterceptor implements Interceptor {public final OkHttpClient client;public ConnectInterceptor(OkHttpClient client) {this.client = client;}@Override public Response intercept(Chain chain) throws IOException {RealInterceptorChain realChain = (RealInterceptorChain) chain;Request request = realChain.request();StreamAllocation streamAllocation = realChain.streamAllocation();// We need the network to satisfy this request. Possibly for validating a conditional GET.boolean doExtensiveHealthChecks = !request.method().equals("GET");// 打开连接HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);RealConnection connection = streamAllocation.connection();// 交个下一个拦截器return realChain.proceed(request, streamAllocation, httpCodec, connection);}
}
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    @Override public Response intercept(Chain chain) throws IOException {Request request = chain.request();streamAllocation = new StreamAllocation(client.connectionPool(), createAddress(request.url()), callStackTrace);...省略代码}
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   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;// 创建连接池connectionPool = new ConnectionPool();dns = Dns.SYSTEM;followSslRedirects = true;followRedirects = true;retryOnConnectionFailure = true;connectTimeout = 10_000;readTimeout = 10_000;writeTimeout = 10_000;pingInterval = 0;
}
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     public final class ConnectionPool {/*** Background threads are used to cleanup expired connections. There will be at most a single* thread running per connection pool. The thread pool executor permits the pool itself to be* garbage collected.*/// 后台定期清理连接的线程池private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true));/** The maximum number of idle connections for each address. */private final int maxIdleConnections;private final long keepAliveDurationNs;// 后台定期清理连接的任务private final Runnable cleanupRunnable = new Runnable() {@Override public void run() {while (true) {// cleanup 执行清理long waitNanos = cleanup(System.nanoTime());if (waitNanos == -1) return;if (waitNanos > 0) {long waitMillis = waitNanos / 1000000L;waitNanos -= (waitMillis * 1000000L);synchronized (ConnectionPool.this) {try {ConnectionPool.this.wait(waitMillis, (int) waitNanos);} catch (InterruptedException ignored) {}}}}}};
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 // 存储连接的双向队列
private final Deque<RealConnection> connections = new ArrayDeque<>();
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void put(RealConnection connection) {assert (Thread.holdsLock(this));if (!cleanupRunning) {cleanupRunning = true;executor.execute(cleanupRunnable);}connections.add(connection);}
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RealConnection get(Address address, StreamAllocation streamAllocation, Route route) {assert (Thread.holdsLock(this));for (RealConnection connection : connections) {if (connection.isEligible(address, route)) {streamAllocation.acquire(connection);return connection;}}return null;
}
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private RealConnection findHealthyConnection(int connectTimeout, int readTimeout,int writeTimeout, boolean connectionRetryEnabled, boolean doExtensiveHealthChecks)throws IOException {
while (true) {//  核心逻辑在 findConnection（）中RealConnection candidate = findConnection(connectTimeout, readTimeout, writeTimeout,connectionRetryEnabled);// If this is a brand new connection, we can skip the extensive health checks.synchronized (connectionPool) {if (candidate.successCount == 0) {return candidate;}}// Do a (potentially slow) check to confirm that the pooled connection is still good. If it// isn't, take it out of the pool and start again.if (!candidate.isHealthy(doExtensiveHealthChecks)) {noNewStreams();continue;}return candidate;
}
}
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private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,boolean connectionRetryEnabled) throws IOException {
Route selectedRoute;
synchronized (connectionPool) {// 省略部分代码...// Attempt to get a connection from the pool. Internal.instance 就是 ConnectionPool 的实例Internal.instance.get(connectionPool, address, this, null);if (connection != null) {// 复用此连接return connection;}// 省略部分代码...// 创建新新连接result = new RealConnection(connectionPool, selectedRoute);// 引用计数acquire(result);
}synchronized (connectionPool) {// Pool the connection. 放入连接池Internal.instance.put(connectionPool, result);}// 省略部分代码...return result;
}
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public void acquire(RealConnection connection) {assert (Thread.holdsLock(connectionPool));if (this.connection != null) throw new IllegalStateException();this.connection = connection;//  连接使用allocations列表来记录每一个引用connection.allocations.add(new StreamAllocationReference(this, callStackTrace));
}
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/** Does all the work necessary to build a full HTTP or HTTPS connection on a raw socket. */private void connectSocket(int connectTimeout, int readTimeout) throws IOException {Proxy proxy = route.proxy();Address address = route.address();rawSocket = proxy.type() == Proxy.Type.DIRECT || proxy.type() == Proxy.Type.HTTP? address.socketFactory().createSocket(): new Socket(proxy);rawSocket.setSoTimeout(readTimeout);try {// 打开 socket 连接Platform.get().connectSocket(rawSocket, route.socketAddress(), connectTimeout);} catch (ConnectException e) {ConnectException ce = new ConnectException("Failed to connect to " + route.socketAddress());ce.initCause(e);throw ce;}// 使用 OKil 连上 socket 后续读写使用 Okiosource = Okio.buffer(Okio.source(rawSocket));sink = Okio.buffer(Okio.sink(rawSocket));}复制代码