this.connectionSpecs = builder.connectionSpecs;

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 = Util.platformTrustManager();

this.sslSocketFactory = newSslSocketFactory(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);

}

}

在new OkHttpClient()内部使用构造器模式初始化了一些配置信息：支持协议、任务分发器（其内部包含一个线程池，执行异步请求）、连接池(其内部包含一个线程池，维护connection)、连接/读/写超时时长等信息。

public Builder() {

dispatcher = new Dispatcher();// 分发器

protocols = DEFAULT_PROTOCOLS;// HTTP 协议

connectionSpecs = DEFAULT_CONNECTION_SPECS;// 传输层版本和连接协议

eventListenerFactory = EventListener.factory(EventListener.NONE);// 事件监听工厂

proxySelector = ProxySelector.getDefault();// 代理选择器

cookieJar = CookieJar.NO_COOKIES;// cookie

socketFactory = SocketFactory.getDefault();// socket 工厂

hostnameVerifier = OkHostnameVerifier.INSTANCE;// 主机名字确认

certificatePinner = CertificatePinner.DEFAULT;// 证书链

proxyAuthenticator = Authenticator.NONE;// 代理服务器身份验证

authenticator = Authenticator.NONE;// 源服务器身份验证

connectionPool = new ConnectionPool();// 连接池

dns = Dns.SYSTEM;// 域名

followSslRedirects = true;// 是否遵循 ssl 重定向

followRedirects = true;// 是否遵循重定向

retryOnConnectionFailure = true;// 连接失败的时候是否重试

connectTimeout = 10_000;// 连接超时

readTimeout = 10_000;// 读超时

writeTimeout = 10_000;// 写超时

pingInterval = 0;// HTTP / 2 和 Web 套接字 ping 之间的时间间隔

}

2.2 Request 对象

Request request = new Request.Builder()

.url(url)

.build();

/Request/

//…

final HttpUrl url;

final String method;

final Headers headers;

final @Nullable RequestBody body;

final Map<Class<?>, Object> tags;

//…

每一次网络请求都是一个Request，Request是对url,method,header,body的封装，也是对Http协议中请求行,请求头,实体内容的封装

通常我们通过构建折模式来构建一个Request对象来来设置一些请求链接（url）、请求方法（method）、请求头（headers）、请求体（body）、标签（tag，可作为取消请求的标记）

2.3 Call对象

Call call = client.newCall(request);

@Override public Call newCall(Request request) {

return RealCall.newRealCall(this, request, false /* for web socket */);

}

static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {

// Safely publish the Call instance to the EventListener.

RealCall call = new RealCall(client, originalRequest, forWebSocket);

call.eventListener = client.eventListenerFactory().create(call);

return call;

}

RealCall 是 Call 的实现类，Call 定义了请求相关的操作，例如同步异步、取消请求等方法。所以后续的请求相关操作基本都是在调用 Call 定义的方法，而这些方法真正的执行是它的实现类 RealCall

2.4请求数据

请求的整个预览图

同步请求 代码如下：

@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);// (1)

Response result = getResponseWithInterceptorChain();// (2)

if (result == null) throw new IOException(“Canceled”);

return result;

} catch (IOException e) {

eventListener.callFailed(this, e);

throw e;

} finally {

client.dispatcher().finished(this);// (3)

}

}

/Dispatcher/

synchronized void executed(RealCall call) {

runningSyncCalls.add(call);

}

// RealCall.java

Response getResponseWithInterceptorChain() throws IOException {

// Build a full stack of interceptors.

// 创建一个拦截器链

List interceptors = new ArrayList<>();

// 应用拦截器

interceptors.addAll(client.interceptors());

interceptors.add(retryAndFollowUpInterceptor);

interceptors.add(new BridgeInterceptor(client.cookieJar()));

interceptors.add(new CacheInterceptor(client.internalCache()));

interceptors.add(new ConnectInterceptor(client));

if (!forWebSocket) {

// 网络拦截器

interceptors.addAll(client.networkInterceptors());

}

interceptors.add(new CallServerInterceptor(forWebSocket));

// originalRequest:我们写的 request

Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,

originalRequest, this, eventListener, client.connectTimeoutMillis(),

client.readTimeoutMillis(), client.writeTimeoutMillis());

return chain.proceed(originalRequest);

}

①根据上面源码我们可以知道getResponseWithInterceptorChain()返回了 Response ，由此可见访问网络从服务器获取数据的操作都在getResponseWithInterceptorChain()内

②这里引入了拦截器链，Request 需要通过拦截器链接收相应的处理最后才会发送到服务器并获取服务器返回的响应

拦截器执行顺序

• 应用拦截器:开发者添加的拦截器

• retryAndFollowUpInterceptor:负责失败重连操作，以及重定向，如果 call 被取消会抛出 IOException

• BridgeInterceptor:作为网络层与应用层之间的桥梁，把(应用层请求)user request转化为(网络层请求)network request，然后向服务器发送network request，得到(网络层响应)network reseponse后转化为(应用层响应) user response

• CacheInterceptor:处理缓存中的 requests 以及把 responses 写到缓存

• ConnectInterceptor:负责与目标服务器建立连接

• 网络拦截器:开发者添加的拦截器

• CallServerInterceptor:拦截器链的最后一个拦截器，负责向服务器发送请求和从服务器获取响应数据

异步请求代码如下

// RealCall.java

@Override public void enqueue(Callback responseCallback) {

synchronized (this) { // 如果这个 call 已经被执行过，抛异常

if (executed) throw new IllegalStateException(“Already Executed”);

executed = true;

}

captureCallStackTrace();

eventListener.callStart(this);

client.dispatcher().enqueue(new AsyncCall(responseCallback));

}

AsyncCall call = new AsyncCall(responseCallback);

Dispatcher dispatcher = client.dispatcher();

dispatcher.enqueue(call);

把 responseCallback 封装成 AsyncCall

返回了一个 Dispatcher

调用任务调度器 Dispatcher 的 enqueue() 异步执行 call

解一下 Dispatcher

// Dispatcher.java

public final class Dispatcher {

// 同步请求和异步请求之和最大值

private int maxRequests = 64;

// 同一个 host 请求数最大值

private int maxRequestsPerHost = 5;

private @Nullable Runnable idleCallback;

/** Executes calls. Created lazily. */

/** 用于执行请求的线程池，且是懒加载的 */

private @Nullable ExecutorService executorService;

/** Ready async calls in the order they’ll be run. */

/** 等待被执行的异步请求 */

private final Deque readyAsyncCalls = new ArrayDeque<>();

/** Running asynchronous calls. Includes canceled calls that haven’t finished yet. */

/** 正在执行的异步请求，包括已经被取消但未完成的请求 */

private final Deque runningAsyncCalls = new ArrayDeque<>();

/** Running synchronous calls. Includes canceled calls that haven’t finished yet. */

/** 正在执行的同步请求，包括已经被取消但未完成的请求 */

private final Deque runningSyncCalls = new ArrayDeque<>();

…

public synchronized ExecutorService executorService() {

if (executorService == null) {

// 核心线程数为0，最大线程数为 Integer.MAX_VALUE ，空闲线程最多存活60秒

executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,

new SynchronousQueue(), Util.threadFactory(“OkHttp Dispatcher”, false));

}

return executorService;

}

synchronized void enqueue(AsyncCall call) {

if (runningAsyncCalls.size() < maxRequests

&& runningCallsForHost(call) < maxRequestsPerHost) {

// 如果正在执行的异步请求数没有达到最大值

// 就放到 runningAsyncCalls 标记为正在执行

runningAsyncCalls.add(call);

// 用 executorService 执行这个异步请求

executorService().execute(call);

} else {

// 如果正在执行的异步请求数达到最大值

// 就放到 readyAsyncCalls 标记为等待执行

readyAsyncCalls.add(call);

}

}

…

}

Dispatcher 是任务调度器，内部建立了一个线程池 ExecutorService ，而且维护了三个集合:

• readyAsyncCalls : 等待被执行的异步请求集合

• runningAsyncCalls : 正在执行的异步请求集合，包括已经被取消但未完成的请求

• runningSyncCalls : 正在执行的同步请求集合，包括已经被取消但未完成的请求

所有异步请求都交由线程池 ExecutorService 来执行。

线程池其实是 ThreadPoolExecutor ，且核心线程数为 0 、最大线程数为Integer.MAX_VALUE、空闲线程存活最大时间为60秒，即所有线程执行完之后空闲60秒就会被销毁，而且存在线程过多导致内存溢出问题等问题，但是在 Dispatcher 的调度下是不会发生线程过多情况的，因为 Dispatcher 限制了正在执行的请求数(同步和异步之和)最大为64，同一个host下请求同时存在数最大值为 5 。

线程池会调用线程执行 AsyncCall 的 execute()

// RealCall.java

final class AsyncCall extends NamedRunnable {

…

@Override protected void execute() {

boolean signalledCallback = false;

try {

// 通过拦截器链得到从服务器获取的响应 Response

Response response = getResponseWithInterceptorChain();

// 如果 retryAndFollowUpInterceptor.cancel() 被调用过就报异常

if (retryAndFollowUpInterceptor.isCanceled()) {

signalledCallback = true; // 标记 callback 回调函数已被调用

responseCallback.onFailure(RealCall.this, new IOException(“Canceled”));

} else {

// 到这里表示获取响应成功

signalledCallback = true; // 标记 callback 回调函数已被调用

responseCallback.onResponse(RealCall.this, response);

}

} catch (IOException e) {

推荐学习资料

• 脑图
  
  
  
  由于文章篇幅问题点击链接查看详细文章以及获取学习笔记：GitHub

responseCallback.onFailure(RealCall.this, new IOException(“Canceled”));

} else {

// 到这里表示获取响应成功

signalledCallback = true; // 标记 callback 回调函数已被调用

responseCallback.onResponse(RealCall.this, response);

}

} catch (IOException e) {

推荐学习资料

• 脑图
  [外链图片转存中…(img-Y9T5PwtW-1646137357977)]
  [外链图片转存中…(img-wLqliOO8-1646137357978)]
  [外链图片转存中…(img-wY5v2Whg-1646137357978)]
  由于文章篇幅问题点击链接查看详细文章以及获取学习笔记：GitHub